Testing & Commissioning Report of

Transcription

1 Testing & Commissioning Report of "66/33KV Olakha Sub-Station" By: Cheten Tshering Olakha Sub-Station, SMD Semtokha. Transmission Department Bhutan Power Corporation Limited Thimphu.

2 BHUTAN POWER CORPORATION LIMITED TRANSMISSION DEPARTMENT SMD, SEMTOKHA 66/33 KV OLAKHA SUB-STATION THIMPHU Commencing of Construction : 13 th June, Testing : October 7-November 27, Test Charge : November 29, Commissioning of Sub Station : December 17, Inauguration :

3 ACKNOWLEDGEMENT I would like to express profound gratitude to the then Officiating General Manager Mr. Nima Dorji for placing me at the up gradation works at 66/33 KV Olakha substation without which, I wouldn t have been able to come out with this report. This provided me an opportunity to learn regarding the testing and commissioning of various switch gears, no sooner I graduated from the college. The placement was very appropriate and at the right time. I wish to extend sincere gratitude to Mr. Chandan Kamti Chatterjee, Testing Engineer, IPPL for teaching me all the practical aspect of the 'Testing and Commissioning' works and also the theoretical part of the same which are beyond the coverage in the books, which he explained through his 22 years of field experience in 'Testing and Commissioning'. I am indebted for his effort in revisiting my report and for making necessary correction and addition. I would also like to offer sincere appreciation which is due to the staff members of SMD Semtokha and Olakha Substation. Amongst the various persons who have helped me in this endeavor, I would like to mention the following: Mr. Sonam Tobgay (Manager), Mr. Tandin Gyeltshen, Mr. Sonam Norbu and Mr. LB Rai. I gratefully acknowledge the extensive literature referred during the course of writing this report. Last but not the least I would like to thank all those who have assisted me directly or indirectly in coming out with this report. Cheten Tshering i

4 ABSTRACT This primary goal of this report is to provide in a simple and more of conventional way of conducting the testing of various switchgears and the system. This report 'Testing and Commissioning Report of 66/33KV Olakha Sub Station' describes about the various testing that are required to be done before commissioning of a substation. It contains in a lucid way, a concise presentation of various technical data and parameters that were obtained while in field testing. This report intends to serve as a history of Olakha substation in terms of its technical data and could be used as future reference while testing however the data may vary with different instruments used and the way it is conducted. This report is also equipped with the practical and pictorial circuit diagram of the exact field testing that was done while in the course of testing. Theories have been provided for every experiment based on the practical hands on experience. The materials presented in this report are intended to serve as a platform from where young and enthusiastic technical people could enhance their learning and explore in the area of testing and commissioning. However it could be used as reference by the one who already have the experience. I would like to solicit the readers' kind suggestions and feedback regarding the report so that I could come up with better one in future. ii

5 List of Figures Figure 1 Experimental set up for checking the winding resistance... 3 Figure 2 Experimental set up for CT Ratio check Figure 3 Experimental setup for ratio test of PT and CVT Figure 4 KPV Testing of Current Transformer Figure 5 Surge Monitor Testing Figure 6 SF6 Circuit Breaker Testing SCOT M3K Timer Figure 7 SF6 Circuit Breaker Testing with Circuit Breaker Operational Analyzer Figure 8 Measurement of Transformer's winding resistance Figure 9 Various testing on Transformer Figure 10 Conditioning of Transformer Oil Figure 11 Winding Resistance Check of 33kv CT & PT Figure 12 Ratio Check of 33kv CT Figure 13 High POT Test (CABLE HV TEST) Figure 14 Inverse-Time, Very-Inverse Time and Extremely-Inverse Time characteristics Figure 15 Testing of IDMT Relays Figure 16 System Stability Testing iii

6 Table of Contents ACKNOWLEDGEMENT... i ABSTRACT... ii List of Figures... iii Checking the Winding Resistance of CT, PT & CVT... 1 CT Ratio Check Ratio Test of CVT and PT Knee Point Voltage Test (KPV Test) of Current Transformer Surge Monitor Testing SF6 Circuit Breaker Testing Transformer Winding Resistance Transformer Testing Transformer Oil Testing Winding Resistance and Ratio Check of 33kv CT & PT High Pot Test (Cable HV Test) Relay Testing (Over Current Protection) Stability Testing Report Reference iv

7 Winding Resistance Check of CT, PT & CVT Checking the Winding Resistance of CT, PT & CVT Bus PT#1 Bus PT#2 CVT#1 CVT#2 CT#1 CT#2 CT#3 CT#4 CT#5 : PT on Tie Line Side : PT on Jemina Line Side : CVT on Tie Line Side : CVT on Jemina Line Side : CT on Tie Line Side : CT on Transformer I Side : CT on Bus Coupler Side : CT on Jemina Line Side : CT on Transformer II Side Aim : 1. To check the Secondary Winding Resistance. 2. Insulation Resistance (IR) checks of primary-earth and secondary-secondary winding by using Megger (2.5KV-5KV). 3. Secondary insulation resistance value check of secondary-earth and secondarysecondary terminals. Objectives : 1. To check the resistance of secondary winding (CT, PT and CVT) and compare with that of name plate rating. 2. To check if there is any short circuit or leakage to ground from primary winding. To check if there is any short circuit between primary and secondary windings. 3. To check if there is any leakage or short circuit between the secondary winding and the earth. To check if there is any short circuit between the secondary windings. Instruments used : Sl. no Description Specification Quantity Remarks 1 Megger 2.5KV-5KV, Mohms, Waco, Type 485/08-09, Sl. no Megger 1KV, 0-200Mohms, Waco, Sl. no Multimeter Digital Multimeter DM3540A, Motwane 1 4 Connecting wires APR NB: Megger uses Ohm's law V=IR. It gives DC voltage and the current which flows through the winding resistance. The reading shown on the Megger is V/I. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 1

8 Winding Resistance Check of CT, PT & CVT Test applied to; PT Core 1, Core 2 and Core 3 of PT R ph Y ph B ph Secondary Winding Terminals A (Primary) N Earth Link Circuit diagram 1a 1n 2a 2n 3a 3n 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 2

9 Winding Resistance Check of CT, PT & CVT Experimental Set up : Multimeter (Ohm meter) Earth Pry-Earth Winding Resistance IR Value check (Meggering) Secondary Winding Resistance Check Earth/Secondary or Secondary-Earth/ Secondary-secondary Figure 1 Experimental set up for checking the winding resistance 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 3

10 Winding Resistance Check of CT, PT & CVT Procedure : 1. Secondary Winding Resistance a. Remove the earth terminal from three phases of PT from the lower side of the box. Make sure there is no connection from the PT to earth. b. Use the Multi meter as ohmmeter and measure the winding resistance of the respective secondary windings and of respective phases. c. Tabulate the reading and compare with the standard/manufacturer value. 2. Insulation resistances check (Meggering). a. Connect the Megger terminal to primary winding and earth terminal. Apply 5KV by Meggering and note down the readings as shown by Megger. NB: Since primary winding is on HV (66KV) side we need to apply high voltage i.e. 5 KV. b. Keeping one of the Megger terminals connected to the primary, connect the other terminal to the various secondary winding one by one. Apply 5KV by Meggering and note down the subsequent readings. 3. Secondary insulation resistances check (Meggering). a. Use lower rating Megger (1KV) for testing. This is because output voltage from the secondary windings is 110V, so we cannot apply very high voltage, otherwise the windings will get burned. b. Connect the Megger to secondary 1- earth terminal, followed by secondary 2- earth and secondary 3-earth terminals respectively. Apply 1 KV by Meggering and note down the subsequent readings. Observations : If there is any short circuit between the windings or earth, then the Megger will show zero value. Else Megger will show some deflections indicating the insulation resistance value. Megger gives DC output 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 4

11 Winding Resistance Check of CT, PT & CVT Results : Bus PT#1, Tie Line PT (Incomer #1) Date:14 /10/09, Wednesday, 3:45pm, Sunny. R-Sl.no. OP 2373/2/7/08, Y-Sl.no. OP 2373/2/3/08, B-Sl.no. OP 2373/2/4/08 Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1a-1n (1&2) a-2n (3&4) a-3n (5&6) IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1(1a) Pry-Sec2(2a) Pry-Sec3(3a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec1 (3a-1a) Bus PT#2, Jemina Line Bus PT (Incomer#2) Date:13 /10/09, Tuesday, 5:30pm, Sunset. R-Sl.no. OP 2373/2/5/08, Y-Sl.no. OP 2373/2/6/08, B-Sl.no. OP 2373/2/8/08 Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1a-1n (1&2) a-2n (3&4) a-3n (5&6) IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1(1a) Pry-Sec2(2a) Pry-Sec3(3a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec1 (3a-1a) KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 5

12 Winding Resistance Check of CT, PT & CVT CVT#1, Tie Line (Incomer #1) Date:9/10/09, Friday. R-Sl.no , Y-Sl.no , B-Sl.no Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1a-1n (1&2) a-2n (3&4) a-3n (5&6) IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1(1a) Pry-Sec2(2a) Pry-Sec3(3a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec1 (3a-1a) CVT#2, Jemina Line (Incomer#2) Date:10 /10/09, Saturday. R-Sl.no , Y-Sl.no , B-Sl.no Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1a-1n (1&2) a-2n (3&4) a-3n (5&6) IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1(1a) Pry-Sec2(2a) Pry-Sec3(3a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec1 (3a-1a) KV/33KV, Olakha Sub Station, Thimphu. Page 6

13 Winding Resistance Check of CT, PT & CVT CT#1, Tie Line (Incomer #1) Date:9/10/09, Friday. R-Sl.no. OC 2373/1/5/08, Y-Sl.no. OC 2373/1/12/08, B-Sl.no. OC 2373/1/10/08 Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-3S S1-4S S1-4S IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1 (1a) Pry-Sec2 (2a) Pry-Sec3 (3a) Pry-Sec4 (4a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec4-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec4 (3a-4a) Sec4-Sec1 (4a-1a) KV/33KV, Olakha Sub Station, Thimphu. Page 7

14 Winding Resistance Check of CT, PT & CVT CT#2, Transformer#1 Side Date:10/10/09, Friday. R-Sl.no. OC 2373/1/15/08, Y-Sl.no. OC 2373/1/9/08, B-Sl.no. OC 2373/1/1/08 Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-3S S1-4S S1-4S IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1 (1a) Pry-Sec2 (2a) Pry-Sec3 (3a) Pry-Sec4 (4a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec4-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec4 (3a-4a) Sec4-Sec1 (4a-1a) KV/33KV, Olakha Sub Station, Thimphu. Page 8

15 Winding Resistance Check of CT, PT & CVT CT#3, Bus Coupler Side Date:10/10/09, Friday. R-Sl.no. OC 2373/1/7/08, Y-Sl.no. OC 2373/1/8/08, B-Sl.no. OC 2373/1/6/08 Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-3S S1-4S S1-4S IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1 (1a) Pry-Sec2 (2a) Pry-Sec3 (3a) Pry-Sec4 (4a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec4-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec4 (3a-4a) Sec4-Sec1 (4a-1a) KV/33KV, Olakha Sub Station, Thimphu. Page 9

16 Winding Resistance Check of CT, PT & CVT CT#4, Jemina Line Side Date:10/10/09, Friday. R-Sl.no. OC 2373/1/14/08, Y-Sl.no. OC 2373/1/2/08, B-Sl.no. OC 2373/1/16/08 Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-3S S1-4S S1-4S IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1 (1a) Pry-Sec2 (2a) Pry-Sec3 (3a) Pry-Sec4 (4a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec4-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec4 (3a-4a) Sec4-Sec1 (4a-1a) KV/33KV, Olakha Sub Station, Thimphu. Page 10

17 Winding Resistance Check of CT, PT & CVT CT#5, Transformer#2 Side Date:10/10/09, Friday. R-Sl.no. OC 2373/1/3/08, Y-Sl.no. OC 2373/1/18/08, B-Sl.no. OC 2373/1/4/08 Secondary Winding Resistance (DM3540A Multimeter) Terminal R-Phase (Ohm) Y-Phase (Ohm) B-Phase (Ohm) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-3S S1-4S S1-4S IR Value Check (Meggering), 5KV. Megger 2.5KV-5KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Pry-Earth Pry-Sec1 (1a) Pry-Sec2 (2a) Pry-Sec3 (3a) Pry-Sec4 (4a) Secondary IR Value check (Meggering), 1KV. Megger 1KV Terminal R-Phase (M-Ohm) Y-Phase (M-Ohm) B-Phase (M-Ohm) Sec1-Earth Sec2-Earth Sec3-Earth Sec4-Earth Sec1-Sec2 (1a-2a) Sec2-Sec3 (2a-3a) Sec3-Sec4 (3a-4a) Sec4-Sec1 (4a-1a) KV/33KV, Olakha Sub Station, Thimphu. Page 11

18 Winding Resistance Check of CT, PT & CVT Precaution : Safety of the experimenter, the first preference. Never start Meggering if both the terminals is being caught by performer Always discharge by connecting the terminal to earth so that the experimenter is free of shock. Conclusion : From this test it is proved that there isn't any leakage or short circuit connection from primary to earth through the casing. Neither is the secondary windings touching the casing or with each other nor the primary winding is in contact with the secondary windings. The Potential transformer is perfectly right. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 12

