Locating Faults by the Traveling Waves They Launch

Transcription

1 Locating Faults by the Traveling Waves They Launch Edmund O. Schweitzer, III, Armando Guzmán, Venkat Mynam, Veselin Skendzic, and Bogdan Kasztenny Schweitzer Engineering Laboratories, Inc. Stephen Marx Bonneville Power Administration Copyright BPA and SEL 2014

2 Some Faults Are Easy to Find

3 Flashed Insulators Are Hard to Find

4 Accurately Locate Faults With Traveling Waves For a fault at miles Method Distance (miles) Difference (miles) Impedance Traveling wave (TW)

5 Estimate Location From Current JM Drop circa 1936 Adheres to Standard SIS 12 AWG/10-32/5A Quick Test, 2013 Set Measured Not bad for 77 years!!!

6 Estimate Location From Impedance V S m 1 m V R I S I F I R Line Impedance = Z L

7 Impedance-Based Methods Widely available in line relays today No communications required, but need voltages and currents Transients: faster relays and breakers Series compensation, mutual coupling, transposition CCVT accuracy and transient response

8 Faults Launch Traveling Waves L m l m R m 2m 2(l m) 3m

9 Currents and Bewley Lattice Diagram 0 Drummond B (A) BG Fault, June 04, 2013 km Goshen B (A) Microseconds

10 Two-End TWFL Method m L R t L t R BECKY 1 m t t v L R 2 l BECKY

11 Automatic Fault Locator (BPA, 1972) L R Wave L Wave R TW Processing Unit Start Counter Stop Microwave Receiver Master Terminal TW Processing Unit Microwave Transmitter Remote Terminal

12 Practical Considerations CTs are pretty hi-fi, bandwidth > 100 khz CCVTs are not, except at the capacitive voltage divider tap, but that means new cabling Use currents and two-end method Fit naturally in current differential relays Re-use same communications channel

13 Nature of Traveling Waves Lightning surges coupling onto line Wave launched by fault Reflections from discontinuities Messy electrical breakdown Can t expect textbook waveshapes

14 Clean Breakdown: CG Fault Current (A) Time (μs)

15 Precursory Waves: Shield Coupling?? Precursory Waves Main Flashover Wave 200 Current (A) Time (μs)

16 TW Fault Locator Design Concept Filter and sample currents Isolate desired mode Accurately measure time of arrival Exchange with other end, over same 87L channel Calculate location using two-end equation Save data

17 Simple Threshold Won t Work Current (A) Large Uncertainty (2 μs = 600 m) Time (μs)

18 Differentiator-Smoother Works Great Borrowed Idea From Leading Edge Tracking Current i(t) Smoother (LPF) i s (t) Differentiator d/dt di/dt Time-of- Peak Estimator Arrival Time t a i i(t) i s (t) di/dt Interpolate to 50 ns accuracy di/dt t t t a

19 Relative Accuracy ~ 50 ns R 1 t 1 Clock Dt = t 1 t 2 R 2 t 2 Mean Error = 17 ns or 8 Standard Deviation = 32 ns or 16

20 87L and TWFL Share 64 kb/s Channel 87L 87L and TWFL 64 kb/s network or point-to-point 87L Wide-Area Time Reference (Network or GPS) (for TWFL only)

21 BPA Experience 161 kv Line SEL-411L SEL DS1 Microwave Link SEL-411L SEL

22 Current Current Gunshot Phase Currents at Goshen and Drummond 200 Goshen Terminal Drummond Terminal

23 We Know Where Your Faults Are Nature of Fault Line Patrol (miles) TW (miles) Flashover Lead projectile Lightning Flashover Flashover Flashover Accuracy within one to two tower spans

24 BG Fault Located at 62/10 Irrigation Closest Tower

25 BPA Experience Tapped Lines Redmond Yew Ave. Tap Brasada Brothers Tap Hampton Tap Riley Tap Harney

26 Line Patrol It Was Like Chasing Ghosts on This Line Nature of Fault Line Patrol (miles) TW (miles) Flashover Flashover Flashover * Flashover Flashover * Bird waste Accuracy within one to two tower spans *Single-ended fault location

27 Line Patrol Found These Flashed Insulators

28 Summary of Typical Errors Relay Error 50 ns 25 Timing (clock) 50 ns 25 Line Length (0.1% of 100 mi) 500 Speed 0.05% 250 Allowance for other errors 250 on the order of one span

29 Traveling Wave Fault Locator Fits hand-in-glove into differential relay Easy to set up and use Not affected by series caps, mutual coupling, or very fast clearing Complements impedance methods Adds to our understanding of lines

30 TWFL on Cables In Service on 345 kv Underground Cables

31 Waves Propagate Slower in Underground Cables Wave Velocity = 0.48 Times Speed of Light