interconnect protection of dispersed generators chuck mozina beckwith electric co., inc

Interconnect Protection of Dispersed GeneratorsInterconnect Protection of Dispersed Generators

Chuck Mozina

Beckwith Electric Co., Inc.

The Utility Industry

Today: Acquisition and Consolidation


Today: Acquisition and Consolidation


Future: Distribution Generation


Future: Distribution Generation

What Is Interconnection Protection?

What Is Interconnection Protection?

Protection that allows the Independent Power Producer (IPP) to operate in parallel with the utility.

Large non-utility generators do not require specific interconnection protection.

Smaller dispersed DG generators do require specific interconnection protection.

Typical Interconnection Protection

Typical Interconnection Protection

Disconnects the generator when it is no longer operating in parallel with the utility.

Protects the utility system from damage caused by connection of the generator (fault current and overvoltage).

Protects the DG generator from damage from the utility system, especially through automatic reclosing.

Local Loads

Utility System

IPP System

InterconnectionRelay

InterconnectionTransformer

To Utility System

Typical Generator ProtectionTypical Generator Protection

Generator internal short circuits.

Abnormal operating conditions (loss of field, reverse power, overexcitation and unbalance currents).

Local Loads

Challenges for the Protection EngineerChallenges for the Protection Engineer

Seamless integration of DG’S into the

utility protection system despite:

– ownership boundaries

– conflicting objectives of DG owners vs. utility

Making sure protection is operational

over the life of the installation

Utilities Generally Specify Interconnection Protection

Requirements

They typically Include:

Utilities Generally Specify Interconnection Protection

Requirements

They typically Include:

Winding configuration of interconnection

transformers

Utility grade interconnection relays

CT and VT requirements

Functional protection

– 81U/O, 27, 59, etc. (required speed of operation)

Settings of some interconnection functions

Impact of Interconnection Transformer Configuration on Interconnect Protection

Impact of Interconnection Transformer Configuration on Interconnect Protection

Overvoltage caused by ungrounded primary windings

Ground fault current caused by grounded primary

windings

Source feeder relaying responding to secondary

faults at the DG facility

Typical 4-Wire Distribution Feeder Circuit




Pole-top transformer rated for line-to-neutral voltagesexample: 13.2 KV 3 7.6 KV

Ungrounded Interconnection Transformers


LowVoltage(SEC.)

HighVoltage(PRI.)



Problems

Can supply the feeder circuit from an underground sourceafter substation breaker A trips causing overvoltage

LowVoltage(SEC.)

HighVoltage(PRI.)



Problems Advantages

Can supply the feeder circuit from an underground sourceafter substation breaker A trips causing overvoltage

Provide no ground faultbackfeed for fault at F1 &F2. No ground current from breaker A for a fault at F3.

LowVoltage(SEC.)

HighVoltage(PRI.)

Saturation Curve of Pole-Top Transformer

Saturation Curve of Pole-Top Transformer

Many utilities use ungrounded primary windings only if IPP sustains at least a 200% overload on islanding.

Grounded Primary Interconnection Transformers


LowVoltage(SEC.)

HighVoltage(PRI.)



ProblemsLowVoltage(SEC.)

HighVoltage(PRI.) Provides an unwanted ground

current for supply circuit faultsat F1 and F2.

Allows source feeder relaying at A to respond to a secondary ground fault at F3.



Problems Advantages

No ground current from breakerA for faults at F3. No overvoltagefor ground fault at F1.

No overvoltage for ground fault at F1.

LowVoltage(SEC.)

HighVoltage(PRI.) Provides an unwanted ground

current for supply circuit faultsat F1 and F2.

Allows source feeder relaying at A to respond to a secondary ground fault at F3.

Interconnection Protection of Dispersed Generators

Interconnection Protection of Dispersed Generators

Protection Objectives

Loss of parallel operation

Fault backfeed detection

Detection of damaging system conditions

– Open phase condition

– Phase sequence reversal

Abnormal power flow

Restoration

Typical Interconnection Protection for Wye-Ground (PRI.) Interconnection

Transformer


Transformer

LOAD


Transformer


Transformer

Loss of Parallel Detection Over/under frequency & over/under voltage “window” In some applications rater of change of frequency (81R) is used.

Loss ofParallel

LOAD


Transformer


Transformer

Loss of Parallel Detection Over/under frequency & over/under voltage “window” In some applications rater of change of frequency (81R) is used. If feeder load and IPP generation are near a match, transfer trip (TT) maybe required.

Loss ofParallel

LOAD


Transformer


Transformer

Fault Backfeed Removal Detection Not Required for induction generator of small synchronous IPP’s

– Can rely on loss of parallel protection Moderate to large IPP’s

– Phase faults: 51V, 67, 21– Ground faults: 51N, 67N

Fault BackfeedRemoval

Loss ofParallel

LOAD


Transformer


Transformer

Damaging System Conditions Unbalanced currents

– Open conductor/single phase (46)– Phase reversal (47)


DamagingConditions

Loss ofParallel

LOAD


DamagingConditions

AbnormalPower Flow

Loss ofParallel

LOAD

Abnormal Power Flow Enforces interconnect contract

– Prohibits IPP from providing power to utility in violation of interconnect contract


Transformer


Transformer


Transformer


Transformer

Supervises reclosing of A

CASE #1 - Local Load Exceeds GenerationRestoration Practice Interconnection relays trip IPP generator breakers (B&C) When utility restores IPP generator auto synchronize to return to service


Transformer


Transformer


CASE #2 - Local Load Matches GenerationRestoration Practice Interconnection relays trip main incoming breaker (A) When utility restores 25 function (with , F, and V) recloses A to

restore parallel with utility.


Transformer


Transformer


A

Total Interconnect Package Loss of Parallel Fault backfeed removal Damaging conditions Abnormal power flow Restoration


Transformer


Transformer


DamagingConditions

AbnormalPower Flow

Loss ofParallel

LOCALLOAD

25

VT

Restoration

Typical Interconnection Protection for Ungrounded (PRI.) Interconnection

Transformer

Typical Interconnection Protection for Ungrounded (PRI.) Interconnection

Transformer


DamagingConditions

AbnormalPower Flow

Loss ofParallel

25

VT

Restoration

LOCALLOAD

ConclusionsConclusions Interconnection protection will have renewed

importance in the next 10 years.Properly designed interconnection protection

addresses concerns of both DG owners and utility.

This presentation outlines salient points utility and DG owners need to consider when developing protection requirements.

Interconnection transformer configuration plays a pivotal role in interconnection protection.

Digital multifunction relays are an ideal technology for interconnection protection.

interconnect protection of dispersed generators chuck mozina beckwith electric co., inc

Documents

utility system slide

kv slide

consolidation slide

facility slide

installation slide

interconnection functions

local loads slide

distribution generation