19 CT Ratio Check CT#1 : CT on Tie line Side CT#2 : CT on Transformer I Side CT#3 : CT on Bus Coupler Side CT#4 : CT on Jemina Line Side CT#5 : CT on Transformer II Side CT Ratio Check Aim : Ratio Test on various Current Transformers. Objective : To check the ratio of primary to secondary current under loaded condition and compare with the name plate rating. Theory : Current transformers (CTs) of all sizes and types find their way into substations to provide the current replicas for metering, controls, and protective relaying. CT performance is characterized by ratio correction factor (turns ratio error), saturation voltage, phase angle error, and rated burden. Bushing CTs are installed in power equipment. They are toroidal, having a single primary turn (the power conductor), which passes through their center. The current transformation ratio results from the number of turns wound on the core to make up the secondary. More than one ratio is often provided by tapping the secondary winding at multiple turn's ratios. The core cross-sectional area, diameter, and magnetic properties determine the CT's performance. Metering CTs are designed with core cross-sections chosen to minimize exciting current effects and are allowed to saturate at fault currents. Larger cores are provided for protection CTs where high current saturation must be avoided for the CT to faithfully reproduce high currents for fault sensing. The exciting current of the larger core at low load is not considered important for protection. Core#1 : Metering. Core#2 : Protection (Over Current, Earth fault, Differential). Core#3 : Bus bar Protection. Core#4 : Bus Bar Protection Zone 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 13

20 CT Ratio Check Instruments used: Sl. no Description Specification Quantity Remarks 1 Auto Transformer 0-260V, 50Hz 1 2 Loading Transformer 230V,50Hz-7.5KVA, 1V/T 1 3 Multimeter AC/DC, Analog, Multi-range 1 4 Clamp leaker DC-10A, Motwane 1 5 Clamp meter Kyoritsu, DCM, Model Connecting wires APR 7 1-Ф Supply 230V, 50Hz 1 Circuit diagram: Clamp meter 1-Ф Supply Auto Transformer Current Transformer Loading Transformer Junction Box Figure 2 Experimental set up for CT Ratio check Clamp Leaker NB: Never open the secondary terminal of CT when primary is connected. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 14

21 CT Ratio Check Procedure : 1. Set up the experiment as shown in the circuit diagram. 2. Make the connections in the junction box so as to get the CT ratio 300/1A. Connect the first terminal and the middle one so that we get the ratio 300/1A i.e. 1S1-1S2, 2S1-2S2, etc. Never leave any CT secondary open. 3. Load the primary with certain percentage of full load current. Increase the load current in steps of 25%, 50%, 75% and 100% of the rated primary current. Observe it on the clamp meter held on the primary side. 4. With the help of clamp leaker measure the current on the secondary side, on each core and note down the readings. 5. Put off the power supply and then make the connections in junction box so as to get 600/1A CT ratio. Connect first terminal and the last terminal i.e. 1S1-1S3, 2S1-2S3, etc. 6. Load the primary with 12.5%, 25%, 37.5% and 50% of the rated primary current and check the values on the clamp meter. 7. With the help of clamp leaker, measure the current in each core i.e. secondary side. For simplicity note down the readings for half core first and then go for full tap readings. 8. Repeat step 1-7 for other two phases also. Precaution : i. Safety the first priority. ii. Never open the secondary terminal of the Current Transformer while it is on loaded condition. iii. Make the connections tight. iv. To avoid over heating of the primary connections, give 100% primary input for the lowest tap and 50% primary input for the full tap. Results : The results are being tabulated for each current transformer. The actual ratio given on the name plate is /1A. The ratio replicates the name plate rating when the applied load current approaches the name plate rating. The errors are more when 12.5% and 25% of the total load current is applied. However as we apply more and more towards the actual load value, the ratio is almost near the actual ratio. The accuracy of CT is expressed in terms of its ratio from its true ratio. This is called ratio error and is expressed as; % 100 Is=Secondary current, Ip=Primary current 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 15

22 CT Ratio Check 1. CT#1, Tie Line Side (Incomer #1) % of Rated Primary Current (A) CT# 1, 1S1-1S2, 300/1A Date: 22/10/09, Thursday, 4:40pm, Sunny. R-Sl.no. OC 2373/1/5/08, Y-Sl.no. OC 2373/1/12/08, B-Sl.no. OC 2373/1/10/08 Applied Primary Current (A) Secondary Current (A) R-phase Y-phase B-phase (A) Ratio % error (A) Ratio % error (A) Ratio % error 25% % % % 50% % % % 75% % % % 100% % % % CT# 1, 1S1-1S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 1, 2S1-2S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 1, 2S1-2S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 1, 3S1-3S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 1, 3S1-3S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 1, 4S1-4S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 1, 4S1-4S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 16

23 CT Ratio Check 2. CT#2, Transformer#1 Side (Incomer #1) % of Rated Primary Current (A) CT# 2, 1S1-1S2, 300/1A Date: 22/10/09, Thursday, 4:55pm, Sunset. R-Sl.no. OC 2373/1/15/08, Y-Sl.no. OC 2373/1/9/08, B-Sl.no. OC 2373/1/1/08 Applied Primary Current (A) Secondary Current (A) R-phase Y-phase B-phase (A) Ratio % error (A) Ratio % error (A) Ratio % error 25% % % % 50% % % % 75% % % % 100% % % % CT# 2, 1S1-1S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 2, 2S1-2S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 2, 2S1-2S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 2, 3S1-3S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 2, 3S1-3S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 2, 4S1-4S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 2, 4S1-4S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 17

24 CT Ratio Check 3. CT#3, Bus Coupler Side % of Rated Primary Current (A) CT# 3, 1S1-1S2, 300/1A Date: 23/10/09, Friday, 9:50am, Sunny. R-Sl.no. OC 2373/1/7/08, Y-Sl.no. OC 2373/1/8/08, B-Sl.no. OC 2373/1/6/08 Applied Primary Current (A) Secondary Current (A) R-phase Y-phase B-phase (A) Ratio % error (A) Ratio % error (A) Ratio % error 25% % % % 50% % % % 75% % % % 100% % % % CT# 3, 1S1-1S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 3, 2S1-2S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 3, 2S1-2S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 3, 3S1-3S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 3, 3S1-3S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 3, 4S1-4S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 3, 4S1-4S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 18

25 CT Ratio Check 4. CT#4, Jemina Line Side (Incomer#2) % of Rated Primary Current (A) CT# 4, 1S1-1S2, 300/1A Date: 22/10/09, Thursday, 6:00pm, Dark. R-Sl.no. OC 2373/1/14/08, Y-Sl.no. OC 2373/1/2/08, B-Sl.no. OC 2373/1/16/08 Applied Primary Current (A) Secondary Current (A) R-phase Y-phase B-phase (A) Ratio % error (A) Ratio % error (A) Ratio % error 25% % % % 50% % % % 75% % % % 100% % % % CT# 4, 1S1-1S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 4, 2S1-2S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 4, 2S1-2S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 4, 3S1-3S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 4, 3S1-3S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 4, 4S1-4S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 4, 4S1-4S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 19

26 CT Ratio Check 5. CT#5, Transformer#2 Side (Incomer#2) % of Rated Primary Current (A) CT# 5, 1S1-1S2, 300/1A Date: 23/10/09, Friday, 10:20am, Sunny. R-Sl.no. OC 2373/1/3/08, Y-Sl.no. OC 2373/1/18/08, B-Sl.no. OC 2373/1/4/08 Applied Primary Current (A) Secondary Current (A) R-phase Y-phase B-phase (A) Ratio % error (A) Ratio % error (A) Ratio % error 25% % % % 50% % % % 75% % % % 100% % % % CT# 5, 1S1-1S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 5, 2S1-2S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 5, 2S1-2S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 5, 3S1-3S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 5, 3S1-3S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % CT# 5, 4S1-4S2, 300/1A 25% % % % 50% % % % 75% % % % 100% % % % CT# 5, 4S1-4S3, 600/1A 12.5% % % % 25.0% % % % 37.5% % % % 50.0% % % % 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 20

27 CT Ratio Check Conclusion : From this experiment, it is proved that the name plate ratio replicates the field test report. However the name plate ratio matches the field test ratio at 100% of the actual load current for lowest tap. For the full tap 50% of the actual load current was provided. The ratio came close to name plate rating at the 50% of the full load current. From this I conclude had we applied the full load current we will be getting exact replicate of the name plate rating. We couldn't apply full load current on 600/1A tap as the primary wire was getting heated up. More or less the obtained results are correct. The ratio error of a CT depends on its exciting current. When the primary current increases, the CT tries to produce corresponding secondary current, and this needs a greater secondary emf, core flux density and exciting current. A stage comes when any further increase in primary current is almost wholly absorbed in an increased exciting current and thereby the secondary current hardly increases at all. At this stage CT becomes saturated. Thus the ratio error depends on saturation. An accuracy of 2-3% of the CT is desirable for distance and differential relays, where as for many other relays, a higher percentage can be tolerated. When the primary current increases, at a certain value the core commences to saturate and the error increases. The value of current at which the error reaches a specified error limit is known as its 'Accuracy Limit Primary Current' or saturation current. The ratio of accuracy limit primary current and the rated primary current is known as rated accuracy limit factor (ALF) or saturation factor, the standard value of which are 5,10,15,20 & KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 21

28 Ratio Test of CVT & PT Ratio Test of CVT and PT CVT#1 CVT#2 PT#1 PT#2 : Capacitive Voltage Transformer (Tie Line side) : Capacitive Voltage Transformer (Jemina side) : Potential Transformer of Bus (Transformer#1 side) : Potential Transformer of Bus (Transformer#2 side) Aim : To find the ratio of primary voltage to the subsequent secondary voltage and then compare with the given ratio in the name plate rating. Objective : To measure the voltage of three cores of each phase on the secondary winding and check if the ratio is alright upon doubling the applied voltage on primary side. Instrument used Sl. no Description Specification Quantity Remarks 1 Auto Transformer 0-260V, 50Hz 1 2 Transformer 230V-3000V, 50Hz 1 3 Multimeter AC/DC, Analog, Multi-range 1 4 Multimeter DM3540A (Motwane) 1 5 Connecting wires APR 6 1-Ф Supply 230V, 50Hz 1 Theory : Potential transformers are used to reduce the system voltage level low enough to suit the ratings of protective relays. The voltage rating of protective relay is usually 110V. The % error is given by; % 100 Where K= Nominal voltage ratio, Vs= Secondary voltage and Vp=Primary voltage. The accuracy of PTs used for meters and instruments is only important at normal system voltage where as PTs used for protection requires errors to be limited over a wide range of voltages under faulty conditions. This may be about 5-150% of nominal voltage. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 22

29 Ratio Test of CVT & PT Test applied to / experimental set up; Circuit diagram Capacitive Voltage Transformer Secondary Voltage Measurement 1 Ф, 230V, 50Hz Supply AVΩ Meter Variac 0-260V, 50Hz Transformer V, 50Hz Figure 3 Experimental setup for ratio test of PT and CVT 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 23

30 Ratio Test of CVT & PT Procedure: 1. Set up the connection as shown below. 2. Connect one wire from HV side of transformer to the top of CVT. 3. Connect the other to the earth. 4. Adjust the voltage from the auto transformer so that 1KV is available on the secondary side of transformer which is shown on the voltmeter. (In fact we are applying 1KV to the primary winding of CVT). 5. Connect a multimeter (Voltmeter) to the core 1, core 2 and core 3 of each phase of CVT upon the application of 1KV to the primary and note down the reading. 6. Repeat the same for other two phases. 7. Repeat step 4 so that we get 2KV on the secondary side of the transformer and follow step 5 and step 6. Results: CVT#1, Tie Line Side Date:12/10/09, Monday, 11:00am, Sunny. R-Sl.no , Y-Sl.no , B-Sl.no Secondary (V) R-Phase Y-Phase B-Phase Core1 Core2 Core3 Core1 Core2 Core 3 Core1 Core2 Core 3 Primary (V) 1000V Ratio % Error 1.7% 1.17% 1.17% -0.83% 1.7% 1.17% -0.83% 1.0% 1.7% 2000V Ratio % Error 2.0% 1.0% -2.0% 2.0% 6.5% 1.0% 2.0% 6.5% 6.5% CVT#2, Jemina Line Date:13/10/09, Tuesday, 10:30am, Sunny. R-Sl.no , Y-Sl.no , B-Sl.no Secondary (V) R-Phase Y-Phase B-Phase Core1 Core2 Core3 Core1 Core2 Core 3 Core1 Core2 Core 3 Primary (V) 1000V Ratio % Error 1.17% 1.17% 1.17% 1.5% 1.5% 1.5% 3.33% 2.17% 2.17% 2000V Ratio % Error 2.33% 2.33% 2.17% 3.67% 3.67% 3.67% 4.33% 4.33% 4.33% 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 24

31 Ratio Test of CVT & PT Bus PT#1 (Transformer#1 side) Date:19/10/09, Monday, 11:35am, Sunny. R-Sl.no. OP 2373/1/7/08, Y-Sl.no. OP 2373/1/3/08, B-Sl.no. OP 2373/1/4/08 Secondary (V) R-Phase Y-Phase B-Phase Core1 Core2 Core3 Core1 Core2 Core 3 Core1 Core2 Core 3 Primary (V) 1000V Ratio % Error -2.5% -2.33% -2.33% -0.17% -0.17% -3.33% -2.0% -0.83% -0.83% 2000V Ratio % Error 1.3% 1.3% 1.5% 2.5% 2.33% 2.33% 1.0% 1.0% 1.0% Bus PT#2 (Transformer#2 side) Date:19/10/09, Monday, 11:35am, Sunny. R-Sl.no. OP 2373/1/5/08, Y-Sl.no. OP 2373/1/6/08, B-Sl.no. OP 2373/1/8/08 Secondary (V) R-Phase Y-Phase B-Phase Core1 Core2 Core3 Core1 Core2 Core 3 Core1 Core2 Core 3 Primary (V) 1000V Ratio % Error -4.83% -4.83% -4.83% 6.3% 6.3% 6.3% 2.0% 4.17% 4.17% 2000V Ratio % Error 1.0% 0.67% 0.67% -1.0% -1.0% -1.0% -1.3% -1.3% -1.3% Observation: 1. From the result obtained the ratio of primary to secondary voltage is within the range where as the actual ratio are 600. The experimented ratio is slightly greater than the actual value / / 3 There is slight error which may be because of the inaccuracy of voltage applied from the transformer. However the results are fairly correct. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 25

