Mystery Solved: Five Surprises Discovered With Megahertz ...

© 2019 SEL and AEP

Mystery Solved: Five Surprises Discovered With Megahertz Sampling and Traveling-Wave Data Analysis

E. O. Schweitzer, III, V. Skendzic, A. Guzmán, M. V. Mynam, and J. L. Eternod

Schweitzer Engineering Laboratories, Inc.

Yanfeng GongAmerican Electric Power

• Detection of surges produced by lightning• LOCATION of lightning-induced surges• Breaker restriking and waves launched• HV transients• HV transients we located

MHz Sampling, 18-Bit Resolution, Absolute TimeMillisecond Protection, 100 ft Fault Locating, Greater Visibility

Clarke Components Work for Traveling WavesSymmetrical Components Don’t

α β 0

Can’t use symmetrical components because I1 and I2depend on the “a” operator…which only works with phasors

One Event Reveals Precursor Lightning Surges, BG Fault, and Breaker Restrike

Volta

ge (k

V)

0

100

200

–200

–100

Cur

rent

(A)

0

4000

–4000

8000

500–50 Time (ms)

Ib

Iα and I0 Components Dominate Ground Fault

0

8000

–4000

Cur

rent

(A)

0

–4000

8000

500–50 Time (ms)

Cur

rent

(A)

4000

4000Ib

IαI0

Differentiator-Smoother Accentuates Transientsand Attenuates System Frequency

t

di/dt

tat

i

i(t)is(t)

di/dt

Current Arrival Timei(t) is(t)

tadi/dt

d/dtSmoother

(LPF)Differentiator Time-of-

Peak Estimator

Interpolate to50 ns accuracy

0

500–50 Time (ms)

Cur

rent

(A)

Differentiator-Smoother Accentuates Transientsand Attenuates System Frequency

4000

–4000

0400

–400

0400

–400

Ib

Iα

I0

Rescaling I0 Reveals Prefault Transients18-bit resolution provides excellent dynamic range

500–50 Time (ms)

Cur

rent

(A)

Ib0

4000

–4000

0400

–400

0

20

–10–20

10

Iα

I0

Cur

rent

(A)

0

40

0

–40

–4

Similar Transients in All Three Phases: I0BPA Verifies Lightning Was Nearby

I0

80

–80

–8

–12

4

–36 –34Time (µs)–35

Cur

rent

(A)

0

400

0

–400

–400

800

–800

–800

400

Lightning Triggers BG Fault at T = 0Reflections From the Fault and Remote Terminal

0 Time (µs)100 200 300 400 500

Reflection from fault

Reflection from remote terminal

Iα

TW Fault Locator Reported Fault 65.5 km

From GoshenBPA Verified Location

0

Tim

e (µ

s)

200

400

600

800

1000

1200

1400

Cur

rent

(A)

0

100

0 Time (ms)

Breaker Restrike Delays Fault Clearing ½ CycleVo

ltage

(kV)

200

–100

–200

20 40 60

0

40002000

6000

–2000

Ib

40 45 50 55Time (ms)–4000

–2000

0

2000

4000

Cur

rent

(A)

47.2 47.4 47.6 47.8 48 48.2 48.4 48.6Time (ms)

–2000

–1500

–1000

–500

0

Breaker Restrike Delays Fault Clearing ½ Cycle

Restrike Reflectionfrom fault

Reflection from remote end

Restrike Launches WaveWhich Bounces Off Fault

and the Remote End Tim

e (μ

s)

–200

0

200

400

600

800

10000 50 100

Distance From Local Terminal (km)

RestrikeFault

Restrike reflected from fault

Restrike reflected from remote end

Location of Lightning-Induced Surges

MHz Records Track Lightning Storm as It Moves Across CFE 400 kV System

Over 30 records triggered in 35 minutes with NO faults

R

MID

IBD CHM

TMD

223.8 km

33.6 km195.2 km 102 km

20 km

5.6 km

144 km

R

102 km

144 km

Each Record Shows Multiple Transients Both on Voltages and Currents

Cur

rent

(A)

0200

0 Time (ms)

Volta

ge (k

V)

400

–200–400

0

200100

–200

50 100

–100

300

I0 Dominance Suggests Lightning CFE Verifies Lightning Was NearbyC

urre

nt (A

)

0

200

0 Time (µs)

–200

0

80

40

–80

–40

200 400 600

All Recorded Transients Share Common Shape

I0

No fault,so only reflection

is from remote end

Double-Ended Fault Locating Detects

Location of Lightning Activity

–500

0

500

1000

1500

2000

MID

0 100 200Distance From MID (km)

TMD

Tim

e (μ

s)

Transients Move Across System Like a Storm!

21:50 22:00 22:10 22:20 22:30Local Time (hh:mm)

90

95

100

105

110

115

120

125

Dis

tanc

e Fr

om M

ID (k

m)

High-Voltage Transients

Sudden Onset of Transients but No Faults

R

MID

IBD CHM

TMD

223.8 km

33.6 km195.2 km 102 km

20 km

5.6 km

144 km

R

102 km

144 km

Transients on Voltages and Currents Confirm System Disturbance, not Secondary Wiring

Cur

rent

(A)

0200

0 Time (ms)

Volta

ge (k

V)

400

–200–400

0

800

400

–800100 150

–400

50

• Wave propagates from MID toward TMD

• Source is behind MID• Most likely at MID bus

Transients Originate Outside the Line Zone

Tim

e (μ

s)

–200

0

200

400

600

800

1000

1200

1400

1600

MID

0 100 200Distance From MID (km)

TMD

Source of transient unknown Investigation in progress

AEP Engineers Concerned About 765 kV TransientsOscillogram shows first of three records, in 15 minutes;

Second one was similarC

urre

nt (A

)

0

0 Time (ms)

Volta

ge (k

V)

0

2000

600

–2000

200 400–200

–2000

2000

First and Second Events Triggered by Disconnect Closing; Third by Breaker Closing

Reactor Breaker

Disconnect

R

39.7 kmLine Trap

16.3 km 187.4 km

Station 1

Station 2 Station 3

Station 4

Cur

rent

(A)

0

0Time (ms)

200–200

2000

1000

–2000

–1000Closing disconnecttriggered a flurry of transients.Breaker closing produced clean transients.

Here’s the Third Record…When Reactor Breaker Closed

Cur

rent

(A)

0

0 Time (ms)

Volta

ge (k

V)

0

2000

–2000

10–10

–2000

2000

1000

–1000

20

Transients From Each Event Show the Same Reflections Suggest All Events Occurred at the

Same Location

Cur

rent

(A)

–0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6Time (ms)

–50

0

50

–50

0

50

Vol

tage

(kV

)

–0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6Time (ms)

Reflection From Station 2

Reflection From Station 3

First and Second Events Triggered by Disconnect Closing; Third by Breaker Closing

Reactor Breaker

Disconnect

R

39.7 kmLine Trap

16.3 km 187.4 km

Station 1

Station 2 Station 3

Station 4

Cur

rent

(A)

0

0Time (ms)

200–200

2000

1000

–2000

–1000Closing disconnecttriggered a flurry of transients.Breaker closing produced clean transients.

• Lightning surges produce I0 only … no Iα or Iβ• We can locate lightning surges• Restriking launches waves in α and 0 modes• We can locate faults from the restrike waves• We can locate origin of high-voltage transients• Modes help us differentiate between lightning, faults,

restrikes, and incipient faults

MHz Sampling Reveals Details We Seldom See