Don Sevcik
EEI Fall 2013 Transmission, Distribution & Metering
October 6-9, 2013
Charleston, SC

Company   Overview
• CenterPoint Energy is a gas and electric delivery company operating in several states.
• CenterPoint Energy Houston Electric (CEHE) is a structurally unbundled transmission and distribution utility serving Houston,
Galveston, Freeport, Baytown, and surrounding communities in the state of
Texas. CEHE does not own or operate power plants, nor does CEHE participate in competitive electric energy markets.
• CEHE has a small geographic footprint, but serves approximately 25% of the electric load in the ERCOT region.
2

‘Street   Network’   and   ‘Spot   Network’
CenterPoint Energy offers a range of overhead and underground single phase, two phase and three phase types of services.
At CenterPoint Energy’s option, in certain locations, CenterPoint Energy offers service from 208V underground secondary ‘Street Network’ and 480V & 4160V secondary
‘Spot Networks’.
These secondary networks are characterized by a bus fed by multiple network transformers with a given secondary network operating voltage (208 V, 480 V, 4160 V).
Each network transformer has a 12.47 kV delta connected primary voltage winding.
For a given secondary network, each network transformer is connected to a separate
12.47 kV substation feeder.
All of the 12.47 kV feeders that supply a set of network transformers originate from the same substation.
Two substation power transformers supply all of the network feeders that make up a
‘network grid’.
3

Substation
‘Street   Network’   and   ‘Spot   Network’
Distribution   Substation   Bus
Feeder
Breaker
MUG   Network   Vault
Network   Xfmr
Δ /Y
Network
Protector
Secondary
Network   Bus
Local
Customer   Loads
N.C.
• Two   substation   transformers   are   connected   to   a   common   bus.
(Networked   Substation   Bus)
• Networked   underground   feeders   leave   the   sub   to   serve   MUG   network   vaults.
• Each   feeder   serves   a   MUG   network   transformer.
• The   network   transformer   secondaries are   connected,   through   a   network   protector,   to   a   common   bus.
• The   secondary   network   is   a   bus   fed   by   multiple   transformers,   from   multiple   locations,   at   a   given   operating   network   voltage   (208   V,
480   V,   4160   V).
• CNP   has   1 ‐ 208V   secondary   network   and   numerous   480V/4160V   spot   networks.
To   208V   Street
Network   Grid
• CNP   Network   Systems   are   designed   to   be   able   to   lose   a   circuit   without   effecting   the   customer
(N ‐ 1).
4

69 KV LINE 138-69 KV
AUTOTRANSFORMER
69 KV LINE
INDOOR SWITCHGEAR
12.47 KV UG NETWORK FEEDERS
12.47 KV UG NETWORK FEEDERS
12.47 KV UG NETWORK FEEDERS
12.47 KV OH FEEDERS
12.47 KV OH FEEDERS
12.47 KV UG NON-NETWORK FDRS
12.47 KV UG NETWORK FEEDERS
12.47 KV UG NETWORK FEEDERS
12.47 KV UG NETWORK FEEDERS
12.47 KV UG NETWORK FEEDERS
12.47 KV UG NETWORK FEEDERS
CABLE RISERS
POWER BUILDING
69-12.47 KV
TRANSFORMERS
69 & 12.47 KV
PROTECTIVE RELAYS
AND CONTROL
SUBSTATION
CONFIGURATION
5

POWER   BUILDING
I
I
OPEN TRANSFORMER
BUSES
ENCLOSED
I
I
SWITCHGEAR
SWITCHGEAR
FEEDER
CABLES
FEEDER
CABLES

October   5,   2006
TRANSMISSION
LINE AUTOTRANSFORMER
TRANSMISSION
LINE
TRF   2
A1
A4
A7
A10
A13
A16
TRIP
B2
B5
B8
B11
B14
B17
TRIP
A3
A6
A9
A12
A15
A18
TRF   5
Y
Y
Y
Y
INITIAL
1 ‐ PHASE
FAULT
7

October   5,   2006
TRANSMISSION
LINE AUTOTRANSFORMER
TRANSMISSION
LINE
TRF   2
A1
A4
A7
A10
A13
A16
TRIP
B2
SUBSEQUENT
MULTI ‐ PHASE
FAULT
B5
B8
B11
B14
B17
A6
TRIP
A9
TRIP
A12
TRIP
A15
TRIP
A18
TRIP
TRF   5
TRIP
Y
Y
Y
Y
8