32 Ratio Test of CVT & PT Precaution: Safety of the experimenter, the first preference. Always take the reading after it reaches a stable value. Always avoid parallax error while noting the reading. Always give proper connection to CVT and to earth. Conclusion: From this test it is seen that the ratio of primary to secondary voltage is fairly correct with maximum of 6.5% error. For Lab test an error of ±5% is the accepted while for the field test an error of ±15% is accepted. The error can be eliminated by using more accurate meter, and applying the accurate voltage. Since the analog meter was used for noting the reading on the primary side, may be exact voltage wasn t applied, parallax error might have introduced in the process. However the result doesn t deviate much from the exact value thus the name plate rating is ok. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 26

33 KPV Test of Current Transformer Knee Point Voltage Test (KPV Test) of Current Transformer CT #1 CT#2 CT#3 CT#4 CT#5 Aim : Incoming line CT (Tie Line) : CT on Transformer I side : Bus Coupler CT : Incoming line #2 CT (Jemina Line) : CT on Transformer II Side : Knee Point Voltage Testing of Current Transformers. Objective : This test should confirm that at any case the saturation point shouldn t lie before 100% of KPV. It may occur at 110% or higher, doesn t matter but saturation point shouldn't occur before 100% of the KPV. If saturation point occurs before 100% of KPV then the relays will operate before reaching its set value (100%) which is not desirable. To find the saturation point of CT i.e. at what point of voltage it get saturated. Compare the obtained saturation point with that of the name plate rating. Theory : Knee point voltage is the point on the graph obtained between voltage and current beyond which the current rise is very sharp when voltage in increased slightly. When the applied voltage is increased in steps the current also rises in certain step. When the knee point voltage is reached then the current shoots up beyond its normal increasing step. Therefore in this test we see whether the KPV given on the name plate is correct or not. If the saturation point is reached before the actual KPV then the relays are going to trip before fault occurs. In fact the relays should trip upon reaching KPV or later. Therefore for proper coordination and tripping or relays KPV should be checked accurately. Since minimum KVP at lowest tap is provided for core 3 &4 of CT, so we test KPV for only these cores. V KPV 0 I 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 27

34 KPV Test of Current Transformer Instrument used: Sl. no Description Specification Quantity Remarks 1 Auto Transformer 0-260V, 50Hz 1 2 Transformer 230V-3000V, 50Hz 1 3 Multimeter AC/DC, Analog, Multi-range 1 4 Clamp leaker DC-10A, Motwane 1 5 Connecting wires APR 6 1-Ф Supply 230V, 50Hz 1 Name plate rating Procedure: 1. Set up the connection as shown below. 2. Apply certain percentage of Knee point Voltage to Core #3 and Core #4 and then note down the readings as shown by clamp leaker. 3. Repeat the same step for other two phases. 4. Compare the readings. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 28

35 KPV Test of Current Transformer Test applied to/ experimental set up : Current Transformer #1 Sl.No. 2373/1/5/08 Sl.No. 2373/1/12/08 Sl.No. 2373/1/10/08 Current Transformer #3 Sl.No. 2373/1/7/08 Sl.No. 2373/1/8/08 Sl.No. 2373/1/6/08 Clamp leaker 1 Ф, 230V, 50Hz Supply Junction box AVΩ Meter Variac 0-260V, 50Hz Transformer V, 50Hz Figure 4 KPV Testing of Current Transformer 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 29

36 KPV Test of Current Transformer Technical terms: Name plate rating : Minimum Knee Point Voltage at lowest Tap = 325V There are two tapping in each core of CT. Therefore in this case lowest tap refers to the tapping between one end and the middle point. So at full tapping the Knee Point Voltage will be the double of the KPV of lowest tap. P1 P2 Primary 1S1 1S2 1S3 2S1 2S2 2S3 3S1 3S2 3S3 4S1 4S2 4S3 Lowest Tap (325V) Full Tapping (650V) KPV for Core#3 and Core#4 Knee Point Voltage is available for only core #3 and core #4. This is because these cores are specifically designed for protection class core. For protection class core, saturation of current is very important and need to protect the equipment from over current. Whenever the current reaches its saturation point, relay should trip off. Therefore these cores have Knee point Voltage, before which saturation shouldn t occur. Accuracy rating for Core#1 and Core#2 However this is not the case with core#1 and core#2. These cores are specifically designed for metering purposes, where accuracy is of much importance. If saturation point exists for these cores then when the current increases beyond certain value, the meter will stop reading, in fact the meter should record whatever the amount of current drawn. Therefore these cores are rated at 0.2 class of accuracy. For half the winding of each core, the rated KPV is 325V therefore for full winding the rated KPV is 650V. More the number of turns, greater will be the voltage and lesser will be the current, thereby the ratings 325V, 60mA and 650V, 30mA. If the saturation point is reached, CT will make humming sound and must be avoided. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 30

37 KPV Test of Current Transformer Results : 1. Incoming Tie line CT, CT#1 CT# 1, 3S1-3S2, 325V, 60mA at V k /2 Date: 19/10/09, Monday, 3:30pm, Sunny. R-Sl.no. OC 2373/1/5/08, Y-Sl.no. OC 2373/1/12/08, B-Sl.no. OC 2373/1/10/08 % of KPV Applied Voltage (V) R-phase (ma) Y-phase (ma) B-phase (ma) 25% % % % % CT# 1, 3S1-3S3, 650V, 30mA at V k /2 25% % % % % CT#1, 4S1-4S2, 325V, 60mA at V k /2 25% % % % % For demonstration of saturation current, 400V was being applied to B-phase and the current was observed to be 215mA. See the graph. CT#1, 4S1-4S3, 650V, 30mA at V k /2 25% % % % % KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 31

38 KPV Test of Current Transformer 2. CT Transformer 1 side, CT #2 CT# 2, 3S1-3S2, 325V, 60mA at V k /2 Date: 19/10/09, Monday, 4:20, Sunny. R-Sl.no. OC 2373/1/15/08, Y-Sl.no. OC 2373/1/9/08, B-Sl.no. OC 2373/1/1/08 % of KPV Applied Voltage (V) R-phase (ma) Y-phase (ma) B-phase (ma) 25% % % % % CT# 2, 3S1-3S3, 650V, 30mA at V k /2 25% % % % % CT#2, 4S1-4S2, 325V, 60mA at V k /2 25% % % % % CT#2, 4S1-4S3, 650V, 30mA at V k /2 25% % % % % KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 32

39 KPV Test of Current Transformer 3. CT on Bus Coupler, CT #3 CT# 3, 3S1-3S2, 325V, 60mA at V k /2 Date: 19/10/09, Monday, 4:45pm, Sunset. R-Sl.no. OC 2373/1/7/08, Y-Sl.no. OC 2373/1/8/08, B-Sl.no. OC 2373/1/6/08 % of KPV Applied Voltage (V) R-phase (ma) Y-phase (ma) B-phase (ma) 25% % % % % CT# 3, 3S1-3S3, 650V, 30mA at V k /2 25% % % % % CT#3, 4S1-4S2, 325V, 60mA at V k /2 25% % % % % CT#3, 4S1-4S3, 650V, 30mA at V k /2 25% % % % % KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 33

40 KPV Test of Current Transformer 4. CT on Jemina Line CT #4 CT# 4, 3S1-3S2, 325V, 60mA at V k /2 Date: 22/10/09, Thursday, 10:20am, Sunny. R-Sl.no. OC 2373/1/14/08, Y-Sl.no. OC 2373/1/2/08, B-Sl.no. OC 2373/1/16/08 % of KPV Applied Voltage (V) R-phase (ma) Y-phase (ma) B-phase (ma) 25% % % % % CT# 4, 3S1-3S3, 650V, 30mA at V k /2 25% % % % % CT#4, 4S1-4S2, 325V, 60mA at V k /2 25% % % % % CT#4, 4S1-4S3, 650V, 30mA at V k /2 25% % % % % KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 34

41 KPV Test of Current Transformer 5. CT on Transformer#2 side, CT#5 CT# 5, 3S1-3S2, 325V, 60mA at V k /2 Date: 22/10/09, Thursday, 10:50am, Sunny. R-Sl.no. OC 2373/1/3/08, Y-Sl.no. OC 2373/1/18/08, B-Sl.no. OC 2373/1/4/08 % of KPV Applied Voltage (V) R-phase (ma) Y-phase (ma) B-phase (ma) 25% % % % % CT# 5, 3S1-3S3, 650V, 30mA at V k /2 25% % % % % CT#5, 4S1-4S2, 325V, 60mA at V k /2 25% % % % % CT#5, 4S1-4S3, 650V, 30mA at V k /2 25% % % % % KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 35

42 KPV Test of Current Transformer Graphical Analysis for CT#1, 4S1-4S2, 325V, 60mA, B-phase 450 KPV Curve Characteristic Voltage (V) KPV Curve Current (ma) CT#4, 4S1-4S3, 650V, 30mA at V k /2, R-Phase 800 KPV Curve Characterstics Voltage (V) KPV Curve Current (ma) 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 36

43 KPV Test of Current Transformer Precaution : Safety of experimenter and the teams the first priority. Always take the readings after it has settled to a particular value. Make sure that no heavy equipment like welding machines, are operating from the same source from which testing is being done. Always note the name plate reading and then perform the experiment. Conclusion : From this experiment it is proved that the saturation point of current doesn t occur below 100% of KPV. In fact it occurs beyond 110% of the rate KPV. Therefore this equipment is safe to use. If the saturation point occurs before 100% of KPV then the relays connected to it will operate under normal conditions also. When the saturation point occurs, the current rises to a very high value, crossing the set point of relays which makes it to trip off, thus protecting the equipments. This will allow only permissible amount of current to flow through the equipments. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 37

44 Surge Monitor Testing Date : 13/10/09 Day : Tuesday Time : 5:45pm Weather : Sunset Surge Monitor Testing Aim Objective : To check the deflection in the surge monitor. : To find out whether the surge monitor is working or not. Instrument Used : Sl. no. Description Specification Quantity Remarks 1 Megger 1KV, 0-200Mohms, Waco, Sl. no Connecting Wires APR Test applied to/ Test set up; Model : SM T2B 3R Sl.No Lightening Arrester Surge Monitor Megger Figure 5 Surge Monitor Testing 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 38

45 Surge Monitor Testing Procedure: 1. Connect positive terminal of the Megger to the top portion of the surge monitor as shown above. 2. Connect the other terminal to the earth terminal. 3. Start Meggering Observation: When voltage (1KV) was applied to the surge monitor by Meggering, the pointer inside the surge monitor started deflecting. In some case the pointer didn t deflect indicating that the monitor is not working. Precaution : Safety of the experimenter, the first priority. Never start Meggering if both the terminals is being caught by performer Always discharge by connecting the terminal to earth so that the experimenter is free of shock. Conclusion : From this test we can know whether the surge monitor is working or not. If there is no deflection then it is proved that the surge monitor is not working and need to be replaced. If the indicator inside the surge monitor starts to deflect upon the application of voltage then it is proved that the surge monitor is working. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 39

46 SF6 Circuit Breaker Testing SF6 Circuit Breaker Testing CB#1 CB#2 CB#3 CB#4 CB#5 Aim : Circuit Breaker on Incomer#1 (Tie Line) : Circuit Breaker on Transformer#1 side : Circuit Breaker on Bus Coupler Side : Circuit Breaker on Incomer#2 (Jemina Line) : Circuit Breaker on Transformer#2 side : Testing of SF6 Circuit Breaker. Objective : To find out the Alarm 'Loss of SF6' at 20ºC. To find out the General Lock out SF6 at 20ºC. To find the closing and opening time of SF6 Circuit Breaker. Theory : The Nominal pressure of SF6 gas at 20ºC is 6.0 bars. When the loss of SF6 gas occurs below certain set value it gives an alarm indicating less SF6 gas. So we need to attend to it by refilling. If we fail to attend to the alarm, then when the pressure of SF6 gas falls further, then Lock out of SF6 occurs. At this point the circuit breaker neither opens nor closes i.e. it remains in deadlock position. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 40

47 SF6 Circuit Breaker Testing Instruments used : Sl. no Description Specification Quantity Remarks SCOT M3K Time Model no W.166, T&M Pvt. 1 1 Set Interval Meter Ltd., Pune India. Digital Multimeter DM3540A, 2 Multimeter 1 Motwane Refrigerant Leak Model CPS LS790B, Sl.No , 3 1 Detector USA Made Circuit diagram : To Circuit Breaker Junction Box Red : (3, 4, 5) Yellow : 17 Green : 7 for trip 1 and 12 for trip 2 DC +ive, CB Coil Source C +ive, CB Close Coil terminal Source T +ive, CB Trip Coil terminal Source Master Earthing (Double Earthing) Figure 6 SF6 Circuit Breaker Testing SCOT M3K Timer 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 41

48 SF6 Circuit Breaker Testing SF6 Breaker Testing with the Testing Equipment of BPC ( Circuit Breaker Operational Analyzer Model 2406 HISAC, Sl. no ). Master Earthing (Double Earthing) R Y B To Circuit Breaker Junction Box Power Supply Figure 7 SF6 Circuit Breaker Testing with Circuit Breaker Operational Analyzer NB: The terminals from the kit are to be connected as given in the earlier diagram and the wires refer the same definition. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 42

