Case Study 38 Reduction in Break Down and Specific Energy Consumption by Reducing Harmonics at Usha Martin Wire Rope Plant.

Transcription

1 CS 38 ENRG 14 Reduction in Break Down and Specific Energy Consumption by Reducing Harmonics at a Steel Wire Rope Plant APQI (C) Copyright (2013) All Rights Reserved 1

2 target of reducing energy consumption that they have to meet by Abstract: Energy Conservation Act 2001 provides a legal framework to embarking on energy conservation in India. Under the act government classified industries based on energy consumption and these industries are known as Designated Consumer (DC). These DC s are covered under Perform Achieve and Trade (PAT) mechanism with total energy saving target of 6.6 Million Tonnes of Oil Equivalent by All designated consumers are provided with Reduction in energy consumption is one of the priorities of these DC s. Operating the plant without many breakdowns is one of the top priorities for any manufacturing facility. Increased breakdown causes production loss, higher specific energy consumption and reduced profit margins. With use of drives, AC to DC convertors and SMPS loads, generation of harmonics is inevitable. These harmonic current can cause unexpected break downs and loss of energy due to additional heat generation in cables, motors and transformers. The Case study below presents how a steel wire rope mill reduced specific energy consumption and breakdowns by filtering out harmonics. APQI (C) Copyright (2013) All Rights Reserved 2

3 Introduction Usha Martin is India s largest and world s second largest steel wire rope manufacturers. Manufacturing of steel wire involves number of DC motors and AC to DC convertors. Wire bars are used to make wire ropes.manufacturing of wire rod uses iron ore as a raw material and it passes through different process of extracting iron from the iron ore. Wire rod is used as a raw material to manufacture wire rope. Schematic diagram -1 below shows production process of steel wire rope. Diagram 1 Wire Rope production process Transformation of wire rod in wire rope involves drawing and stranding to increase the length of the wire rod and decrease its diameter. Surface treatment, galvanising and patenting process are adopted during the making of wire rope to change surface properties of the metal. In the process of drawing and stranding number of motors with different capacities are used. Failure of one motor in drawing or stranding section can cause stoppage of production line and loss in productivity. All these motors are equipped with drives to control speed of the mill. Failure in drives or control cards will also reduce productivity. In above manufacturing process various drives present in wire rope mill produces harmonics. Presence of harmonics in the system can cause problems like: 1. Additional heat generation in the cables and neutral 2. Increase failure rate of electrical and electronics equipment 3. Increased energy consumption due to increased losses 4. Nuisance tripping of circuit breaker APQI (C) Copyright (2013) All Rights Reserved 3

4 Background The production facility was facing problems of breakdown of various electrical and electronic equipments. Various type of problems and failure in the plant as reported were as below. A) Electronic Card Failures listed below starting with the most frequent failures. 1. VFD master drive control card (CUVC), a) Control Card b) Power card including SMPS and IGBT 2. DC motor field controller card 3. DC motor field controller card with Thyristors 4. AC Drive Card a) Controller card b) Power card including SMPS and IGBT 5. DC Drive Card a) Controller card b) Power card including SMPS and IGBT 6. PLC and MMI a) CPU card b) MMI controller card c) MMI display card B) Motor Failures details and types of motor failureslisted below. 1. DC Motors. The plant has 5 to 200kw motors and out of which maximum failure happen for 5kw to 80kw motors. a) Commutator uneven surface grooving and increased gap between slots b) Bearing wear-out and failure in the bearing-sitting-shaft and bearing-housing at motor end cover. c) Field winding overheat, insulation puncture and interlayer short-circuit d) Armature insulation puncture i. Equalizer winding in commutator ii. Inter-pole winding in between field winding iii. Armature winding in slot. APQI (C) Copyright (2013) All Rights Reserved 4

