Fault Locating at Pacific Gas and Electric Company

Transcription

1 Fault Locating at Pacific Gas and Electric Company i-pcgrid 2015 Scott Hayes

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4 Relay Targets were the earliest fault location devices.

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6 Light Beam Oscillographs and later Digital Fault Recorders

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8 Microprocessor Relays Microprocessor based protective relays were an off shoot of digital fault locator research. Since 1990 PG&E has actively used MP relays to provide fault locations. Improved customer reliability. Reduced patrol costs. 50 mile line. Foot patrol or $1000 per hour helicopter?

9 Fault Location Algorithms Takagi Method Improved Takagi Method Enhanced Improved Takagi Method Variation of Ohms Law. R = V/I

10 Typical relay calculated fault display Event: AG T Location: Frequency: 60.0 Targets: INST ZONE1 EN G 50 V1 Mem: / 58 Early efforts relied on dial up modems, sharing existing phone lines or in some cases installing terminal printers in substations for line personnel to access relay calculated fault locations.

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12 Relay Calculated Fault Locations All modern relays can calculate fault locations and output the information to SCADA. Why would engineers need to get involved? Can fault locations be successfully done on distribution circuits?

13 Factors Affecting Fault Location Accuracy 1. 3 phase faults are relatively accurate on two terminal lines. 2. Ground faults are the most inaccurate due to several factors. 3. Load current and fault current mixed together decreases accuracy. 4. Untransposed lines decrease accuracy. 5. Tapped lines decreases accuracy both for three terminal transmission lines or tapped load or generation stations. 6. PG&E standard transformer connections for distribution banks make fault locations less accurate for ground faults than at almost all other utilities. 7. Mixed conductor size on a circuit decreases accuracy. 8. Double circuiting decreases accuracy. 9. Paralleled conductor decreases accuracy. 10.Series cap banks decrease accuracy. 11.Wood pole construction decreases accuracy by increasing fault ground fault resistance.

14 PG&E System Topology PG&E 115 kv and 60/70 kv Transmission Lines often have taps, multiple wire sizes and multiple sources. Our standard distribution transformers (115/12 kv or 60/12 kv) are connected:

15 PG&E Transmission Circuit Miles /70 kv 115 kv 230 kv 500 kv

16 Average Circuit Outage Rate Series /70 kv 115 kv 230 kv 500 kv

17 Number of Fault Location Provided

18 Fault Type and Voltage Distribution 2014 Faults by Voltage 500 kv, 3.1% 230 kv, 10.1% 60 kv, 45.3% 115 kv, 34.0% 500 kv 230 kv 115 kv 70 kv, 7.5% 70 kv 60 kv

19 Travelling Waves Travelling wave fault location(twfl) shows the most promise for improved accuracy but is not widely applied. PG&E had a travelling wave fault locator in the 1970 s. Required a comm tech, variable frequency generator and amplifier. Applied on 230 kv s Created our own TWFL system using GOES clocks and voltage inputs. Applied on 500 kv s - Applied several commercial TWFL equipment using current inputs on EHV system TWFL is now integrated into some line relays.

20 Conclusions Fault Locations Improve Service Reliability and Decrease Patrol Costs. Due to PG&E Transmission Topology, Engineer Calculated Fault Locations are Preferred. PG&E System Protection is Committed to Providing Fault Locations 24/7/365. Challenge: Maintaining Reliable Remote Relay Access with Changing NERC CIP Requirements.