49 SF6 Circuit Breaker Testing Procedure : PART-I 1. Connect the SF6 gas pipe to the breaker and start filling up the gas. 2. Fill up till the pressure reaches 1.0bar. 3. Check all the pipes and SF6 breaker for any leakage with the help of Refrigerant Leak Detector. If leakage is there, then it makes continuous beeping sound. To find the exact leak area, apply shampoo foam over the area. Wherever the pore is, the bubble becomes big and burst out. 4. Leave the Breaker at 1.0bar for few hours. If leakage is there, the pressure falls down. 5. If there is no leakage then fill up the breaker with SF6 gas at 6.0bars. 6. At certain pressure (5.0 bars approx.) general lock out SF6 will occur. The multimeter connected across alarm (X1-4, K11-A1) and trip contact (X1-4, K10-A1) will make continuity sound. 7. Increase the pressure until it reaches certain point (5.3bars approx.) when the multimeter connected across alarm and trip contact stops making continuity sound. This is the Alarm Loss of gas pressure. 8. Still fill up the breaker with SF6 gas until the pressure reaches 6.0bars and disconnect it. PART-II 1. Set up the experiment with SCOT M3K Time Interval Meter. 2. Connect the RYB terminals at the top and middle (make and break) points and plug it to the SCOT M3K Time Interval Meter. 3. Connect two ground wires so as to have effective earthling. If one fails other will work. 4. Connect the control cable with the Circuit Breaker a. Red one is DC +ive and it is the CB coil source. DC signals flows from Breaker to the SCOT M3K Time Interval Meter. Connect it to X1-3, 4, and 5. b. The command (Close command and Trip command) that we give flows to the CB through the other two wires. c. The yellow wire is C +ive and it is the close coil terminal. The close command that we punch goes through this cable to operate the CB. Connect it to X1-17. d. Green wire is T +ive and is the Trip coil terminal. The trip command that we punch passes through this wire to trip the CB. Connect it to X Supply AC power to the motor so that it energizes the spring. When spring compresses to its set position, the limit switch disconnects the AC supply and the motor stops, thus the spring is charged. 6. Give the close, open-1 and close/open command consecutively with simultaneous recording of the time (ms). 7. Change the green terminal to X1-12 and give open-2 command and note down the readings. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 43

50 SF6 Circuit Breaker Testing Results : Sl. No. Temperature (ºC) 2009/IND/03/ /IND/03/ /IND/03/ /IND/03/ /IND/03/ /10/2009, Sunday, Sunny. 66KV Circuit Breaker SF6 gas filling Pressure Density Monitor Status. Trip Contact X1-4 K10-A1 X1-4 K10-A1 X1-4 K10-A1 X1-4 K10-A1 X1-4 K10-A1 Lockout gas pressure (bar) kg/cm 2 Status found Alarm Contact 5.1 Leakage X1-4 K11-A1 5.2 OK X1-4 K11-A1 5.0 OK X1-4 K11-A1 5.2 OK X1-4 K11-A1 5.0 OK X1-4 K11-A1 Loss of SF6 gas pressure Status found (bar) 5.3 Leakage 5.4 OK 5.3 OK 5.4 OK 5.3 OK Sl. No. Motor Sl. No. Close Coil (Ω) Trip Coil 1(Ω) Trip Coil 2(Ω) 2009/IND/03/ /IND/03/ /IND/03/ /IND/03/ /IND/03/ KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 44

51 SF6 Circuit Breaker Testing Test Result of SF6 Circuit Breaker Location : Bus Coupler Side. Type : 3AP1FG Serial Number : 2009/IND/03/6061. Make : SEIMENS Date of Testing : 26/10/2009, 9:45am, Sunny. STC : 40KA Feeder Name : CB3 Rated Voltage : 145KV Rated Current : 3150A Phase Closing/Opening Time Close (ms) Open-1 (ms) Open-2(ms) C/O(ms) R Y B Coil Resistance Coil Resistance (Ω) Close coil 48.5 Trip Coil Trip Coil Test Result of SF6 Circuit Breaker Location : Transformer#2 Side. Type : 3AP1FG Serial Number : 2009/IND/03/6062. Make : SEIMENS Date of Testing : 26/10/2009, 10:25am, Sunny. STC : 40KA Feeder Name : CB5 Rated Voltage : 145KV Rated Current : 3150A Phase Closing/Opening Time Close (ms) Open-1 (ms) Open-2(ms) C/O(ms) R Y B Coil Resistance Coil Resistance (Ω) Close coil 49.7 Trip Coil Trip Coil KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 45

52 SF6 Circuit Breaker Testing Test Result of SF6 Circuit Breaker Location : Transformer#1 Side. Type : 3AP1FG Serial Number : 2009/IND/03/6058. Make : SEIMENS Date of Testing : 26/10/2009, 11:00am, Sunny. STC : 40KA Feeder Name : CB2 Rated Voltage : 145KV Rated Current : 3150A Phase Closing/Opening Time Close (ms) Open-1 (ms) Open-2(ms) C/O(ms) R Y B Coil Resistance Coil Resistance (Ω) Close coil 50.9 Trip Coil Trip Coil Test Result of SF6 Circuit Breaker Location : Incomer#1 Tie Line Side. Type : 3AP1FG Serial Number : 2009/IND/03/6060. Make : SEIMENS Date of Testing : 26/10/2009, 11:20am, Sunny. STC : 40KA Feeder Name : CB1 Rated Voltage : 145KV Rated Current : 3150A Phase Closing/Opening Time Close (ms) Open-1 (ms) Open-2(ms) C/O(ms) R Y B Coil Resistance Coil Resistance (Ω) Close coil 50.4 Trip Coil Trip Coil KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 46

53 SF6 Circuit Breaker Testing Test Result of SF6 Circuit Breaker Location : Incomer#2 Jemina Line Side. Type : 3AP1FG Serial Number : 2009/IND/03/6059. Make : SEIMENS Date of Testing : 28/12/2009, 4:15pm, Sunny. STC : 40KA Feeder Name : CB4 Rated Voltage : 145KV Rated Current : 3150A Phase Closing/Opening Time Close (ms) Open-1 (ms) Open-2(ms) C/O(ms) R Y B Coil Resistance Coil Resistance (Ω) Close coil 48.9 Trip Coil Trip Coil Result : The rated time for closing is 50±8 ms; therefore the value that we obtained is within the range. The rated opening time is 30±4 ms; therefore the value we obtained is within the permissible limit. The rated close-open time is 30±10 ms; therefore the value we obtained is within the normal range. Precaution : Safety the first priority. Always take the steady value. Connect the wires properly and tightly. Note down the readings properly. Conclusion : From this field test I came to learn that the results are correct and the SF6 circuit breaker is safe to use. Of course one SF6 circuit breaker on Jemina side had leakage therefore it was replaced and tested. Rests of the circuit breaker are working fine. Sometimes the tripping coil gets burned often as in case of Jemina line circuit breaker, the reason being the flow of continuous current, low resistance of the coil and appearance of high voltage across its terminal. For resistance check, apply voltage across the terminals for 15s and then check the current obtained and cross check with the actual value. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 47

54 Transformer Winding Resistance Transformer Winding Resistance Aim : To find out the Winding Resistance of Transformer and of its respective CTs. Objective : To check the winding resistance of Transformer in R, Y and B phase on HV side. To check the winding resistance on LV side at Tap # 9. To check the winding resistance of WTICT, NCT and LV phase CT. Theory : There are three current transformers in 20MVA Transformer viz. winding temperature indicator current transformer (WTICT), Neutral current transformer (NCT) and LV phase current transformers. WTICT is connected to the bellow heater in the WTI. When transformer is loaded the current flows through the CT and flows through the heater coil, thereby the temperature indicated by WTI becomes the winding oil temperature and the winding temperature. In no load condition the WTI temperature and the OTI temperature are same as indicated in the dehydration curve. NCT is located below the neutral point in secondary winding and for each LV phases there is CT. Tap # 9 is normal position with turn's ratio two, so whenever we do normal test we take tap # 9. For this test we simply use Ohm's law. Transformer 1 Sl. no /1 WTICT NCT LV Phase CT : 350/5A, CL-5, 20VA. : Core (i), 400/1A, 5P10, 10VA Core (ii), 400/1A, 5P10, 10VA Core (iii), 400/1A, CL-PS, Vk 800V. Imag 100mA at Vk, RCT 1.5Ω Core (i), 400/1A, 5P10, 10VA. Core (ii), 400/1A, 5P10, 10VA Core (iii), 400/1A, CL-PS, Vk 800V. Imag 100mA at Vk, RCT 1.5Ω Connections: WTICT (15, 16). NCT (18, 19, 20). LV R-Ph CT (21, 22, 23), LV Y-Ph CT (24, 25, 26), LV B-Ph CT (27, 28, 29). 15-2WS7, 16-2WS8 17-2WS9 18-2S1, 2S2 19-2S3, 2S4 20-2S5, 2S6 21-2US1, 2US2 22-2US3, 2US4 23-2US5, 2US6 24-2VS1, 2VS2 25-2VS3, 2VS4 26-2VS5, 2VS6 27-2WS1, 2WS2 28-2WS3, 2WS4 29-2WS5, 2WS6 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 48

55 Transformer Winding Resistance Instruments used : Sl. no Description Specification Quantity Remarks 1 AVΩ Meter Motwane 1 2 Multimeter Digital Multimeter DM3540A, Motwane 1 3 Connecting wires APR Circuit diagram : N.B: Part I and II refers to connections of different experiment. Figure 8 Measurement of Transformer winding resistance 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 49

56 Transformer Winding Resistance Procedure : 1. Disconnect the earth terminal from the neutral point. 2. Position the tap at Connect a wire to the R-phase (incoming) whose end will be connected to +ive supply and connect a wire from the other end and connect it to voltmeter. 4. Connect a wire to the Y-phase (incoming) whose end will be connected to -ive supply and connect a wire from the other end and connect it to voltmeter. 5. Connect an ammeter to the negative wire. 6. Switch on the power supply and note down the readings on voltmeter and ammeter. 7. Calculate the resistance from the values observed. 8. Increase the tap to next level and repeat step 1 to7. 9. Repeat the above step for Y-B and B-R phases. 10. For LV side repeat the above step for R-N, Y-N, B-N and B-Y, however here we need not change the tapings. Just position at the normal tap. 11. To find the winding resistance of CT connect ohmmeter across respective terminals i.e. 15,16,17,18,19,20,21,22,23,24,24,25,26,27,28 and 29 in our case. 12. Record the reading. Result : Transformer 1, Sl. No /1 Date: 3/11/09, 11:00am, Sunny. R-Y Phase Y-B Phase Tap Position Current (A) Voltage (V) Resistance (mω) Tap Position Current (A) Voltage (V) Resistance (mω) b b KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 50

57 Transformer Winding Resistance Transformer 1, Sl. No /1 Date: 3/11/09, 11:00am, Sunny. B-R Phase LV Side Tap # 9 Tap Current Voltage Resistance Position (A) (V) (mω) Phase b Transformer 1, Sl. No /1. Neutral CT (NCT) Current (A) Voltage (V) Resistance (mω) R-N Y-N B-N B-Y In LV side, the Line resistance is double to that of Phase Resistance. WTICT TB No. Wire Code Resistance (Ω) TB No. Wire Code Resistance (Ω) 18 2S1-2S2 15 2WS7 19 2S3-2S4 16 2WS8 20 2S5-2S6 16 2WS8 LV Phase CTs 17 2WS9 TB No. Wire Code Resistance (Ω) 15 2WS7 21 2US1-2US2 17 2WS9 22 2US3-2US4 23 2US5-2US6 24 2VS1-2VS2 25 2VS3-2VS4 26 2VS5-2VS6 27 2WS1-2WS2 28 2WS3-2WS4 29 2WS5-2WS6 For WTICT we have to do with pair of wires alternatively. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 51

58 Transformer Winding Resistance Transformer 2, Sl. No /2 Date: 4/11/09, 12:40pm, Sunny. R-Y Phase Y-B Phase Tap Position Current (A) Voltage (V) Resistance (mω) Tap Position Current (A) Voltage (V) Resistance (mω) b b Transformer 2, Sl. No /2 Date: 4/11/09, 12:00am, Sunny. B-R Phase LV Side Tap # 9 Tap Position Current (A) Voltage (V) Resistance (mω) b Phase Current (A) Voltage (V) Resistance (mω) R-N Y-N B-N B-Y In LV side, the Line resistance is double to that of Phase Resistance. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 52

59 Transformer Winding Resistance Neutral CT (NCT) Transformer 2, Sl. No /2. WTICT TB No. Wire Code Resistance (Ω) TB No. Wire Code Resistance (Ω) 18 2S1-2S WS7 19 2S3-2S WS8 20 2S5-2S WS8 LV Phase CTs 17 2WS9 TB No. Wire Code Resistance (Ω) 15 2WS7 21 2US1-2US WS9 22 2US3-2US US5-2US VS1-2VS VS3-2VS VS5-2VS WS1-2WS WS3-2WS WS5-2WS For WTICT we have to do with pair of wires alternatively. Precautions : Safety of experimenter the first priority. Always adjust the DC voltage level as per the ranges of the meters used. Avoid parallax error. Conclusion : From this field test, the winding resistances of CTs are below 1.5Ω. As indicated on the name plate rating. The winding resistance of NCT, LV Phase CTs and WTICT are permissibly correct. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 53

60 Transformer Testing Transformer Testing (IR Check, Ratio Check, Magnetizing Balance Check, Magnetizing Current Check, Vector Group Check) Aim : 1. To check the 'Insulation Resistance' of the Transformer. 2. To check the 'Ratio of HV-LV winding'. 3. To check the 'Magnetizing Balance' or 'Core Balance'. 4. To check the 'Magnetizing Current'. 5. To check the 'Vector Group'. Objectives : To find out the insulation resistance between HV-Earth, LV-Earth and HV-LV terminals and to ensure there is no leakage to earth i.e. continuity check. To ensure that the turns ratio for each tapping is in accordance to the name plate rating. To ensure that the magnetic balance is not disturbed. To observe the no load magnetizing current. To ensure the vector group DYN 11. Theory : I. Insulation Resistance Test Insulation resistance of a two-winding transformer insulation system, HV to ground, LV to ground, and HV to LV is determined with a Megger type of instrument. Historically, insulation resistance measurements are also made to assess the amount of moisture in transformer insulation. However, the measurement of insulation dissipation factor has shown to be a better indicator of the overall condition of insulation in a power transformer. II. Ratio Test The purpose of this test is to ensure that all windings have the correct number of turns according to the design. Since the transformer is equipped with a load tap changer (LTC), ratio tests is also carried out at the various positions of the tap changer(s). The objective of ratio tests at different tap positions is to ensure that all winding taps are made at the correct turns and that the tap connections are properly made to the tap changing devices. ANSI/IEEE general standard [1] requires that the measured voltage ratio between any two windings be within ± 0.5% of the value indicated on the nameplate. To verify this requirement, ratio tests are performed in which the actual voltage ratio is determined through measurements. Ratio tests can be made by energizing the transformer with a low AC test voltage and measuring the voltage induced in other windings at various tap settings, etc. In each case the voltage ratio is calculated and compared to the voltage ratio 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 54