October   5,   2006
SUBSTATION   69   KV
DIGITAL   FAULT
RECORDER
T   =   0
B2   opens   but   A3   interrupter   fails
Results   in   multi ‐ phase   fault
977   A   rms 2850   A   rms
Trf#5   69   kV   bkr   open
1900   A   rms
All   Trf#5   “A”   bkrs   open
1110   A   rms
983   A   rms 2860   A   rms
960   A   rms 2990   A   rms
1900   A   rms
1860   A   rms
1110   A   rms
1090   A   rms
9 9

Trf#2   69   Kv   bkr   open
1670   A   rms
October   5,   2006
1080   A   rms
1340   A   rms
1860   A   rms
1080   A   rms
1060   A   rms
SUBSTATION   69   KV
DIGITAL   FAULT
RECORDER
T   =   5   min.
10

SWITCHGEAR   CIRCUIT   BREAKER   COMPARTMENT
11

REMAINS   OF   SWITCHGEAR   CIRCUIT   BREAKER
12

SWITCHGEAR   ‘A ‐ B ‐ A’   CIRCUIT   BREAKER   COMPARTMENTS
AND   CABLE   RISERS   TO   INDOOR   OVERHEAD   BUS
13

INDOOR   OVERHEAD   12.47
KV   BUS
14

RESTORATION
• OTHER   TRANSFORMERS   WERE   MANUALLY   TRIPPED   TO   ALLOW   FIRE   DEPARTMENT   TO
PUT   OUT   THE   FIRE   IN   THE   CUBICLE.
• TOOK   8   HOURS   TO   ISOLATE   DAMAGED   EQUIPMENT,   CLEAN,   TEST   AND   RE ‐ ENERGIZE
FEEDERS   THAT   WERE   NOT   DAMAGED.
• REMAINING   CLEANUP   EFFORTS   TOOK   7 ‐ 10   DAYS   TO   COMPLETE.
• DAMAGED   SWITCHGEAR   AND   CIRCUIT   BREAKERS   WOULD   HAVE   TO   BE   REPLACED
LATER.
15

NEAR   TERM   FIXES
• SEND   similar   SWITCHGEAR   CIRCUIT   BREAKERS   FROM   FOUR   SUBSTATIONS   TO
MANUFACTURER   FOR   REHAB  ‐ ADD   STRUT   UPGRADE   KIT,   REPLACE   PUSH   RODS,
REPLACE   PRIMARY   TRIP   PROP   ASSEMBLY,   REPLACE   TRIP   SPRINGS,   REPLACE   CONTACT
SPRINGS,   ROUTINE   MAINTAINCE   LUBRICATION,   TESTS   AND   CHECKS.
• REPLACE   INDOOR   ENCLOSED   TRANSFORMER   BUS   WITH   OPEN   AIR   BUS.
• ADD   FIRE ‐ PROOF   BARRIER   TO   INDOOR   CONTROL   CABLE   TRAY.
• DEVELOP   AND   IMPLEMENT   A   NEW   SUBSTATION   BASED   ‘BACK   FEED’   PROTECTIVE
RELAYING   SCHEME.
16

TYPICAL   PROTECTION   SCHEME
69 kV
TR2
A1
50
BF
B2
TR5
A3
50
BF
C-T-S
50/
51
R-T-S
W/V
12 kV NETWORK
17

SUBSTATION   BASED   ‘BACK ‐ FEED’   PROTECTION
SCHEME
69 kV
TR2
A1
50
BF
B2
3 Split-
X F2
Core
1200/5
C150
A3
TR5
F3 X
50
BF
F4 X F1 X
12 kV NETWORK
C-T-S
50/
51
R-T-S
W/V
“BACK-FEED”
Protection
Scheme
“TRIP1” wire for BF schemes which utilizes “50” relays OR “TRIP1B” wire for BF schemes which utilize uP relays.
“BACK-FEED” MICROPROCESSOR RELAY
Either input starts & seals-in internal timer.
Timer set for BF clearing time + margin ( 30 to
60 cycles ). If 50 element is picked-up after timer delay then:
Trip
Both
Trf.’s
Alarm
SCADA
18

POWER   BUILDING
OPEN TRANSFORMER
BUSES
OPEN
I
I
SWITCHGEAR
SWITCHGEAR
FEEDER
CABLES
Install   Split ‐ Core   Feeder   CT’s   &
“Back   Feed”   Microprocessor
Relays
FEEDER
CABLES
I
I
19