5 2. Squirrel Cage IM. The plant has FHP to 315kw motors and out of which maximum failure happen for 5kw to 80kw motors. a) Bearing wear-out and failure in the bearing-sitting-shaft and bearing-housing at motor end cover and bearing cage damage. b) Stator winding insulation puncture c) Rotor Bar, melt open, happens occasionally and up to 11kw motors only. 3. Slip Ring IM. The plant has 18.5 to 110kw motors and out of which maximum failure happen for 18.5kw to 55kw motors. a) Bearing wear-out and failure in the bearing-sitting-shaft and bearing-housing at motor end cover and bearing cage damage. b) Stator winding insulation punctures. c) Rotor winding insulation punctures. d) Slip ring uneven surface grooving and increased gap between slots C) List of Card/Motor/SWG. Failures and Nuisance Tripping. Table -1 below shows different types of breakdowns occurring in the plant along with their frequency according to feeder transformer. TRF Load Process Mfg. Line Nuisance Tripping Per 8-hr. Shift Card Failure Per Month Motor Failure Per Month SWG. Failure Per Year 1. 1x3mva TRF-5 Wire Mill x1mva TRF-1&2 2. 3x1mva TRF-3,4,5 3. 2x1mva TRF-6&8 Wire Mill x3mva TRF x1mva TRF-7&9 Wire Mill x3mva TRF x3mva TRF-7&8 3. 1x3mva TRF x1mva TRF-7&9 Ropery 1-per day x1mva TRF-1&2 SPD 1-per day 2-year Table-1 Breakdown rate APQI (C) Copyright (2013) All Rights Reserved 5

6 In order to find reason behind above mentioned breakdown and failure, the plant management carried out a detailed harmonic study of the plant. Harmonic levels were measured at different locations in the plant. Table-2 below shows summary of harmonic level at incomer level and different feeders in the plant. Date / Load 3-Ph Voltage KV/volt 3-Ph Current ~ Max %-THD-v MW-pk. MVAr-pk. PF-ave. Ref page in annex-ii & CTR %-THD-i MW-ave. MVAr-ave. Hz-ave. Remarks (Harmonics) * 33kv Power Source JSEB Incomer and 10mw CPP 33kv JSEB I/C % 45.0% 5 th, 7 th, 3 rd * High Harmonics from Loads 33kv CPP I/C TRF-4 Ropery TRF-5 Wire Mill TRF-7 LRPC Ropery TRF-8 LRPC Ropery TRF-10 HRBC Ropery& Wire Mill TRF-1,2 Main SS Wire Mill TR-3,4,5 Main SS Wire Mill % 7.0% 5 th, 7 th, 3 rd 12% 21% 7 th, 5 th, 3 rd 15% 60% 5 th, 7 th, 3 rd 11% 37% 5 th, 7 th, 11 th 10% 36% 5 th, 7 th, 3 rd 12% 35% 5 th, 7 th * 3mva, 33/0.415kv TRF Load Distributions % 33% 5 th, 7 th, 11 th 11% 22% 5 th, 7 th, 11 th * 1mva, 11/0.415kv TRF Load Distributions Table-2Harmonic level at different feeders * Harmonics are within near Limits * High Harmonics from Loads * 500/1400 =35% Cap effective * In=500A, I3=25% of In * High Harmonics from Loads * 800/1600=50% Cap effective * I/C-1 (x2) & I/C (x1) LF adjusted * High Harmonics from Loads * 1 of 2 LRPC lines were OFF * 400/400=100% Cap effective * High Harmonics from Loads * Ducati Cap burnt & removed * High Harmonics from Loads * 200/600=33% Cap effective * 3mva, 11/0.415kv TRF from Main SS * High Harmonics from Loads * 300/600=50% Cap effective * High Harmonics from Loads * Cap ON throughout APQI (C) Copyright (2013) All Rights Reserved 6