61 Transformer Testing indicated on the transformer's nameplate. More commonly, Transformer Turns Ratio (TTR) test sets are used for making the tests. III. Magnetizing Balance Test This test is performed to ensure that the HV and LV windings are not displaced from its original 120º displacement from respective phases. In this, two phase supply is applied to one of the winding and the induced voltages on the other two windings are measured. The voltage applied on the windings should be the sum of the voltage induced on other two windings. If the phase displacements are correct then the flux distribution on each winding will also be proportionate i.e. upon repeating the applied voltage to other phases too, the sum of induced voltages should be equal to the applied voltage. In the readings one will see the maximum value being in the diagonal. In case of LV side which is star connected, magnetic balance test ensures that the windings are not displaced with respect to the neutral point. If windings are displaced from each other then we say neutral is displaced, which means some currents are flowing in the neutral point (Earth Fault). By KCL, current flowing in the neutral point should be zero at balanced condition however practically it is not true. Therefore in order to satisfy this condition neutral point is grounded so that any current flowing through neutral point goes to earth. Here too the diagonal characteristic is observed. IV. Magnetizing Current Check This test ensures that the magnetizing current under no load condition doesn t exceed 4% of the rated current. When voltage is applied to the exciting or primary winding of the transformer, a magnetizing current flows in the primary winding which produces the flux in the core. The flow of flux in magnetic circuits is analogous to the flow of current in electrical circuits. The magnetizing current is required to magnetize the winding and the core. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 55

62 Transformer Testing Magnetizing Current V. Vector Group Check This test is from the design point of consideration and is required to check the vector group indicated on the name plate of the transformer. There are various vector groups and in our case the transformer is Dy11. Some of the typical examples are as follows. The vector diagram for Dy11 is shown below. 30 Lag or +30 Here, RYB forma an equilateral triangle. R-b=R-y, Y-b=Y-y, R-Y=R-N+Y-N, B-y is the shoot point. This confirms the Dy11 vector group test. Dy11 66KV/33KV, Olakha Sub Station, Thimphu. Page 56

63 Transformer Testing Instrument required : Sl. no Description Specification Quantity Remarks 1 Motorized Megger 5KV, MΩ, Sl. no , WACO 1 2 Multimeter Digital Multimeter DM3540A, Motwane 1 3 Clamp Leaker DC-10A, Motwane 1 4 Testing Board MCB C16 attached, handmade 1 See picture 5 Connecting wires 2.5 sq.mm APR 6 Transformer Sl. no 21067/1, 20MVA Ф Supply 415V, 50Hz 1 8 AVΩ Meter AC/DC Range 1 9 Screw Driver -type 1 Circuit diagram : Figure 9 Various testing on Transformer 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 57

64 Transformer Testing Procedure : I. Insulation Resistance Check a. Connect wires from HV, LV and Earth terminals. b. Use 5KV Motorized Megger with external power supply. c. Connect HV and Earth terminals to the Megger. Switch on the power supply and note down the readings indicated on the Megger at 15 th and 60 th seconds. d. Switch off the Megger and discharge the current in the lines used by shorting the terminals to avoid risk of shock. e. Connect LV and Earth terminals to the Megger. Switch on the power supply and note down the readings indicated on the Megger at 15 th and 60 th seconds. f. Repeat step d. g. Connect HV and LV terminals to the Megger. Switch on the power supply and note down the readings indicated on the Megger at 15 th and 60 th seconds. h. Repeat step d. i. Calculate R 15 /R 60 and then tabulate the readings. II. Ratio Test a. Connect the circuit diagram as in the figure above. b. Disconnect the neutral from Earth terminal. c. Apply 3-Ф power from nearby BMK to the connection board. d. Since the transformer has 17 taps, begin one by one. e. Positioning the tap at 01, check the voltage at HV side, LV side (line as well as phase voltage) and note down the readings. f. Increase the tap to next level and then repeat step 'e'. g. Repeat step 'f' till the highest tap. h. Tabulate the readings for further analysis. III. Magnetizing Balance Check (Core Balance), Tap # 9b. a. The experiment continues from above tests. b. Make sure that the table for recording data is made sequentially. c. Switch on the power supply and always work offline. d. Remove the HV B-phase out and then measure the voltage on HV lines and LV side (Line as well as phase voltages). e. Remove the HV R-phase out and then measure the voltage on HV lines and LV side (Line as well as phase voltages). f. Remove the HV Y-phase out and then measure the voltage on HV lines and LV side (Line as well as phase voltages). Switch off the power supply. g. Record the data sequentially and correctly. h. Observe the characteristic of the readings on the table. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 58

65 Transformer Testing IV. Magnetizing Current Check (No load current), Tap # 9b. a. Reconnect every connection as shown in the circuit diagram. b. Switch on the power supply but while changing the connections switch it off. c. Disconnect the R-phase on HV side and then measure the current on R-phase itself. Record the voltage on R-Y phase too. Use Clamp leaker. d. Reconnect R-phase and disconnect the Y-phase on HV side. Measure the current on Y-phase itself. Record the voltage on Y-B phase too. Use Clamp leaker. e. Reconnect Y-phase and disconnect the B-phase on HV side. Measure the current on B-phase itself. Record the voltage on Y-B phase too. Use Clamp leaker. f. Disconnect HV side and give the supply to LV terminals. g. Use clamp leaker to measure the current in the lines. h. Disconnect the r-phase on LV side and then measure the current on r-phase itself. Record the voltage on r-y phase too. i. Reconnect r-phase and disconnect the y-phase on LV side. Measure the current on y-phase itself. Record the voltage on y-b phase too. j. Reconnect y-phase and disconnect the b-phase on LV side. Measure the current on b-phase itself. Record the voltage on b-r phase too. k. Observe the readings very carefully such that the magnetizing current is not less than 4% of the actual rated current in both the cases. V. Vector Group Check, Tap # 9b. a. Reconnect every connection as shown in the circuit diagram. b. Here we need to check the name plate rating. The vector Group is Dy11 so we need to prove this. Refer the vector diagram given in theory. c. Short the R-phase of HV and LV terminals. d. Apply voltage on HV side. e. Check the voltage R-Y, Y-B, B-R, R-n, Y-n, R-b, R-y, Y-b, Y-y, B-b and B-y terminals. f. Check if the results are matching with that given in theory. Precautions : 1. Safety of experimenter the first priority. 2. While Meggering, always discharge the current to avoid shock. 3. Always switch off the power supply when connecting the circuit to avoid spark. Insulation Resistance Values of Power Transformers (MΩ) Class Winding Temperatures C KV 20 C 30 C 40 C 50 C 60 C 70 C R R R60-Value of IR at 60sec & R15 at 15 sec. after the application of test voltage of Megger Courtesy: Installation, commissioning and maintenance of electrical equipment, Tarlok Singh 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 59

66 Transformer Testing Result : TRANSFORMER # 1, Sl. no 21067/1 Transformer Testing, Sl. No /1 Date : 30/10/2009, 12:00pm, Sunny. Insulation Resistance (IR) Check by 5KV Motorized Megger (MΩ) Terminals IR-R 60 IR-R 15 R 15 /R 60 HV-Earth HV-LV LV-Earth Transformer Testing, Sl. No /1 Magnetizing Balance Check (Tap #9) or Core Balance Ф-out R-Y(V) Y-B(V) B-R(V) r-y(v) y-b(v) b-r(v) r-n(v) y-n(v) b-n(v) B R Y Transformer Testing, Sl. No /1 Magnetizing Current Check (Tap # 9) or No Load Current HV Side LV Side Applied Applied Ф-out Current (ma) Ф-out Current (ma) Voltage(V) Voltage (V) R R-Y R-ph 3.50 r r-y r-ph 9.63 Y Y-B Y-ph 2.46 y y-b y-ph 6.30 B B-R B-ph 2.49 b b-r b-ph 9.82 Terminals Voltage(V) R-Y Y-B B-R R-N Y-N B-b B-y R-b R-y Y-b Y-y Transformer Testing, Sl. No /1 Vector Group Check (Tap # 9), Dy11 R-b=R-y, Y-b=Y-y, R-Y=R-N+Y-N, B-y is the shoot point. These conditions are found correct. Dy11 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 60

67 Ratio Test of Transformer Tap HV ( ) Side (Volts) Ratio Test of Transformer # 1, Sl. no 21067/1 LV (Star) Side (Volts) Actual Ratio Ratio % Error V RY V YB V BR v ry v yb v br v rn v yn v bn HV/LV Rph Yph Bph Rph Yph Bph % -1.82% -0.45% % -1.38% 0.00% % -0.93% 0.00% % -0.94% -0.94% % -0.48% -0.48% % -0.96% 0.00% % -0.98% 0.00% % -0.99% -0.49% 9b % -1.00% 0.00% % -1.01% 0.00% % -1.03% 0.00% % -1.04% 0.00% % -1.05% -0.53% % -0.53% -0.53% % -1.08% 0.00% % -1.64% 0.00% % -1.11% -0.56% 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 61

68 Transformer Testing TRANSFORMER # 2, SL. No /2 Transformer Testing, Sl. No /2 Date : 4/11/2009, 10:00am, Sunny. Insulation Resistance (IR) Check by 5KV Motorized Megger (MΩ) Terminals IR-R 60 IR-R 15 R 15 /R 60 HV-Earth HV-LV LV-Earth Transformer Testing, Sl. No /2 Magnetizing Balance Check (Tap #9) or Core Balance Ф-out R-Y(V) Y-B(V) B-R(V) r-y(v) y-b(v) b-r(v) r-n(v) y-n(v) b-n(v) B R Y Transformer Testing, Sl. No /2 Magnetizing Current Check (Tap # 9) or No Load Current HV Side LV Side Applied Applied Ф-out Current (ma) Ф-out Current (ma) Voltage(V) Voltage(V) R R-Y R-ph 3.90 r r-y r-ph 11.0 Y Y-B Y-ph 2.00 y y-b y-ph 6.50 B B-R B-ph 2.20 b b-r b-ph 11.0 Terminals Voltage(V) R-Y Y-B B-R R-N Y-N B-y R-b R-y Y-b Y-y Transformer Testing, Sl. No /1 Vector Group Check (Tap # 9), Dy11 R-b=R-y, Y-b=Y-y, R-Y=R-N+Y-N, B-y is the shoot point. These conditions are found correct. Dy11 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 62

69 Ratio Test of Transformer Tap HV ( ) Side (Volts) Ratio Test of Transformer # 2, Sl. no 21067/2 LV (Star) Side (Volts) Actual Ratio Ratio % Error V RY V YB V BR v ry v yb v br v rn v yn v bn HV/LV Rph Yph Bph Rph Yph Bph % +0.24% +0.43% % +0.23% +0.33% % +0.40% +0.35% % +1.04% +0.15% % +0.04% +0.33% % +0.53% +0.64% % +0.51% -0.21% % +0.23% +0.04% 9b % +0.43% +0.29% % +0.01% +0.16% % +0.52% +0.38% % +0.21% -0.12% % +0.68% +0.82% % +0.40% +0.48% % +0.44% +0.03% % +0.04% -0.62% % +0.32% +0.15% 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 63

70 Transformer Testing Result: The field testing of the ratio of HV/LV at various tapings is found correct with slight errors. The phase voltage of secondary is also found to be 1/ 3 times that of line voltage. The actual ratio at normal tap is 2 i.e. 66/33KV. It is observed in the magnetizing balance check that the maximum voltage exists across the diagonal element for HV and LV phase voltage. NB: If the diagonal characteristics holds true for the phase voltages at LV side then it is true for HV side. Further Vector Group check will also hold true. The vector group check for Dy11 also proved the equations or the vector characteristic given. Conclusion: From the above field test it is proved that the results obtained are tallying with the name plate ratings. Ratios at various taps are correct with some errors. The windings at the core are also balanced at 120 from each other. The magnetizing current as observed during the field test is far below 4% of the actual rated current. No load current should not exceed above 4% of the actual rated current. It is observed that in the Y phase the current is comparatively less. The reason being, the Y phase winding lies at the middle so the flux gets distributed equally to other windings too thereby resulting in low currents. Whereas in other case very less flux gets to the third winding (see the fig. below). The vector group is found to be Dy11. There are a total of about 63 vector group, some of which are given at the theory portion. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 64