‘BACK   FEED’   PROTECTION   – SPLIT ‐ CORE   FEEDER   CT’S
20

‘BACK ‐ FEED’   PROTECTION   – NORMAL   CONDITIONS
TRF   2
BUS
“Back ‐ Feed   trip”   scheme
Normal   conditions  ‐ No   trip   applied   to   any   breaker   or   to   the   microprocessor   relay
1200:5 300A 300A
A1 B2 A3
1200:5
1.25A
50/
BF
600A
1.25A
50/
BF
1.25A
1.25A
50/
51
2.5A
1.25A
2.5A
TRF   5
BUS
1200:5 uP
SUBSTATION
2.5A
1.25A
1.25A
NETWORK   FEEDERS
600A
21

TRF   2
BUS
A1
“F1”   FAULT   ‐ – NO   TRIP   FROM   ‘BACK   FEED’
MICROPROCESSOR   RELAY
0A Tripped   by feeder   protection
B2
50/
BF
0A
0A
SUBSTATION
NETWORK   FEEDERS
F1
X
0A
Tripped   by feeder   protection
A3
0A
TRF   5
BUS
0A
0A
0A
50/
BF
0A
50/
51 uP uP   relay timer   starts when   50/51   relay   operates
22

“F2”   FAULT   ‐ TRIP   FROM   ‘BACKFEED’   MICROPROCESSOR
RELAY   REQUIRED   AFTER   SET   TIME   DELAY
Tripped   by   ‘back ‐ feed’   protection
TRF   2
BUS
A1
0A Tripped   by feeder   protection
B2
F2
X
Tripped   by feeder   protection
A3
0A
Tripped   by   ‘back ‐ feed’   protection
TRF   5
BUS
50/
BF
0A
2400A   Max.
240A   Min.
SUBSTATION
10A   Max.
1A   Min.
0A
50/
BF
0A
0A
50/
51
10A   Max.
1A   Min.
uP uP   relay timer   starts when   50/51   relay   operates
23
NETWORK   FEEDERS

“F3”   FAULT   AND   A3   BREAKER   FAILURE   – TRIP   FROM
‘BACKFEED’   MICROPROCESSOR   RELAY   REQUIRED
AFTER   SET   TIME   DELAY
Tripped   by   ‘back ‐ feed’   protection
TRF   2
BUS
0A
A1
Tripped by   BF
B2
50/
BF
0A
2400A   Max.
240A   Min.
10A   Max.
1A   Min.
2400A   Max.
240A   Min.
Tripped   by bus   protection
TRF   5
BUS
F3 X
10A   Max.
1A   Min.
0A
10A   Max.
1A   Min.
50/
BF uP
10A   Max.
1A   Min.
50/
51 uP   relay timer   starts when   BF   scheme operates
SUBSTATION
24
NETWORK   FEEDERS

“F4”   FAULT   AND   B2   BREAKER   FAILURE   – NO   TRIP
FROM   ‘BACK   FEED’   MICROPROCESSOR   RELAY
TRF   2
BUS
Tripped   by feeder   protection
A1
2400A   Max.
240A   Min.
50/
BF
10A   Max.
1A   Min.
Tripped by   BF
A3
0A
TRF   5
BUS
10A   Max.
1A   Min.
0A
10A   Max.
1A   Min.
0A
50/
BF
10A   Max.
1A   Min.
50/
51 uP uP   relay timer   starts when   BF   operates
F4 X
2400A   Max.
240A   Min.
SUBSTATION
NETWORK   FEEDERS
25

December   27,   2012
A FAULT OCCURRED IN THE12 KV CIRCUIT BREAKER A3 COMPARTMENT.
THE NORMAL FEEDER AND TRANSFORMER PROTECTIVE RELAYS TRIPPED
TRANSFORMER #5 AND 12 KV CIRCUIT BREAKER B2 IN SIX CYCLES BUT THE FAULT
IN A3 CONTINUED TO BE BACK FEED FROM THE FEEDER VIA TRANSFORMER #2
AND THE DISTRIBUTION NETWORK.
THE SPECIAL ‘BACK FEED’ PROTECTIVE RELAYING OPERATED AND TRIPPED
TRANSFORMER #2 IN APPROXIMATELY ONE SECOND AFTER THE TRANSFORMER
#5 TRIP.
SUBSEQUENTLY IT WAS DETERMINED THAT A RAT HAD CAUSED THE FAULT.
THE B ‘BACK FEED’ OPERATED AS DESIGNED AND INITIATED ALARMS THROUGH
SCADA.
ABLE TO ISOLATE THE CIRCUIT IN THE BUILDING AS WELL AS ISOLATE THE FEEDER
IN THE FIELD.
SWITCHING AND RESTORATION WAS COMPLETE IN 90 MINUTES.
26