7 Table-3 below shows IEEE-519 standard. a1) Current Harmonic Distortion (120V- 69kV) User s responsibility I SC / I1 < 11 11<=h<1 17<=h<23 23<=h<35 35<= h THD 7 <20 * < < < > Notes The best harmonic management practice is to limit it at lowest possible volt level at its point of generations. Also user PCC at TRF secondary is always <69kv. a2) Voltage Harmonic Distortion TRF Sec volt; its user s responsibility Bus voltage at Individual voltage THD Remarks PCC distortion <=69 KV 69>=161 KV >161 KV Table-3 IEEE-519 Standard HV system may have up to 2% THD, as in HVDC terminal that attenuates while tapped for a user. Notes on IEEE-519 Standard: * All power generation equipments are limited with these limits regardless of their I SC /I1 value. Odd Harmonics (I3, 5 ): Values in table are for odd harmonic limits as % of I1. Even Harmonics (I2, 4 ): Even harmonics are limited to 25% of odd harmonic limits. I SC : Short Circuit current at PCC at system fault MVA. If I SC =32kA at 3.3kv & I1=1.487kA then 8% THD limit apply. I1: Fundamental Full Load Current at PCC. If Grid IC TRF is 8.5mva 110/3.3kv; I1 =1.487kA at 3.3kv. Harmonic Number (I5, I7 ) THD Total Harmonic Distortion; say THDi (current) or THDv (voltage) When measured values were compared with the IEEE-519 standard, it was found that at all distribution transformers, harmonic current were higher than the limit prescribed by the standard. The load consists of drives, PLC s and AC to DC convertors and as seen from table 2 above, harmonics were recorded at all distribution transformers due to non linear load. As harmonics have a tendency to flow in the upstream of the network due to low impedance, harmonics were found at the grid incomer. The flow of harmonics is towards the grid and can flow in the system of other plant connected on the same grid. After carrying out the study, the top management decided to install passive harmonic filter at the different locations as suggested by the auditor. Usha Martin took the project to install passive harmonic filters in a phased manner. APQI (C) Copyright (2013) All Rights Reserved 7

8 Solution adopted by the plant: From the study, it came to knowledge of the plant team that the harmonic levels at different feeder levels are very high as compared to limit specified by IEEE-519. One of the very possible reasons for failure of various components in the plant could be presence of harmonics. The plant team decided to mitigate harmonics by installing harmonic filter. As the order of harmonics were same for a feeder and loading conditions were almost constant, the plant team decided to install passive harmonic filter. The passive harmonic filters were designed as per load current and order of harmonics. The plant team decided to install passive harmonic filter in a phased manner. In the first phase, the plant team installed passive harmonic filter on transformer number 4 and transformer number 5 where presence of harmonics were maximum. Rating of the installed harmonic filter is as below. Transformer 4 (1x3mva, 33kv/ 0.415kv): Passive Tuned Harmonic Filter; 2365A (incl. 30% overload) 415v, 50 Hz 3840kvar. Tuned at 5th/7th to limit THD-v & THD-i Transformer 5 (1x3mva, 33kv/ 0.415kv):Passive Tuned Harmonic Filter; 3422A (incl. 30% overload) 415v, 50 Hz 5760kvar. Tuned at 5 th /7 th to limit THD-v & THD-i The plant installed these filters in the month of May In order to assess benefits gained by the installing harmonic filter at transformer 4 and transformer 5, plant team carried out detailed analysis. The analysis was carried out for: 1. Effect on breakdown 2. Effect on energy consumption 3. Effect on production and specific energy consumption Post Mitigation Analysis Effect on harmonics: After installation of passive harmonic filter at transformer 4 and transformer 5, the plant team carried out measurement at the above mentioned feeders. Table 4 gives summary of APQI (C) Copyright (2013) All Rights Reserved 8

9 comparison of harmonic level measured at transformer 4 and 5 with and without harmonic filter. Without Harmonic filter With Harmonic Filter Location Vthd Ithd Vthd Ithd Transformer 4 12% 21% 2.10% 11.20% Transformer 5 15% 60% 1.20% 7.20% Table-4 Voltage and Current THD comparison Transformer - 4 Figure -3A and 3B shows snapshots of voltage waveform and harmonic levels measured without and with harmonic filter at transformer 4. From the snapshot it can be seen that without harmonic filter the waveform is distorted where as with harmonic filter the waveform is more of sinusoidal nature with lower level of voltage distortion. Figure 3A Vthd and Voltage waveform without harmonic filter at TR-4 APQI (C) Copyright (2013) All Rights Reserved 9