71 Dehydration, Filtration and Testing of Transformer Oil Transformer Oil Testing Aim : Dehydration & filtration of Transformer oil in the Transformer. Objective : 1. To remove the moisture present in the core, windings, tank, radiator and the conservator tank. 2. To check the insulation resistance (IR Value) of the Transformer using Megger and observe the reading. 3. Check the Breakdown Voltage value (BDV) of the dehydrated oil. Theory : After the erection of Transformer at site, dehydration and filtration of oil is very important. Here 'Transformer Oil Conditioning Machine' is used. There are two outlets in this machine; one is used as incoming oil source and the other acts as outgoing source. After connecting one pipe to the transformer tank and the other to the oil barrel start the machine and fill the transformer with oil. Don t fill it fully; as transformer oil gets heated its volume expands. Now connect both pipes to transformer where one draws oil from the transformer and the other pumps in the dehydrated oil coming from the Transformer oil conditioning machine. There are moistures present in core and windings. When the oil is heated, by virtue of core and windings being immersed in the oil, it gets heated. As a result of this the moisture present, in the core and windings vaporize out and gets mixed with the oil. This oil is then passed into the oil conditioning machine. The oil passes through 'degassing chamber' in two stages where the oil is set to flow in the form of fountain. When this process happens the moisture is sent out from the oil which is then sucked by the vacuum pump. The oil further passes through heater and filter vessel where the oil gets heated and gets filtered of carbon deposits, dirt, sludge, etc. particles. The oil is again pumped in the transformer. It heats the core and the process continues. During the process of Transformer Oil Conditioning, check the IR value of the transformer every after one hour. Theoretically the Megger value should come down and then rise up until it attains a stable value. When it attains stable value for multiple Meggering then it shows that the oil is dehydrated. Then collect sample oil for BDV test. The BDV value shouldn t come below 60KV. While Meggering we go with checking the insulation resistance value of primary-earth, secondary-earth and primary-secondary winding (see fig. 1). The theory behind is as follows; Primary-Earth : Basically we are observing the change in the characteristics of the insulation resistance between primary winding and the earth. The IR value of primary to earth will be high before conditioning. When the conditioning of the oil is started the moisture gets removed and the value comes down. Upon further conditioning the IR value will go up indicating that there is no conduction path from primary to earth. Secondary-Earth : Here we are checking the insulation resistance between secondary winding and the earth terminal. The same characteristic should be observed as described above. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 65

72 Dehydration, Filtration and Testing of Transformer Oil Primary-Secondary : The insulation resistance of primary-secondary is observed. Upon heating, dehydrating and filtering, the IR value should come down and the rise up until it attains a stable value. Thus moisture is indicated, vaporized and removed out. IR Value Pry-Earth IR Value Pry-Sec IR Value Sec-Earth Sample Graph Fig. 1 IR Value 0 Time 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 66

73 Dehydration, Filtration and Testing of Transformer Oil Instruments used: Sl. no Description Specification Quantity Remarks 1 Transformer oil Sl. no , Supply 415V, conditioning machine 165.2KW, 238Amperes. 1 Set 2 Multimeter Digital Multimeter DM3540A, Motwane 1 3 Motorized Megger 5KV, MΩ, Sl. no , WACO 1 4 Connecting wires 2.5 sq.mm APR Circuit diagram Transformer Oil Conditioning Machine HV LV Earth Motorized Megger Internal diagram Figure 10 Conditioning of Transformer Oil 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 67

74 Dehydration, Filtration and Testing of Transformer Oil Procedure : PART I 1. Connect the pipes at respective inlet and outlet of the Transformer oil conditioning machine. 2. Connect the other end to the oil drum and the inlet to the 'Top Oil Filter Valve' of the transformer tank. 3. Start the machine and fill up the transformer to certain level but not fully so that when at peak temperature of the oil the volume expanded will not overflow the oil from the transformer. 4. When heating the oil, please observe the source load and the load that the one heater absorbs. (In our case the source load was 130A whereas each heater consumes 80A. There are three heaters, so we were bound to switch on only one heater.) 5. Now for dehydration and filtration, connect the pipe connecting the oil drum to the 'Bottom Oil Filter Valve' of the transformer tank. 6. Start the machine with one heater being switched on. 7. Disconnect the earth terminal from the neutral point. Start Meggering with HV-Earth, LV-Earth and HV-LV and record the reading every one hour until the readings comes down and rise up to attain a stable value. N.B The process may go on for two to three days. Then put off the heater and cool the oil with machine under running condition. 8. Take the oil sample (two bottles) for Breakdown Voltage test. The average of six readings obtained should be above 60KV. This ends the dehydration and filtration test. PART II (BDV Test) 1. Arrange the BDV testing kit (Automatic Oil Test Set OTS100AF/Megger) 2. Wash the oil container thoroughly with oil form one bottle. 3. Pour the oil sample from other bottle and place it in the testing kit. 4. Adjust the space between the electrodes to 2.5mm. 5. Keep it idle for 15minutes so that the oil sample settles down. 6. Set the standard to IEC and then press the button to apply voltage. Precaution : Safety of the experimenter the first priority. Make sure not to fill the transformer tank fully so that the oil will not overflow when heated at peak temperature. Drying of a transformer must be done under continuous and competent supervision. Careful observation of temperature is essential during drying as high temperature can result in damage to the insulation. No sparks or smoking should be allowed in the vicinity of a transformer being dried. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 68

75 Dehydration, Filtration and Testing of Transformer Oil Results : Date/Time Dehydration and Filtration of Transformer Oil Transformer #1, 20MVA, 66/33KV, Sl. no /1. IR by 5KV Motorized Motor (MΩ) Temperature (ºC) Date Time HV-Earth LV-Earth HV-LV Machine oil OTI WTI Remarks 26/10/ /10/ :56am :25pm :30pm :30pm :18pm :20pm :25pm :30pm :30am :35am :30am :30am :30am :30am :30am :30am :30am :30pm :30pm :30pm :30pm :30pm :30pm :30pm :30pm :30pm :30pm :30pm With the help of thermostat the maximum temperature was fixed at 60 C. 4:20pm, interruption, oil overflow from breather. 5:12pm, Machine started after draining the oil. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 69

76 Dehydration, Filtration and Testing of Transformer Oil Date/Time Dehydration and Filtration of Transformer Oil Transformer #1, 20MVA, 66/33KV, Sl. no /1. IR by 5KV Motorized Motor (MΩ) Temperature (ºC) Date Time HV-Earth LV-Earth HV-LV Machine oil OTI WTI Remarks 28/10/ :30am :30am :30am :30am :30am :30am :30am :30am :30am :30am :30am :30am :30pm :30pm :30pm :30pm :30pm :30pm :30pm, interruption, Supply went off. 2:10pm, Machine started. Radiators Radiator Open (Time) Close (Time) Remarks 1 10:15am 10:50am 2 11:00am 11:40am 3 12:30pm 1:30pm 4 1:30pm 2:40pm 5 2:40pm 3:10pm 6 3:10pm 3:40pm 7 3:40pm 4:10pm 8 4:10pm 4:40pm 9 5:10pm 5:40pm 10 6:10pm 6:30pm All radiators opened on 28/10/2009 at 6:30pm. Heater switched off and cooling of the oil started with machine under running condition. Machine stopped at 29/10/2009 at 9:45am. Oil sample taken for BDV Test at SMD, Semtokha. OLTC Filtration started at 4:00pm till 6:00pm on 29/10/ KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 70

77 Dehydration, Filtration and Testing of Transformer Oil Breakdown Voltage Test of the Sample Oil Taken from Transformer#1. Date: 29/10/2009, 10:55am at Semtokha. Experimenter: Pema Jampel. Equipment : Automatic Oil Test Set (OTS100AF/Megger) Readings Time (Minutes) BDV(KV) 1 st Reading nd Reading rd Reading th Reading th reading th Reading Average = 75.2KV Graphical Analysis : Transformer Oil Characteristic Curve HV-Earth :56am 3:30pm 7:25pm 2:35am 8:30am 11:30am 2:30pm 5:30pm 8:30pm 11:30pm 2:30am 5:30am 8:30am 11:30am 3:30pm 6:30pm IR Value Transformer Oil Characteristic Curve Time 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 71

78 Dehydration, Filtration and Testing of Transformer Oil Transformer Oil Characteristic Curve LV Earth IR Value Transformer Oil Characteristic Curve LV Earth 0 11:56am 3:30pm 7:25pm 2:35am 8:30am 11:30am 2:30pm 5:30pm 8:30pm 11:30pm 2:30am 5:30am 8:30am 11:30am 3:30pm 6:30pm Time Transformer Oil Characteristic curve HV-LV IR Value TransformerOil Characteristic curve HV-LV 0 11:56am 3:30pm 7:25pm 2:35am 8:30am 11:30am 2:30pm 5:30pm 8:30pm 11:30pm 2:30am 5:30am 8:30am 11:30am 3:30pm 6:30pm Time 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 72

79 Dehydration, Filtration and Testing of Transformer Oil Date/Time Dehydration and Filtration of Transformer Oil Transformer #2, 20MVA, 66/33KV, Sl. no /2. IR by 5KV Motorized Motor (MΩ) Temperature (ºC) Date Time HV-Earth LV-Earth HV-LV Machine oil OTI WTI Remarks 30/10/ /10/2009 1/11/2009 1:00pm :00pm :00pm :00pm :00pm :00pm :00pm :00pm :00pm :00pm :00pm :00am :00am :00am :00am :00am :00am :00am :00am :00am :00am :00am :00am :00pm :00pm :00pm :00pm :00pm :00pm, Filtration started with all radiators open. All radiators closed at 3:00pm on 31/10/09. 66KV/33KV, Olakha Sub Station, Thimphu. Page 73

80 Dehydration, Filtration and Testing of Transformer Oil Date/Time Dehydration and Filtration of Transformer Oil Transformer #2, 20MVA, 66/33KV, Sl. no /2. IR by 5KV Motorized Motor (MΩ) Temperature (ºC) Date Time HV-Earth LV-Earth HV-LV Machine oil OTI WTI Remarks 1/11/2009 2/11/2009 3/11/2009 5:00pm :00pm :00pm :00pm :00pm :00pm :00pm :00am :00am :00am :00am :00am :00am :00am :00am :00am :00am :00am :00am :00pm :00pm :00pm :00pm :00pm :00pm :00pm One pair of Radiators opened and closed after every one hour subsequently. Started at 11:00am till 4:30pm. All Radiator s opened at 4:30pm, 2/11/09 for cooling. Machine stopped at 4:00pm, 3/11/09 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 74

81 Dehydration, Filtration and Testing of Transformer Oil Breakdown Voltage Test of the Sample Oil Taken from Transformer#2. Date: 3/11/2009, 10:45am at Semtokha. Experimenter: Pema Jampel. Equipment : Automatic Oil Test Set (OTS100AF/Megger) Readings Time (Minutes) BDV(KV) 1 st Reading nd Reading rd Reading th Reading th reading th Reading Average = 77.50KV Transformer Oil Curve HV Earth IR Value (MΩs) :00pm 4:00pm 7:00pm 10:00pm 1:00am 4:00am 7:00am 10:00am 1:00pm 4:00pm 7:00pm 10:00pm 1:00am 4:00am 7:00am 10:00am 1:00pm 4:00pm Transformer Oil Curve HV Earth Time 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 75

82 Dehydration, Filtration and Testing of Transformer Oil Transformer Oil Characteristic Curve LV Earth IR Value (MΩs) Transformer Oil Characteristic Curve LV Earth 0 1:00pm 4:00pm 7:00pm 10:00pm 1:00am 4:00am 7:00am 10:00am 1:00pm 4:00pm 7:00pm 10:00pm 1:00am 4:00am 7:00am 10:00am 1:00pm 4:00pm Time Transformer Oil Characteristic Curve HV LV IR Value (MΩs) Transformer Oil Characteristic Curve HV LV 0 1:00pm 4:00pm 7:00pm 10:00pm 1:00am 4:00am 7:00am 10:00am 1:00pm 4:00pm 7:00pm 10:00pm 1:00am 4:00am 7:00am 10:00am 1:00pm 4:00pm Time 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 76

83 Dehydration, Filtration and Testing of Transformer Oil Breakdown values of Transformer Oil with 4mm gap between 13mm diameter spheres. Oil Temp. C BDV KV Courtesy: Installation, commissioning and maintenance of electrical equipment, Tarlok Singh. Conclusion : From the graphical analysis it shows that the IR value decreases, and rise to a stable value thus indicating that the moisture from the core and the oil is removed. Further the BDV test clearly shows that the breakdown voltage is very good. Therefore dehydration and filtration of transformer oil is completed. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 77

84 Winding Resistance and Ratio Check of CT & PT Winding Resistance and Ratio Check of 33kv CT & PT Panel 1 CT (Outgoing Feeder) Panel 2 CT (Outgoing Feeder) Panel 3 CT & PT (Outgoing Feeder) Panel 4 CT (Incomer 2) Panel 5 CT (Bus Coupler) Panel 6 Panel 7 CT (Incomer 1) Panel 8 CT (Outgoing Feeder) Panel 9 CT (Outgoing Feeder) Panel 10 CT (Outgoing Feeder) : /1-1-1A : /1-1-1A : /1-1-1A, 33kV/ 3/110/ 3. : P1: /1-1A & P2: /1-1A, 33kV/ 3/110/ 3 : /1-1A : Adapter Feeder has no CT : P1: /1-1A & P2: /1-1A, 33kV/ 3/110/ 3 : /1-1-1A, 33kV/ 3/110/ 3 : /1-1-1A : /1-1-1A Aim : Testing of Current and Potential Transformer of 33KV side Panel. Objectives : To check the secondary winding resistance of CT and PT To check the ratio of primary to secondary current of various cores under loaded condition and compare with the name plate rating. To check the Insulation Resistance value of Potential Transformer. Theory : Current transformer and Potential Transformer are used for metering and protection. The Current Transformer used here have two ratio i.e. 150/1A and 200/1A. Both the incomers have used the ratio of 200/1A while the outgoing feeders have used 150/1A. The reason being, since the LV current of each Transformer is A each phase will be carrying A therefore keeping the ratio at 400/1A will mar the accuracy that is why 200/1A have been selected as the CT ratio. There are three outgoing feeder for each Transformer which will be carrying the total current from the Transformer. Here too, at the maximum, each feeder will be able to carry a load of A therefore we set the CT ratio to 150/1A instead of 300/1A. However there is every possibility that one feeder may be lightly loaded and the other heavily loaded where by the loading may cross over 150A. For this reason the CT ratio 300/1A should also be checked so that it can be put to use in the above mentioned case. The CT of outgoing feeders has three cores of which core 3 is spare core and has been shorted. CT secondary should never be left open. For the same power when current is stepped down from 300 to 1A, the voltage will rise by that many times. Core 1 has been used for metering while core 2 is used for protection. The incomers have four cores. Core 1 is used for metering, Core 2 for protection, Core 3(PS) is used for Restricted Earth Fault Protection and Core 4 is used for differential protection. Incomers have two CT connected in series, each CT containing two cores thereby four cores in total. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 78

