Time Delay Technique for Pinpointing PD Noise on Combined Cycle Systems Troy Coleman, Plant Technical Services

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Scott Copeland
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1 Time Delay Technique for Pinpointing PD Noise on Combined Cycle s Troy Coleman, Plant Technical Services

2 Puget Sound Energy >1 Million Customers 772 MW Wind 3 Farms 276 MW Hydro 2 Projects 2481 MW Thermal 11 Sites 3529 MW Total 21.9% 7.8% 70.3% 2

3 Generator Stator Partial Discharge Record data every 6 months TGA-BP Pulse Qm (Magnitude) and NQN (Quantity) Check for changes in PD over time Doubling of PD in 6 months Severe Sumas Gas Turbine Generator 3

4 Goldendale, 1:1 Combined Cycle GE 7FA Gas Turbine 168 MW 18 kv Siemens Steam Turbine 84 MW 13.8 kv 4

5 High PD ( mv) Date Analyzing Stator (A PD phase) Difficult (A phase) Needed to use a 10:1 Attenuator to capture PD. 5

6 Hunting the elusive PD signal High PD throughout plant 230 kv 13.8 kv 18 kv 5 kv Switchgear 480 Switchgear 84 MW 168 MW Steam Turbine Generator Gas Turbine Generator 6

7 Need distance between both couplers 5ft Between 10ft 200ft Coupler Coupler 7

8 Adding Additional Coupler 10 feet apart Generator Generator Circuit Breaker Partial Discharge 80 pf Coupler 49 feet apart *New A B C Generator Step-Up Transformer 8

9 New distance between couplers Between 5ft 60ft 150ft Coupler Coupler New* Coupler 9

10 PD Coupler Coupler Equal Lengths Coax Cable A B C Coupler receives pulse after the Coupler = + Between Length ref 10

11 PD Coupler Coupler Equal Lengths Coax Cable A B C Coupler receives pulse before the Coupler = - Between Length ref 11

12 Between PD Coupler Coupler Equal Lengths Coax Cable A B C ref Pulse will arrive at one of the couplers before the other at a time delay < Between Length < Between Length 12

13 PDView Between Plot Technique! Notice Scale Between Coupler Coupler Where is your PD? Pulse Time Compared to Pulse Time = + Between Length = - Between Length Between < Between Length 13

14 PDView Plots Source: Iris PDView 14

15 Changing Time Delay Setting Source: Iris PDView 15

16 Adjusting Time Delay Settings Time Delay Setting: 90 nano seconds (thinks bus is 90 feet) Between Activity 65 feet 100 nano seconds 65 feet 100 nano seconds A Activity B C ref Pulses will travel at.65 ft/ns in coax Pulses will travel at 1 ft/ns in bus Time difference is 60 ns. Therefore PD is Between 16

17 Adjusting Time Delay Settings Time Delay Setting: 70 nano seconds (thinks bus is 70 feet) Between Activity 65 feet 100 nano seconds 65 feet 100 nano seconds Receives pulse at 175 ns A B C Receives pulse at 115 ns Activity ref Difference is 60 ns. Therefore PD is Between 17

18 Adjusting Time Delay Settings Time Delay Setting: 50 nano seconds (thinks bus is 50 feet) Between Activity 65 feet 100 nano seconds 65 feet 100 nano seconds Receives pulse at 175 ns A B C Receives pulse at 115 ns Activity ref Difference is 60 ns. Therefore PD is 18

19 Adding Additional Coupler 15 kv Coupler Actuator SF6 Breaker Disconnect 19

20 Adding Additional Coupler 20

21 Creating Equal Lengths Existing couplers had 24 coax cables. Our new* system coupler had a 88 coax cable. To create equal lengths, we needed a temporary 64 coax cable. Generator Generator Circuit Breaker 24' cable 24' cable *New A 64' cable B C ref 88' cable Generator Step-Up Transformer Off by 48.6 ns (Bus Length) 21

22 Changing Time Delays (59 feet apart) Time Delay Between 56 ns 55 ns 54 ns Shifted the Time Delay by 5ns. The noise is occurring a few feet from the coupler, which puts us in the circuit breaker 22

23 Source in Circuit Breaker? 23

24 SF 6 Gas Testing The gas tested normal: 99.9% Purity < 200 ppm dew 0 ppm SO PSI 24

25 Visual Inspection Aux Equipment Tested all the auxiliary equipment: Disconnect Bushing Surge Arrester Capacitor Voltage Transformer 25

26 Visual Inspection Inside Breaker CB DS 26

27 Source of Partial Discharge? MegOhm Tester: 1.65 MΩ 13.8 kv Actuator Grease Ground 27

28 Next Steps 1. Contacted manufacturer 2. Consulted other engineers 3. Cleaned actuator grease off 4. Put unit back in service 5. Re-perform PD testing 6. Re-inspect on next outage 28

29 Mint Farm, 1:1 Combined Cycle GE 7FA Gas Turbine 174 MW 18 kv Fuji Electric Steam Turbine 86 MW 13.8 kv 29

30 Hunting for Discharge Date (C phase) Between (C phase) (C phase) June 1 st 2015 (rain) June 9 th 2015 (dry) No or Between PD, so we decided to add an additional coupler further down the bus to increase our Between distance. 30

31 Adding Coupler Generator 24 feet apart Generator Circuit Breaker Partial Discharge 80 pf Coupler 150 feet apart Coax: 89 feet *New 89 feet A B C ref Generator Step-Up Transformer 31

32 Next Steps 1. Wait for the end of the outage when the unit is back in service. 2. Perform PD testing at earliest convenience, on a dry day. 3. Adjust time delay settings until the Between signal switches to a signal. 32

33 Thank you! Questions? 33

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