10 Figure 3B Vthd and Voltage waveform with harmonic filter at TR-4 Figure -4A and 4B showssnapshots of current waveform and harmonic levels measured without and with harmonic filter at transformer 4. From the snapshot it can be seen that without harmonic filter the waveform is distorted where as with harmonic filter the waveform is more of sinusoidal nature with lower level of current distortion. Graph 4B shows that 5 th order harmonics increased, however graph 4A has maximum value of THD up to 40% where as graph 4B has maximum value of THD up to 20%. Figure 4A Ithd and current waveform without harmonic filter at TR-4 APQI (C) Copyright (2013) All Rights Reserved 10

11 Figure 4B Ithd and current waveform with harmonic filter at TR-4 Transformer - 5 Figure -5A and 5B shows snapshots of voltage waveform and voltage harmonic levels measured without and with harmonic filter at transformer 5. From the snapshot it can be seen that without harmonic filter the waveform is distorted where as with harmonic filter the waveform is more of sinusoidal nature with lower level of voltage distortion. Figure 5A Vthd and voltage waveform without harmonic filter at TR-5 APQI (C) Copyright (2013) All Rights Reserved 11

12 Figure 5B Vthd and voltage waveform with harmonic filter at TR-5 Figure -6A and 6B shows snapshots of current waveform and current harmonic levels measured without and with harmonic filter at transformer 5. From the snapshot it can be seen that without harmonic filter the waveform is distorted where as with harmonic filter the waveform is more of sinusoidal nature with lower level of voltage distortion. Figure 6A Ithd and current waveform without harmonic filter at TR-5 APQI (C) Copyright (2013) All Rights Reserved 12

13 Figure 6B Ithd and current waveform with harmonic filter at TR-5 Effect on breakdown: Table -4 shows comparison of failure rate of different component in the plant before and after installation of harmonic filter. Component Ratings FY 13 APR 13 MAY 13 JUN 13 JUL 13 AUG 13 SEP 13 OCT 13 NOV 13 No of Motors Failed No of Drives Failed No of PLCs Failed Before HF Component Failure Trend After HF < 3 KW KW KW KW >25 KW Total < 1 KW KW > 11 KW Total < 1 KW KW > 11 KW Total Table 4 Breakdown Before and after installation of harmonic filter APQI (C) Copyright (2013) All Rights Reserved 13

14 Table 5 shows change in annual rate of failure before and after installation of harmonic filter. Component Annual failure rate before Harmonic filter FY June- Nov 2013 Failure s Extrapolated - Annual failure rate after harmonic filter Change in failure rate Motors % Reduced by 81% Drives % Reduced by 85% Decreased by PLC's % 64% Table-5 Breakdown rate Before and after harmonic filter From table 4 and 5 it can be seen that after installation of harmonic filter, there is significant reduction in breakdown of different component. Each break down result in loss of production time in addition to replacement cost for each break down and specific energy norms going up. Average benefits gained by the plant due to reduction in breakdown: 1. Average monthly cost saving by INR 240, due to avoided maintenance cost 2. Average increase in production time - 98 hours per month Effect on Electricity Charges: Apart from reduction in breakdown, installation of harmonic filter also helped in reduction of specific energy consumption.table-6 shows reduction in average electricity cost on monthly basis. Months Energy Consumption kwh Maximum demand kva ACTUAL ELECTRICITY BILL Monthly Average - FY13 Monthly Avg Jun-Oct13 1,891, ,778, , , % Change by 6% by 14.77% APQI (C) Copyright (2013) All Rights Reserved 14

15 Unit rate - INR per kwh Demand Charges INR per kva Part "A" Energy Consumption Part "B" Maximum Demand Total (A+B) Surcharge For 110% of Contact Demand Miscellaneous Charges (Voltage Rebate) Current D.P.S After Date D.P.S Total (C) Total (A+B+C) Rebate (PF/LF/Voltage):2% of Total (A+B) Total Assessment in Rs Total Assessment in Rslakhs ,216, ,603, ,170, ,849, ,957, ,453, , , , , , , (80,038.24) (157,088.62) 11,877, ,295, , , ,638, ,066, by 6% by 14.77% by 4.22% by 100% by 4.22% by 100% by 143% by 96% by 4.9% by 4.22% by 4.9% by 4.9% Table-6 Energy cost Before and after harmonic filter While assessing change in energy consumption, production levels were also considered. Average monthly production for the financial year was 10,935 tons. Average monthly production recorded for the period of June to October 2013 was 11,632 tons. There is increase in production by 6.4% and reduction in energy consumption by 6%. Overall reduction in monthly average electricity bill was 4.9%. With the reduction in energy consumption and increase in production, specific energy consumption of the wire rod production has reduced significantly. SPECIFIC ENERGY CONSUMPTION Parameter Monthly Monthly % Change APQI (C) Copyright (2013) All Rights Reserved 15

