2016 Del Rio Hail Storm

Bret Burford, PE & Michael Skidmore, PEAEP Transmission

Corpus Christi, TX & New Albany, OH

Texas A&M Relay ConferenceCollege Station, TX

March 27-29, 2018

2016 Del Rio Hail Storm

• Storm Highlights

• System Configuration Prior to the Storm

• Sequence of Outages during the Storm

• Equipment Failures

• Equipment Failure - Mitigation

• Protection System Misoperation

Storm Highlights

• Storm started at 22:14 CST on 2/22/2016

• Golf ball size hail in Del Rio and Winds up to 70 mph

• Drivers coming from Uvalde on Hwy 90 reported Baseball

size hail

• All of Del Rio lost power at one point

• AEP/ETT Hamilton Road 138kV substation suffered damage

• All power was restored in approximately 14 hours

Storm Highlights – Customers Out

System Configuration Prior to the Storm

9110

to

Escondido to SVC1 to SVC2

2210

9345 1165

9255

Picachoto Amistad

Hydro

Buena

Vista

Del Rio

to Sonora

7335

3705

7285

9465

1520

#2 Bus

#1 Bus

115

125

1170

1220

to Illinois 4

(construction)

Comstock

Rough

Canyon

Hamilton Roadto Odlaw

Legend:

RED – In Service

GREEN – Open

PST

Sequence of Outages during the Storm

9110

to

Escondido to SVC1 to SVC2

2210

9345 1165

9255

Picachoto Amistad

Hydro

Buena

Vista

Del Rio

to Sonora

7335

3705

7285

9465

1520

#2 Bus

#1 Bus

115

125

1170

1220

to Illinois 4

(construction)

Comstock

Rough

Canyon

Hamilton Roadto Odlaw

Legend:

RED – In Service

GREEN – Open

BLACK – Low SF6 Lockout (closed)

PST

@ 22:14

@ 22:19

@ 22:25

Four 138kV CBs experience low SF6 and stay closed due to low

SF6 lockout in the span of 2.5 minutes (22:27:24 to 22:29:49

CST).

Sequence of Outages during the Storm(2)

9110

to

Escondido to SVC1 to SVC2

2210

9345 1165

9255

Picachoto Amistad

Hydro

Buena

Vista

Del Rio

to Sonora

7335

3705

7285

9465

1520

#2 Bus

#1 Bus

115

125

1170

1220

to Illinois 4

(construction)

Comstock

Rough

Canyon

Hamilton Roadto Odlaw

Legend:

RED – In Service

GREEN – Open

BLACK – Low SF6 Lockout (closed)

PST

22:31:12.849 - LG fault on Del Rio line (no pilot scheme)

25 cycles – 1165 opens, 9255 fails to trip due to LO condition

37 cycles - 9255 BF trips #2 Bus CBs except 9465 which is in LO condition

65.5 cycles – fault evolves to LLG fault

73 cycles – Bus 2 bus differential relay trips

88 cycles – 1520 opens due to 9465 BF trip and DTT sent to Odlaw end

90 cycles – Odlaw CBs trip to clear the fault

@ 22:31

Sequence of Outages during the Storm(3)

9110

to

Escondido to SVC1 to SVC2

2210

9345 1165

9255

Picachoto Amistad

Hydro

Buena

Vista

Del Rio

to Sonora

7335

3705

7285

9465

1520

#2 Bus

#1 Bus

115

125

1170

1220

to Illinois 4

(construction)

Comstock

Rough

Canyon

Hamilton Roadto Odlaw

Legend:

RED – In Service

GREEN – Open

BLACK – Low SF6 Lockout (closed)

PST

00:18:02.357 – 9110 faults internally (LG) and fails to trip due to LO condition

#1 Bus CBs trip by Bus differential relay

Escondido end trips

Now all of Del Rio is in the dark!

@ 00:18

Sequence of Outages during the Storm (4)

Last Try:

• Closed 3705 by SCADA in attempt to

get 138kV bus #1 energized, but it

tripped back out.

• Sonora Line relays (D60/SEL421)

tripped by PH Z1 element, however

Sonora end did not trip.

• See “Misoperation” slide later in this

presentation for details of what

really happened here.

• This should not have been

attempted without isolating CB 7285

and CB 9110 on Bus #1.

• Now waiting on personnel to get to

Hamilton Road station after the hail

storm abates.

to Sonora

72853705

7335

PST

Equipment Failures

Four 138kV SF6 circuit breakers lost SF6 pressure and went to

low pressure lockout condition in a 2.5 minute span.

Equipment Failures

• Hail damaged the rupture disks and allowed SF6 to vent.

Equipment Failure - Mitigation

https://www.youtube.com/watch?v=ITVp7gCNp4E

• 138kV Phase Shifting Transformer was 1 step off-

neutral when 3705 was closed; shorting an

energized coil. (NOT GOOD)

• PST Tap position indication was not working at

the time and was waiting on parts to fix.

• Created 14 kA of circulating current though the

PST and only appears as 500 A at the Sonora

end.

• PH Z1 elements tripped on Line zone (5 cycles)

and beat the Circulating current detection that

trips 7285. (MISOP) (GOOD)

• 7285 was in Closed LO condition and would have

required BF to trip in 10-15 cycles to clear the

condition.

• Why did the Line zone PH Z1 element trip?

to Sonora

72853705

7335

PST

Protection System Misoperation

14 kA

Protection System Misoperation

Line zone relays show

current spikes that cause

PH Z1 elements to trip.

There are two CB CT

sources in parallel to form

the ring terminal line zone,

CBs 3705 and 7285.

Protection System Misoperation

CB 3705 BF relay currents

look OK.

CB 7285 currents look slightly

distorted in BC phases below.

Thus, the Line zone PH Z1 elements tripped due to unequal CT saturation of the

two CT sources causing a non-zero value output in error.

Thank You

Questions?