IMPACTS OF LARGE
DISTRIBUTED GENERATORS
ON CENTERPOINT ENERGY’S
DISTRIBUTION SYSTEM
Presented by Ed Briggs, P.E.
Manager of Electric Distribution Planning
SWEDE Presentation May 9, 2014
CenterPoint Energy Proprietary and Confidential Information
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PUBLIC AND EMPLOYEE
SAFETY IS THE MOST
IMPORTANT CONSIDERATION
OF DG DESIGN, CONSTRUCTION
AND UTILITY
INTERCONNECTION !
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WHAT IS DISTRIBUTED
GENERATION (DG) ?
Texas PUC Substantive Rule 25.211
An electric generating facility located at a customer’s point of delivery (point of common couple) of ten megawatts (MW) or less and connected at a voltage less than 60 kilovolts (kV) which may be connected in parallel operation to the utility system.
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DISTRIBUTED GENERATION
BY FUEL TYPE
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Total Pending and
Connected DGs
Through 4/16/14
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Large DG (7500+ KW) Statistics
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WHATS DRIVING THE LARGE
DISTRIBUTED GENERATION
INTERCONNECTIONS?
• Emergency Response Service (ERS) or
Demand Response
• Close transition-parallel with the utility grid for less than 1 second (closed transition switching)
• Parallel operation with power export option
• Parallel operation with no power export
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IMPACTS OF LARGE
DISTRIBUTED GENERATION
• LOAD
• VOLTAGE
• POWER FACTOR
• FAULT CURRENT
• CIRCUIT PROTECTION
• LATERAL FUSE COORDINATION
• EFFECTIVE GROUNDING
• RELIABILITY
• SAFETY
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DG SIZE RATING
A GENERATOR NAME PLATE RATING SHOWS
2500 kVA @ 80% POWER FACTOR
• WHAT IS THE DG kW CAPACITY ?
 2000 kW or 2500 kW ?
SAME QUESTION AS ABOVE EXCEPT THE PRIME
MOVER OF THE GENERATOR IS A DIESEL ENGINE
RATED AT 1800kW
• WHAT IS THE DG kW CAPACITY ?
 1800 kW or 2000 kW or 2500 kW ?
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12.47 kV DISTRIBUTION
FEEDER DG STUDY
• 7 GENERATORS RATED AT 2500 kW EACH
(7 X 2500 = 17,500 kW)
• PRIME MOVER DIESEL ENGINE RATED AT
1800kW
• ACTIVE GENERATION = 7 X 1800 = 12,600 kW
• 12.47 kV FEEDER RATED AT 12,960 kW
• DG VOLTAGE CONTROL @ 100%PF
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12.47kV FEEDER PEAK LOAD
10,260 kW 540 kVAR 99.9 PF
SUB
DG
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DISTRIBUTIVE GENERATION
SETUP (PCC IS POINT OF
COMMON COUPLING)
PCC 2
TO SUBSTATION
PCC 1
12.47 kV BUS
2500 kVA TRANSFORMER
2500 kW GENERATOR
480Y277V
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DG VOLTAGE TRIP SETTING
DG TRIPS IF:
VOLTAGE = 126V FOR 30 SECONDS
VOLTAGE = 132V FOR 10 CYCLES
CUSTOMER WANTS TO OPERATE DG
AT 100% PF
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DG ANALYSIS
CNP SUBSTATION VOLTAGE REGULATION IS SET
AT 122V TO 125V
FOUR CIRCUIT MODELING SENARIOS ARE:
 SUMMER PEAK LOADING
• SUB AT 125V
• SUB AT 122V
 OFF-PEAK LOADING
• SUB AT 125V
• SUB AT 122V
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LOCATION AT PCC WITH SUB AT
125 V WITH SUMMER PEAK LOAD
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LOCATION AT PCC WITH SUB AT
122 V WITH SUMMER PEAK LOAD
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LOCATION AT PCC WITH SUB AT
125 V WITH OFF-PEAK LOAD
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LOCATION AT PCC WITH SUB AT
122 V WITH OFF-PEAK LOAD
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LOCATION AT PCC WITH SUB AT 125 V
WITH SUMMER PEAK LOAD & EFFECTS
OF CAPACITOR BANKS
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DG CAN REDUCE THE VOLTAGE AT PCC
BUT RESULTS IN INCREASED kVAR
WHICH RESULTS IN A 394 kVA DEMAND
THUS A $$$$$ MONTHLY BILL
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DURING OFF PEAK SEASON 4 DGs
BACKFEEDS SUBSTATION
TRANSFORMER WITH 2279 kW
Substation
Transformer
Circuits #1 #2
2279 kW
#3
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12.47kV FEEDER PEAK LOAD
10,260 kW 540 kVAR 99.9 PF
DG
DG
SUB
DG
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At PCC with Sub at 125 V with
Summer peak load & DG located near Sub
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At PCC with Sub at 125 V with
Summer peak load & DG located at end of circuit
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DG INCREASES CIRCUIT FAULT CURRENT
AND CAUSES 100T FUSE NOT TO COORDINATE
WITH 65T, MUST CHANGE LATERAL TO A
FEEDER AT CUSTOMER EXPENSE
65T fuse
Without DGs, I
LG max =
With 7 DGs, I
LG max =
2578 A
3976 A
100 T fuse
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DG ELEVATES FAULT CURRENT
ON SUBSTATION BUS AND
ADJACENT CIRCUITS
 A FAULT ON ADJACENT CIRCUIT WILL BE FED BY DG CIRCUIT
AND MAY RESULT IN TWO CIRCUITS OPERATING THUS
IMPACTING RELIABILITY
 LATERAL FUSE COORDINATION WILL NEED TO BE ASSESSED ON
ADJACENT CIRCUITS DUE TO HIGHER FAULT CURRENT
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Line to Ground Fault Currents
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EFFECTIVELY GROUNDED SYSTEM PER
IEEE STANDARD 142
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EFFECTIVELY GROUNDED SYSTEM CHECK ?
CUSTOMER’S HIGHSIDE RESISTIVE
GROUNDING 24 OHM ON 12.47kV SIDE OF THE
TRANSFORMER
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CNP REQUIRES TRANSFER TRIP FOR DGs
OVER 2000 kW. HOWEVER CIRCUIT
SWITCHING CAN SCUTTLE THIS
N.C.
N.O. (TIE)
Sub 1
Utility crew opens the N.C. switch
N.C.
Lateral
DG
Sub 2
Utility crew closes the tie switch
DG will be transferred from a feeder from sub 1 to another feeder from sub 2
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NEXT YEAR’S PRESENTATION DG
ACTUAL DATA VERSUS MODELED
THANK YOU !
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NEXT YEAR
DG ACTUAL VERSUS MODELED
THANK YOU !
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