16 Average - Avg Jun- FY13 Oct13 Finish Machine Production in tons by 6.4% KWH/Ton of Production (JSEB) by 11.6% Rs/Ton of Production by 10.6% Table-6 Specific Energy Consumption From the table-6 it can be seen that after installation of passive harmonic filter, finished machine production has increased by 6.4%. One of the factors of increased productivity can be attributed to reduced breakdowns. Apart from increase in production, there is reduction in energy consumption. Reduction in energy consumption is due to reduction in losses arising out of harmonic current. With increase in productivity and reduction in energy cost, specific energy consumption is reduced by 11.6%. The benefits gained by the plant can be summarised as: 1. Reduction in maintenance, repair and replacement cost due to breakdowns. 2. Increased production due to reduction in breakdowns 3. Reduction in specific energy consumption Financial Analysis: Financial benefits gained by the plant after installation of harmonic filter can be classified under two heads. 1. Reduction in specific energy consumption 2. Reduction in maintenance, repair and replacement cost of failed components Table-7 below shows financial analysis of the investment and benefits. Financial Analysis Part A - Reduction in specific energy consumption Unit of Measurement Rs/Ton of Production in FY13 1, INR/Ton Rs/Ton of Production on INR/Ton Net Gain in Rs/Ton of Production INR/Ton If Avg Monthly Production remains 11, Tons APQI (C) Copyright (2013) All Rights Reserved 16

17 Avg Monthly Monitory Gain INR 1,242, Average annual monitory gain - A INR 14,906, Part B - Reduction in maintenance, repair and replacement Average monthly reduction in maintenance cost 240, INR/Month Annual reduction in maintenance cost - B 2,880, INR/Year Total (A+B) 17,786, INR/year Investment 9,800, INR Simple Payback 7 Months Table-7 Financial Analysis From the table-7 it can be seen that the investment made by the plant to mitigate harmonics has paid back within 7 months. Conclusion: Reduction of production cost is one of the prime concerns of any production facility. In order to reduce operation cost, better control over manufacturing process and quality use of variable frequency drive is becoming common practice in the industry. Apart from utilisation of drives, PLC s are also integral part of any manufacturing process. As drives convert frequency, generation of harmonics cannot be avoided. Harmonics in the plant can cause: 1. Failure of various electrical/ electronic component 2. Increased energy losses due to heat generated by harmonics From the above case study, it can be seen that by reduction of harmonics a plant can be benefited in more than one way. The investment carried out to install harmonic filter can be paid back within a year. Benefits gained by the plant would be: 1. Significant reduction in specific energy consumption monetary benefit due to reduction in energy cost 2. Improved productivity due to reduced down time 3. Reduction in failure rate of various electrical/ electronic component Cost benefit for replacement/repair/maintenance of failed component APQI (C) Copyright (2013) All Rights Reserved 17

18 About the Author: Name: Jeetendra Kumar Jain General Manager- Usha Martin Limited, Wire & Wire Rope Division Mr. Jeetendra Kumar Jain is graduate mechanical engineer and MBA in operations. He is currently heading engineering activities at Usha Martin. Apart from Engineering & Projects, he is also looking after Safety, Environment, Risk Management, Branding, Kaizen Cell and IMS. Mr. Jain has successfully reduced operating cost by reducing energy cost, operating practices and process improvements in his past assignment at Hindalco and AMCO. At Usha Martin he initiated various energy conservation projects that also include reduction in harmonics. Disclaimer: The sole responsibility for the content of this document lies with the authors. It does not represent the opinion of the Asia Power Quality Initiative and /or ICPCI/ICA network. APQI and ICA network are not responsible for any use that may be made of the information contained therein. APQI (C) Copyright (2013) All Rights Reserved 18