A3 3-phase fault
December   27,   2012
Trf#5 69 kV bkr opens
All Trf#5 “A” bkrs and B2 open
SUBSTATION   69   KV
DIGITAL   FAULT
RECORDER
T   =   0
27

December   27,   2012
Trf#2 69 kV bkr opens
SUBSTATION   69   KV
DIGITAL   FAULT
RECORDER
T   =   1   second
28

SWITCHGEAR   CIRCUIT   BREAKER   COMPARTMENT
29

LONG   TERM   OPTIONS   TO   ADDRESS   A   POSSIBLE
FUTURE   MAJOR   EVENT   INSIDE   OF   POWER   BUILDING
SHORTLY AFTER THIS EVENT SEVERAL LONG TERM OPTIONS WERE
PROPOSED FOR EVALUATION TO PREVENT OR LESSEN DAMAGE IF A
SIMILAR OF MORE DESTRUCTIVE EVENT WERE TO OCCUR:
• FIRE DETECTION/SUPPRESSION/POWER-DOWN SYSTEM
• CHANGE TO AN OPEN AIR SUBSTATION DESIGN
• ADD SECOND POWER BUILDING SEPARATED WITH FIREWALLS
• MOBILE BREAKER “SIX PACK” TRAILER RESTORATION SCHEME
• REAL TIME CAMERA MONITORING INSIDE OF POWER BUILDING
LATER IT WAS DETERMINED THAT GAS INSULATED SWITCHGEAR (GIS)
HAD SEVERAL ADVANTAGES FOR THIS PARTICULAR APPLICATION.
30

LONG   TERM   PLAN
12.47
KV   GAS   INSULATED   SWITCHGEAR   (GIS)
GIS SYSTEM INCORPORATES VACUUM BOTTLES INSIDE CAST ALUMINUM TANKS
UNDER SF6 GAS PRESSURE AND IS A SINGLE PHASE DESIGN. THEREFORE, PHASE-
TO-PHASE FAULT IS NOT POSSIBLE.
ALL THE LIVE PARTS ARE LOCATED INSIDE THE TANK AND THE GEAR IS SAFE TO
TOUCH.
NO RACKING AND UNRACKING OF CIRCUIT BREAKERS WOULD BE INVOLVED WITH
THE GIS AS OPPOSED TO AIR INSULATED GEAR. THIS WOULD ELIMINATE
RACKING/UNRACKING OF THE CIRCUIT BREAKERS. IF A GIS CIRCUIT BREAKER WERE
TO FAIL IT WOULD BE COMPLETELY CONTAINED INSIDE THE TANK AN NO DAMAGE
WILL BE DONE TO THE BUILDING OR THE OTHER CIRCUIT BREAKERS.
GIS USES CABLE ‘PLUGS’ FOR ALL TRANSFORMER AND FEEDER CONNECTIONS
WHICH ELIMINATES ANIMAL CAUSED FAULT.
SINCE THE HIGH VOLTAGE PARTS ARE INSIDE A PRESSURIZED TANK (SEALED
ENVIRONMENT), NO MAINTENANCE WOULD BE REQUIRED FOR THE LIFE OF THE
CIRCUIT BREAKER. THE MECHANISM IN A CONVENTIONAL MECHANISM AND CAN BE
MAINTAINED LIKE OTHER CIRCUIT BREAKERS.
BACK FEED PROTECTIVE RELAYING SCHEME WILL CONTINUE TO BE USED AS A
PRECAUTION.
31

Circuit
Breaker
CT’s
LONG   TERM   PLAN
12.47
KV   GAS   INSULATED   SWITCHGEAR
‘Back-Feed’ CT’s
32

LONG   TERM   PLAN
12.47
KV   GAS   INSULATED   SWITCHGEAR
‘Circuit Breaker CT’s
‘Back-Feed’ CT’s
33

Distribution   Substation  ‐ Network   Feeder
‘Back   Feed’   Protection
34