IMPACTS OF LARGE DISTRIBUTED GENERATORS ON CENTERPOINT ENERGY’S

DISTRIBUTION SYSTEM

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Presented by Ed Briggs, P.E.

Manager of Electric Distribution Planning

SWEDE Presentation May 9, 2014

CenterPoint Energy Proprietary and Confidential Information

SAFETY MOMENT

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) ?

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Texas PUC Substantive Rule 25.211An 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

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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• LOAD

• VOLTAGE

• POWER FACTOR

• FAULT CURRENT

• CIRCUIT PROTECTION

• LATERAL FUSE COORDINATION

• EFFECTIVE GROUNDING

• RELIABILITY

• SAFETY8

IMPACTS OF LARGE DISTRIBUTED GENERATION

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

DG

SUB

DISTRIBUTIVE GENERATION SETUP (PCC IS POINT OF

COMMON COUPLING)

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Utility sourceUtility Source

PCC 2

2500 kVA TRANSFORMER

PCC 1

12.47 kV BUS

TO SUBSTATION

2500 kW GENERATOR 480Y277V

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 VOLTAGE TRIP SETTING

CNP SUBSTATION VOLTAGE REGULATION IS SET AT 122V TO 125V

FOUR CIRCUIT MODELING SENARIOS ARE:SUMMER PEAK LOADING

• SUB AT 125V

• SUB AT 122VOFF-PEAK LOADING

• SUB AT 125V

• SUB AT 122V14

DG ANALYSIS

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

DURING OFF PEAK SEASON 4 DGs BACKFEEDS SUBSTATION

TRANSFORMER WITH 2279 kW

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SubstationTransformer

Circuits #1 #2 #3

2279 kW

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12.47kV FEEDER PEAK LOAD 10,260 kW 540 kVAR 99.9 PF

DG

SUB

DG

DG

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 CURRENTAND CAUSES 100T FUSE NOT TO COORDINATE

WITH 65T, MUST CHANGE LATERAL TO A FEEDER AT CUSTOMER EXPENSE

Without DGs, I LG max = 2578 A With 7 DGs, I LG max = 3976 A

100 T fuse

65T fuse

DG ELEVATES FAULT CURRENT ON SUBSTATION BUS AND ADJACENT

CIRCUITS

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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

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

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Sub 1 Sub 2

DG

N.C. N.O. (TIE)

N.C.Utility crew opens the N.C. switch

Utility crew closes the tie switch

DG will be transferredfrom a feeder from sub 1 to another feeder from sub 2

Lateral

SWEDE 2015

NEXT YEAR’S PRESENTATION DG ACTUAL DATA VERSUS MODELED

THANK YOU !

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NEXT YEARDG ACTUAL VERSUS MODELED

THANK YOU !

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Any Questions ?