85 Winding Resistance and Ratio Check of CT & PT Instruments Used : Sl. no Description Specification Quantity Remarks 1 Auto Transformer 0-260V, 50Hz 1 2 Loading Transformer 230V,50Hz-7.5KVA, 1V/T 1 3 Multimeter AVΩ meter 1 4 Multimeter Digital Multimeter DM3540A, Motwane 1 5 Clamp leaker DC-10A, Motwane 1 6 Clamp meter Kyoritsu, DCM, Model Connecting wires APR 8 1-Ф Supply 230V, 50Hz 1 Circuit diagram P1 P2 1S1 1S3 2S1 2S3 3S1 3S3 Ωm DMM Pictorial View DMM PT Figure 11 Winding Resistance Check of 33kv CT & PT 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 79

86 Winding Resistance and Ratio Check of CT & PT CT Ratio Check R Y B After giving the supply, measure the current in the ammeter wire and the over current protection panel wire with the help of Clamp Leaker. 1-Ф Supply Figure 12 Ratio Check of 33kv CT Procedure : PART I (Winding Resistance Test) 1. Remove the earth terminal from three phase of PT from the lower side of the box. Make sure there is no connection from the PT to earth. 2. Using the Multi meter as ohmmeter and measure the winding resistance of the respective secondary windings and of respective phases 3. For measuring the winding resistance of CT, connect the multimeter (as ohm meter) terminal to the respective secondary terminals of the Current Transformer. 4. Tabulate the reading and compare with the standard/manufacturer value. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 80

87 Winding Resistance and Ratio Check of CT & PT PART II (Ratio Test) 1. Collect the required instrument for performing the test. 2. Connect the secondary end of the loading transformer to the CT terminals. 3. Connect an Auto transformer (Variac) to provide supply to the loading transformer with varying loading. 4. Connect the Auto Transformer to a single phase supply. 5. Put a Clamp Meter to the wire connecting the CT terminals form the loading transformer. 6. Increase the current in steps of 25%, 50% and 100% of the actual rated current and check the value on the secondary terminals respectively. 7. Repeat step 6, for other ratio too. 8. Repeat step 2-7 for other phases also. Precaution : Safety the first priority. Never leave the secondary terminal of CT open. Always short it if not in use. Make the connections tight. Always remember the approximate value that should come on secondary. If the value doesn t tally then check the connections. Take the readings properly and do not manipulate the reading. Results : The results are being tabulated for each current transformer and potential transformer. The actual ratio given on the name plate are /1-1-1A and /1-1A. The error limits doesn t cross over 15%. Therefore the results are correct. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 81

88 Winding Resistance and Ratio Check of CT & PT PT WINDING RESISTANCE Date:15/10/09, Sunday, Sunny. Panel 3, Outgoing Feeder, Type: OG001 (W013), Breaker rating 1250A. Terminal R: 09/34228 (Ω) Y: 09/34224 (Ω) B: 09/34218 (Ω) 1a-1n a-2n Panel 8, Outgoing Feeder, Type: OG001 (W013), Breaker rating 1250A. Terminal R: 09/34220 (Ω) Y: 09/34227 (Ω) B: 09/34229 (Ω) 1a-1n a-2n Panel 7, Incomer 1, Type: IC002 (W003), Breaker rating 1250A. Terminal R: 09/34221 (Ω) Y: 09/34223 (Ω) B: 09/34225 (Ω) 1a-1n a-2n Panel 4, Incomer 2, Type: IC001 (W008), Breaker rating 1250A. Terminal R: 09/34226 (Ω) Y: 09/34219 (Ω) B: 09/34222 (Ω) 1a-1n a-2n CT WINDING RESISTANCE ( /1-1A) Panel 4, Incomer 2, Type: IC001 (W008), Breaker rating 1250A, 17/11/09. P2 Terminal R: 09/24606 (Ω) Y: 09/24607 (Ω) B: 09/24609 (Ω) 1S1-1S S1-1S S1-2S S1-2S P1 Terminal R: 09/24602 (Ω) Y: 09/24603 (Ω) B: 09/24601 (Ω) 1S1-1S S1-1S S1-2S S1-2S Panel 7, Incomer 1, Type: IC002 (W003), Breaker rating 1250A. P2 Terminal R: 09/24611(Ω) Y: 09/24608 (Ω) B: 09/24610 (Ω) 1S1-1S S1-1S S1-2S S1-2S P1 Terminal R: 09/24604(Ω) Y: 09/24605 (Ω) B: 09/24597 (Ω) 1S1-1S S1-1S S1-2S S1-2S KV/33KV, Olakha Sub Station, Thimphu. Page 82

89 Winding Resistance and Ratio Check of CT & PT CT WINDING RESISTANCE ( /1-1-1A) Date: 17/11/2009, Tuesday, Sunny. Panel 1, Outgoing Feeder, Type: OG002 (W013), Breaker rating 1250A. Terminal R: 09/24596(Ω) Y: 09/24580 (Ω) B: 09/24590 (Ω) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-1S Panel 2, Outgoing Feeder, Type: OG002 (W013), Breaker rating 1250A. Terminal R: 09/24583 (Ω) Y: 09/24579 (Ω) B: 09/24585 (Ω) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-1S Panel 3, Outgoing Feeder, Type: OG001 (W013), Breaker rating 1250A. Terminal R: 09/24582 (Ω) Y: 09/24593 (Ω) B: 09/24594 (Ω) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-1S Panel 5, Bus Coupler, Type: BC001 (W013), Breaker rating 1250A. Terminal R: 09/24600 (Ω) Y: 09/24599 (Ω) B: 09/24598 (Ω) 1S1-1S S1-1S S1-2S S1-2S Panel 8, Outgoing Feeder, Type: OG001 (W013), Breaker rating 1250A.17/11/09. Terminal R: 09/24592 (Ω) Y: 09/24591 (Ω) B: 09/24586 (Ω) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-1S KV/33KV, Olakha Sub Station, Thimphu. Page 83

90 Winding Resistance and Ratio Check of CT & PT Panel 9, Outgoing Feeder, Type: OG002 (W013), Breaker rating 1250A.17/11/09. Terminal R: 09/24581 (Ω) Y: 09/24587 (Ω) B: 09/24595 (Ω) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-1S Panel 10, Outgoing Feeder, Type: OG002 (W013), Breaker rating 1250A.17/11/09. Terminal R: 09/24589 (Ω) Y: 09/24584 (Ω) B: 09/24588 (Ω) 1S1-1S S1-1S S1-2S S1-2S S1-3S S1-1S Primary (V) PT RATIO CHECK (33kV/ 3/110/ 3) Date:15/10/09, Sunday, Sunny. Panel 4, Incomer 2, Type: IC001, Breaker rating 1250A. Sl. No. R: 09/34228, Y: 09/34224, B: 09/34218 Secondary (V) R-Phase Y-Phase B-Phase Core1 Core2 Core1 Core2 Core1 Core Ratio % Error Panel 3, Outgoing Feeder, Type: OG001 (W013), Breaker rating 1250A. Sl. No. R: 09/24582, Y: 09/24593, B: 09/24594 Primary (V) Secondary (V) R-Phase Y-Phase B-Phase Core1 Core2 Core1 Core2 Core1 Core Ratio % Error Panel 7, Incomer 1, Type: IC002, Breaker rating 1250A. Sl. No. R: 09/24611, Y: 09/24608, B: 09/24610 Primary (V) Secondary (V) R-Phase Y-Phase B-Phase Core1 Core2 Core1 Core2 Core1 Core Ratio % Error KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 84

91 Winding Resistance and Ratio Check of CT & PT Panel 8, Outgoing Feeder, Type: OG001, Breaker rating 1250A. Sl. No. R: 09/24592, Y: 09/24591, B: 09/24586 Secondary (V) Primary (V) R-Phase Y-Phase B-Phase Core1 Core2 Core1 Core2 Core1 Core Ratio % Error CT RATIO CHECK Panel 1 CT Station Feeder, 1S1-1S2, 150/1A: Metering. Date: 24/11/2009, Tuesday, Sunny. R-Sl.no. 09/24596, Y-Sl.no. 09/24580, B-Sl.no. 09/24590 Secondary Current (A) R-phase Y-phase B-phase (A) Ratio % error (A) Ratio % error (A) Ratio % error % % % % % % % % % Panel 1 CT, 2S1-1S2, 150/1A: Protection % % % % % % % % % Panel 2 CT Outgoing Feeder, 1S1-1S2, 150/1A: Metering. R-Sl.no. 09/24583, Y-Sl.no. 09/24579, B-Sl.no. 09/ % % % % % % % % % Panel 2 CT, 1S1-1S3, 300/1A: Not Used % % % % % % % % % Panel 2 CT, 2S1-1S2, 150/1A: Protection % % % % % % % % % Panel 2 CT, 2S1-2S3, 300/1A: Not Used % % % % % % % % % Panel 3 CT Outgoing Feeder, 1S1-1S2, 150/1A: Metering. R-Sl.no. 09/24583, Y-Sl.no. 09/24579, B-Sl.no. 09/ % % % % % % % % % Applied Primary Current (A) 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 85

92 Winding Resistance and Ratio Check of CT & PT Panel 3 CT, 1S1-1S3, 300/1A: Not Used % % % % % % % % % Panel 3 CT, 2S1-1S2, 150/1A: Protection % % % % % % % % % Panel 3 CT, 2S1-2S3, 300/1A: Not Used % % % % % % % % % Panel 4 CT Incomer 2, 1S1-1S2, 200/1A: Metering. P1 R-Sl.no. 09/24602, Y-Sl.no. 09/24603, B-Sl.no. 09/24601 P2 R-Sl.no. 09/24606, Y-Sl.no. 09/24607, B-Sl.no. 09/ % % % % % % Panel 4 CT, 1S1-1S3, 400/1A: Not Used % % % % % % % % % Panel 4 CT, 2S1-1S2, 200/1A: Protection % % % % % % Panel 4 CT, 2S1-2S3, 400/1A: Not Used % % % % % % % % % Panel 4 CT, 3S1-3S2, 200/1A: REF % % % % % % Panel 4 CT, 3S1-3S3, 400/1A: Not Used % % % % % % % % % Panel 4 CT, 4S1-4S2, 200/1A: Differential Protection % % % % % % Panel 4 CT, 4S1-4S3, 400/1A: Not Used % % % % % % % % % 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 86

93 Winding Resistance and Ratio Check of CT & PT Panel 5 CT Bus Coupler, 1S1-1S2, 200/1A: Metering. R-Sl.no. 09/24600, Y-Sl.no. 09/24599, B-Sl.no. 09/ % % % % % % Panel 5 CT, 1S1-1S3, 400/1A: Not Used % % % % % % % % % Panel 5 CT, 2S1-1S2, 200/1A: Protection % % % % % % Panel 5 CT, 2S1-2S3, 400/1A: Not Used % % % % % % % % % Panel 7 CT Incomer 1, 1S1-1S2, 200/1A: Metering. P1 R-Sl.no. 09/24604, Y-Sl.no. 09/24605, B-Sl.no. 09/24597 P2 R-Sl.no. 09/24611, Y-Sl.no. 09/24608, B-Sl.no. 09/ % % % % % % Panel 7 CT, 1S1-1S3, 400/1A: Not Used % % % % % % % % % Panel 7 CT, 2S1-1S2, 200/1A: Protection % % % % % % Panel 7 CT, 2S1-2S3, 400/1A: Not Used % % % % % % % % % Panel 7 CT, 3S1-3S2, 200/1A: REF % % % % % % Panel 7 CT, 3S1-3S3, 400/1A: Not Used % % % % % % % % % Panel 7 CT, 4S1-4S2, 200/1A: Differential Protection % % % % % % KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 87

94 Winding Resistance and Ratio Check of CT & PT Panel 7 CT, 4S1-4S3, 400/1A: Not Used % % % % % % % % % Panel 8 CT Outgoing Feeder, 1S1-1S2, 150/1A: Metering. R-Sl.no. 09/24592, Y-Sl.no. 09/24591, B-Sl.no. 09/ % % % % % % % % % Panel 8 CT, 1S1-1S3, 300/1A: Not Used % % % % % % % % % Panel 8 CT, 2S1-1S2, 150/1A: Protection % % % % % % % % % Panel 8 CT, 2S1-2S3, 300/1A: Not Used % % % % % % % % % Panel 9 CT Outgoing Feeder, 1S1-1S2, 150/1A: Metering. R-Sl.no. 09/24581, Y-Sl.no. 09/24587, B-Sl.no. 09/ % % % % % % % % % Panel 9 CT, 1S1-1S3, 300/1A: Not Used % % % % % % % % % Panel 9 CT, 2S1-1S2, 150/1A: Protection % % % % % % % % % Panel 9 CT, 2S1-2S3, 300/1A: Not Used % % % % % % % % % 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 88

95 Winding Resistance and Ratio Check of CT & PT Panel 10 CT Outgoing Feeder, 1S1-1S2, 150/1A: Metering. R-Sl.no. 09/24589, Y-Sl.no. 09/24584, B-Sl.no. 09/ % % % % % % % % % Panel 10 CT, 1S1-1S3, 300/1A: Not Used % % % % % % % % % Panel 10 CT, 2S1-1S2, 150/1A: Protection % % % % % % % % % Panel 10 CT, 2S1-2S3, 300/1A: Not Used % % % % % % % % % INSULATION RESISTANCE CHECK OF PT IR Check of Incomer 2 PT, Panel 4 (1kV Megger), MΩ Phase Pry-Earth Pry-Sec1 Pry-Sec2 Sec1-Sec2 Sec1-Earth Sec2-Earth R Y B IR Check of Incomer 1 PT, Panel 7 (1kV Megger), MΩ Phase Pry-Earth Pry-Sec1 Pry-Sec2 Sec1-Sec2 Sec1-Earth Sec2-Earth R Y B IR Check of Outgoing Feeder, Panel 8 (1kV Megger), MΩ Phase Pry-Earth Pry-Sec1 Pry-Sec2 Sec1-Sec2 Sec1-Earth Sec2-Earth R Y B IR Check of Outgoing Feeder, Panel 3 (1kV Megger), MΩ Phase Pry-Earth Pry-Sec1 Pry-Sec2 Sec1-Sec2 Sec1-Earth Sec2-Earth R Y B KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 89

