How To Ground Electronic Equipment In Southern Company? Imagination at work

Transcription

1 How To Ground Electronic Equipment In Southern Company? Imagination at work

2 Surge Protection of Capacitor Feeder Controllers Robert Cheney Alabama Power John Skliutas GE Digital Energy Don Guinn Progress Energy Dr. Suresh Gautam GE Digital Energy

3 Surge Protection of Capacitor Feeder Controllers How to Ground a System when the Flash Density goes from 9-12 Flashes/Square Mile/Year to Flashes/Square Mile/Year?

4 Southern Company Distribution Automation Distribution Reclosers and Motor Operated Switches 6368 Distribution Switched Caps 1494 Distribution Line Regulators 553 Faulted Circuit Indicators 285

5 Southern Company Distribution Automation Every year since % of APCO s controls are destroyed by atmospheric events. 5 7% of our Line Reclosers Have Experienced Flashed Bushings. 5 7% of our MOD Switches Have Flashed Insulators. At One Time Switched Cap Banks had a Mortality Rate of 10%.

6 Well How Do We Ground and Where Should We Put Arresters On this Standardized Specification

7 SOCO Company South West East APCO Grounding Conductor #6 #6 #4 #2/0 Arrester on Cap Bank Y Y Y Y Arrester in the Control N N Y Y Arrester on 1 kva Trans. N N N N Install 1 kva Trans. on Pole Line Device N???? Y Ground Rods 1 Many?? 3 Rods in Pole Hole Y?? Y N So Who Is Right or Is There A Right?

8 2013 Proposed a project to DSTAR to Determine How to Ground and Where to Place Arrester for Switched Capacitor Installations. Results will be Shared, Distributed and used for Design of Future Standardized Specifications.

9 DSTAR Project 14-4 Methodology Survey DSTAR membership. Select feeder capacitor pole configurations for simulation. Develop ATP model of equipment. Perform parametric study. Identify best practices.

10 What is the Issue? EMC Propagation of unwanted EM Energy Source Inductive & Capacitive Coupling Conductive Victim Radiative Several modes of propagation!

11 Lightning Impact on Controllers Fundamentals Approximate Primary Circuit Reduced Primary Circuit A Complex Voltage Divider!

12 Lightning Impact on Controllers Fundamentals Pole top 25 [ka] 20 Down lead current (Full model) [us] 50 (f ile Southern.pl4; x-v ar t) c:sys_n -XX ~25/2 ka/µs * 13.5 µh +36 kv + 10 ka*10/3 Ω = ~238 kv 25 ka * 10/3 Ω = ~83 kv [kv] 200 Critical parameters: Peak I L di/dt Pole resistance Arrester P.L [us] 50 (f ile Southern.pl4; x-v ar t) v :PH_C Pole top potential (Full model)

13 Lightning Impact on Controllers Fundamentals 250 [kv] 200 Controller H1 H2 H1 H [us] 50 (f ile Southern.pl4; x-v ar t) v :H1 v :H2 60 [kv] 50 H1 and H2 voltages to ground [us] 50 (f ile Southern.pl4; x-v ar t) v :H1-v :H2 H1 to H2 voltage. CPT is the link from system to controller. How to model CPT for impulse conditions?

14 Transient Performance of CPT Frequency Dep. Role of Transformer Stray Capacitances C 12 V 2 = C 12 C 12 + C 2 V 1 V 2 = Gain V 1 V 1 C 1 P S C 2 V 2 C 12 C 12 + C 2 = Gain For impulses: V 2 = C 12 C 12 + C 2 V 1 If C 12 = 150 pf, C 2 = 100 pf, then Gain Impulse = 0.6 For 60 Hz: V 2 = V 1 = Gain V 1 Gain 60 Hz = 1 60 = Gain Impulse Gain 60 Hz = 36

15 Transient Performance of CPT Capacitive coupling is dominant during lightning (a fast transient event). Accurate modeling of stray capacitances is very important. Winding capacitance not generally known. CPT Test set up Nameplate information

16 Transient Performance of CPT ATP Model and CPT Test Comparison Frequency scan from primary with secondary shorted. (x denotes data point from ATP model) Frequency scan from secondary with primary open. (x denotes data point from ATP model)

17 Terminal Model of CPT CPT model with floating secondary winding. Benchmarked with impulse tests.

18 Surge Protection of Controllers 250 [V] (f ile CPT_X1_X2_f loating_impulse_testing_(test_3).pl4; x-v ar t) v :XX0002-XX0003 factors: offsets: X2 to X1 voltage: +45 V to -110 V kv, 1.2*50 µs impulse. ~600 khz. X2 to X1 voltage: +43 V to -92V kv, 1.2*50 µs impulse. ~538 khz. (Applied impulse voltage reduced by factor of 10 with 100 V offset). +45 V to -110 V 600 khz +43 V to -92 V 538 khz

19 Simulation Setup Parametric study (4 grounds by 5 arrester matrix) Lightning surge Dashed lines represent variation in connection Red: Surge Arrester Green: Ground Loop Purple: Capacitor Ground

20 Arrester matrix Simulations Simulation Matrix Grounding matrix A [1010] B [1110] C [1100] D [1000] E (EPRI Recommended) 1 (No Arrester) 2 (Arrester at CPT Secondary Only) 3 (Arrester at controller) 4 (Arrester at CPT Secondary and Controller) 5 (Arrester at CPT Primary Only) A1: XXXX B1 C1 D1 A2 B2 C2 D2 A3: XXXX B3 C3 D3 A4 B4 C4: SoCo D4 A5 B5 C5: SoCo D5 Controller neutral connected to ground via arrester. No ground connection at transformer secondary. No ground connection of secondary neutral in the capacitor junction box at the pole top. Circled cases: 1) CPT secondary voltages < 0.83*10 kv BIL 2) Controller voltage < 2.5 kv

21 Simulations A1 (XXX Energy) Controller neutral and transformer primary neutral connected to ground lead No arrester Blue: Voltage Across Transformer Primary Terminal Red: Voltage Across Transformer Secondary Terminal Green: Voltage Across Controller Terminal

22 Simulations C5 (SoCo) CPT primary neutral and secondary neutral connected to down lead and controller neutral floating and connected to CPT neutral Arrester at transformer (CPT) primary only Blue: Voltage Across Transformer Primary Terminal Red: Voltage Across Transformer Secondary Terminal Green: Voltage Across Controller Terminal

23 Summary Surge Protection of Controllers (DSTAR P14-4) indicates: - No common utility controller installation practices. - Control circuits and equipment grounding not de-coupled. - Arresters can override bad grounding practices. - CPT primary protection not optimized with cap bank arresters. - 3 rd best: CPT secondary and controller arrester. Next Step: - Perform full scale impulse testing. New DSTAR Project Spot check P14-4 results. DSTAR: - Conducts practical research. - New members welcome.

24 Project 15-7 Impulse Testing of Controllers 2.1 MV GE impulse generator Alabama Power Outdoor Test Area

25 What is DSTAR? DISTRIBUTION SYSTEMS TESTING, APPLICATION, AND RESEARCH DSTAR is a consortium of utilities organized to cooperatively sponsor practical and cutting edge distribution systems research and development.

26 DSTAR : Active Member Utilities: P14 and P15 Ameren APPA/DEED Duke Energy* NRECA/CRN PacifiCorp Progress Energy* South Carolina E&G Southern Company * Merged

27 Questions? Thank you!