96 Winding Resistance and Ratio Check of CT & PT IR Check of 33kV Circuit Breaker, Panel 1 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B IR Check of 33kV Circuit Breaker, Panel 2 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B IR Check of 33kV Circuit Breaker, Panel 3 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B IR Check of 33kV Circuit Breaker, Panel 4 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B IR Check of 33kV Circuit Breaker, Panel 5 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B IR Check of 33kV Circuit Breaker, Panel 7 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B IR Check of 33kV Circuit Breaker, Panel 8 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B IR Check of 33kV Circuit Breaker, Panel 9 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B IR Check of 33kV Circuit Breaker, Panel 2 (Motorized 5kV Megger), MΩ Phase Upper arm - Earth Lower arm - Earth Upper arm - Lower arm R Y B KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 90

97 Winding Resistance and Ratio Check of CT & PT Conclusion : From this field test, it confirms that the secondary winding resistances are within its permissible value. The CT and PT Ratio also match with the name plate rating. The Insulation Resistance value also shows good insulation. The CT ratios have been checked for every core and for both the ratio. Thus we hereby conclude that the equipment has no defect and can be put to use. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 91

98 Testing of XLPE Cables (High POT Test) HIGH POT TEST (CABLE HV TEST) Aim : Testing of XLPE Cables. Objective : To check the Insulation Resistance Value of the cables. To check the withstand voltage of the cable. To check the value of leakage current flowing out from the cable to ground. Theory : High POT Test or Cable HV Test or High Pressurized Test, anyone one may say but all these are same. Such tests are performed to know the IR value of the insulation and the leakage current flowing into the ground. This test can be done with AC as well as DC. In fact this test should be done with AC but wherever possibility doesn t exist we go for DC supply. This test will also confirm whether the cable will be able to withstand the desired voltage. Cables have a capacitive effect so when we apply AC voltage, it will allow the current the pass through without any hindrance but blocks the DC therefore the current will be quite high (in terms of amperes), so such current will trip. But the testing kit is meant to measure current in terms of miliamperes. If we go for DC then the current required for charging the capacitor will be very less which tallies with our testing kit. Therefore we convert the AC supply to DC supply with the help of Rectifier and the current limiting resistor and supply the voltage. DC voltage is root 2 times the AC voltage. Since the capacitor remains charged once the voltage is applied it is necessary to discharge the capacitor after finishing the experiment in order to avoid shock. Discharge it to ground with discharge rod. While doing for Bus Section we use AC voltage since here we do not have capacitive effect. The conductors are rectangular copper plates. If dust and moisture is present then the spark will occur before actual withstand voltage is applied. In such case we will have to clean and heat the surrounding of the conductor and then do the test. While doing the experiment one may notice that the pointer of the AVΩ meter keeps on fluctuating indicating the presence of dust. As we increase the voltage beyond 30KV, hissing sound occurs indicating the inception of Corona. While increasing the voltage the air around the conductor also gets ionized and if moisture is present around then the voltage gets discharged through the conducting medium (moisture) to the ground. While discharging the cable after the test, if the discharge is high then it indicates the capacitive effect is more indicating longer cables thereby more leakage and weaker insulation. Better the insulation and shorter the length of the cable, lesser will be the discharge (spark). The leakage current should be within 10-15mA. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 92

99 Testing of XLPE Cables (High POT Test) Instruments Used : Sl. No. Description Specification Remarks 1 HV Testing Transformer I/p: 0-250V, O/p: 0-36KV, Prayog Electricals 1-Ф, 50Hz, Sl. no. H Pvt. Ltd. Bombay 2 Rectifier Sl. no. H Current limiting Resistor 4 High Voltage Tester I/p: 220/250V, O/p: 0-36KV, Prayog Electricals 1-Ф, 50Hz, Sl. no. H Pvt. Ltd. Bombay 5 Motorized Megger 5kV, AC input. 6 AVΩ Meter µa and ma range Experimental diagram : B Y R Current Limiting Resistor Rectifier High Voltage Transformer 1 Ф Supply E High Voltage Tester 1 Ф Supply AVΩ Meter Figure 13 High POT Test (CABLE HV TEST) 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 93

100 Testing of XLPE Cables (High POT Test) Procedure : PART I (Before HV Test) 1. Collect the required testing instrument as per the requisition table. 2. Clean thoroughly the dust and dirt from the conductors to be tested and heat the area so that the place is moisture free. 3. Connect Megger to R-earth phase and supply the power. Note the value of resistance after reaching a steady value. 4. Repeat step 2 for Y phase and B phase. 5. Check the Megger value for phase to phase. PART II 1. Short any two phases (say Y & B) with earth terminal. Leave the other phase (say R) unconnected. 2. Connect the terminal from the HV Transformer to R phase. 3. Switch on the power supply. 4. Gradually increase the voltage up to 40kV DC and keep it for 5 minutes. 5. Check the leakage current in the ammeter connected to the HV Transformer. 6. Note down the reading. 7. Repeat step 1-6 Y and B phase too. 8. For Bus section where bare conductors is there, use AC voltage for 1 minute. PART III 1. After completing Part I & II, then Connect Megger to R-earth phase and supply the power. 2. Observe the IR value after the meter pointer attains a steady value. 3. Connect Megger to Y-Earth and supply the power. 4. Repeat step 3 for B-Earth terminals. 5. Check the Megger value for phase to phase i.e. R-Y, Y-B & B-R. 6. Note down the readings carefully. Precautions : 1. Safety the first priority. 2. When high voltage is being injected don t allow anyone to stand nearby the testing kit. 3. Make sure no one is there on the equipment on which test is being carried out. 4. Forget not, to keep one person guarding the other end of cable so that no one comes nearby the cable under test. 5. Always increase the voltage gradually. If sparking occurs, it is due to moisture and dust, so make the area clean and dry. 6. After completing the test always discharge the charge from the cable with the help of discharge rod before touching it with bare hand. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 94

101 Testing of XLPE Cables (High POT Test) HIGH POT TEST (CABLE HV TEST): Cable between Transformer 1 and 33kV Panel 7. Date: 26/11/2009, 10:40am, Location: Inside the room. Temperature : 12 C IR Check of Cable ( 5KV Motorized Megger) Terminals Before HV Test (MΩ) After HV Test (MΩ) R-Earth Y-Earth B-Earth R-Y Phase Y-B Phase B-R Phase KV DC applied to the Cable under Test for 5 minutes Terminals Leakage Current (µa) R- Y+B+Earth 10 Y- R+B+Earth 10 B- Y+R+Earth 10 HIGH POT TEST (CABLE HV TEST): Cable between Transformer 2 and 33kV Panel 4. Date: 26/11/2009, Location: Inside the room. Temperature : 12 C IR Check of Cable ( 5KV Motorized Megger) Terminals Before HV Test (MΩ) After HV Test (MΩ) R-Earth Y-Earth B-Earth R-Y Phase Y-B Phase B-R Phase KV DC applied to the Cable under Test for 5 minutes Terminals Leakage Current (µa) R- Y+B+Earth 10 Y- R+B+Earth 7 B- Y+R+Earth 37 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 95

102 Testing of XLPE Cables (High POT Test) HIGH POT TEST (CABLE HV TEST): Outgoing Cable from Panel 1. Date: 26/11/2009, 11:30am, Location: Inside the room. Temperature : 13 C IR Check of Cable ( 5KV Motorized Megger) Terminals Before HV Test (MΩ) After HV Test (MΩ) R-Earth Y-Earth B-Earth R-Y Phase Y-B Phase B-R Phase KV DC applied to the Cable under Test for 5 minutes Terminals Leakage Current (µa) R- Y+B+Earth 10 Y- R+B+Earth 10 B- Y+R+Earth 10 BUS TEST (100X10 SQ.MM) SECTION 2 Date: 26/11/2009, Location: Inside the room. IR Check of Bus, Section 2 ( 5KV Motorized Megger) Terminals Before HV Test (MΩ) After HV Test (MΩ) R-Earth Y-Earth B-Earth R-Y Phase Y-B Phase B-R Phase KV AC applied to the Bus under Test for 1 minute. Terminals Leakage Current (ma) R- Y+B+Earth 2 Y- R+B+Earth 2 B- Y+R+Earth 2 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 96

103 Testing of XLPE Cables (High POT Test) BUS TEST (100X10 SQ.MM) SECTION 1 Date: 26/11/2009, Location: Inside the room. IR Check of Bus, Section 1 ( 5KV Motorized Megger) Terminals Before HV Test (MΩ) After HV Test (MΩ) R-Earth Y-Earth B-Earth R-Y Phase Y-B Phase B-R Phase KV AC applied to the Bus under Test for 1 minute. Terminals Leakage Current (ma) R- Y+B+Earth 3 Y- R+B+Earth 5 B- Y+R+Earth 4 (Trip at 30kV) HIGH POT TEST (CABLE HV TEST): Outgoing Cable from Panel 9. Date: 16/12/2009, 4:45pm, Location: Inside the room. Temperature : 13 C IR Check of Cable, 3x150sq.mm. ( 5KV Motorized Megger) Terminals Before HV Test (MΩ) After HV Test (MΩ) R-Earth Y-Earth B-Earth R-Y Phase Y-B Phase B-R Phase KV DC applied to the Cable under Test for 5 minutes Terminals Leakage Current (µa) R- Y+B+Earth 8 Y- R+B+Earth 8 B- Y+R+Earth 6 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 97

104 Testing of XLPE Cables (High POT Test) HIGH POT TEST (CABLE HV TEST): Outgoing Cable from Panel 8. Date: 16/12/2009, Location: Inside the room. Temperature : 13 C IR Check of Cable, 3x150sq.mm. ( 5KV Motorized Megger) Terminals Before HV Test (MΩ) After HV Test (MΩ) R-Earth Y-Earth B-Earth R-Y Phase Y-B Phase B-R Phase KV DC applied to the Bus under Test for 5 minutes. Terminals Leakage Current (µa) R- Y+B+Earth 4 Y- R+B+Earth 15 B- Y+R+Earth 15 HIGH POT TEST (CABLE HV TEST): Outgoing Cable from Panel 2. Date: 16/12/2009, Location: Inside the room. Temperature : 13 C IR Check of Cable, 3x150sq.mm. ( 5KV Motorized Megger) Terminals Before HV Test (MΩ) After HV Test (MΩ) R-Earth Y-Earth B-Earth R-Y Phase Y-B Phase B-R Phase KV DC applied to the Bus under Test for 1 minute. Terminals Leakage Current (µa) R- Y+B+Earth 6 Y- R+B+Earth 8 B- Y+R+Earth 10 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 98

105 Testing of XLPE Cables (High POT Test) Observation : While the experiment is under test, one will observe the inception of corona above 30kV/cm 2. Hissing sound will be noticed indicating the inception of corona. Some sparking sound may be heard indicating the presence of dust particles. If moisture is present then the voltage trips off through spark before reaching the set voltage as it happened for B-phase of Bus Section 1. So we heated the area with halogen lamp, cleaned the conductor thoroughly and performed the test which gave better result. While Meggering, initially the pointer moves towards zero indicating the capacitance of the cable being charged i.e. the current is drawn to charge the capacitance of the cable so no current flows through the cable. However after the capacitive effect of the cable, the current passes through cable thus indicating the IR value. For Long cables the pointer may stick at zero for longer time indicating greater capacitance however the pointer will rise slowly. Conclusion : The result shows very good IR value of the cable and bus section. The leakage current found is very less ranging in micro amperes while the normal leakage current comes in 10-15mA. For better result the conductors should be free from dust particles and moisture free. However our results have good IR values and lesser leakage current indicating the stability of cable under the desired voltage. Therefore the cables are good and healthy. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 99

106 Inverse Definite Minimum Time (IDMT) Relay Test Relay Testing (Over Current Protection) Aim : Testing of Inverse Definite Minimum Time (IDMT) and Earth Fault Relay of 33KV Vacuum Circuit Breaker. Objective : Find out the trip time of IDMT Relay under Normal condition. Find out the trip time of IDMT Relay under High Set condition. Find out the trip time of Earth Fault IDMT under Normal Condition. Find out the trip time of Earth Fault IDMT under High Set Condition. Theory : An over current protection device protects the circuit by opening the device when the current reaches a value that will cause an excessive or dangerous temperature rise in conductors. The time it takes for an over current protection device (OCPD) to open is inversely proportional to the magnitude of the fault current. Thus, the higher the ground-fault current, the less time it takes for the OCPD to open and clear the fault. Inverse Definite Minimum Time Over current (IDMT) relay gives inverse-time current characteristics at lower values of the fault current and definite-time characteristics at higher values of the fault current (Used in distribution line). Here we set the current and Trip time at a particular value and then injects higher current and note the Trip time obtained. The field test should confirm that the trip time obtained should not be greater than the set time. According to British standards, the following are the important characteristics of over current relays. Figure 14 Inverse-Time, Very-Inverse Time and Extremely-Inverse Time characteristics. 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 100

107 Inverse Definite Minimum Time (IDMT) Relay Test Instruments Used : Sl. no Description Specification Quantity Remarks 1 Relay Test Set 230V, 50Hz, A, Shruti Electronics S, S Kolkata 2 Clamp Leaker DC-10A, Motwane 1 3 Connecting Wires APR 4 Power Supply 230V, 50Hz 1 Circuit Diagram: X1 TB R=15, Y=19, B=23, N=27 Back View of the Relay. Connected in order to check the time from the relay test set as well as Power Supply Figure 15 Testing of IDMT Relays 66KV/33KV, Olakha Sub Station, Thimphu. Chering6875@msn.com Page 101