Ian Bradley - DG Presentation - APPrO · DG Interconnection Ian Bradley ... • If the low set...

DG Interconnection

Ian BradleyManager – P&C ProgramsHydro One Networks Inc.January 22, 2009

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Outline• Anti-Islanding Protection

– Requirement– Transfer Trip Requirement– New technologies being studied

• DG Interconnection Transformer – New Requirements

• Hydro One Feeder Protections

• Resynchronization of DG facilities to Hydro One

• Example of sequence of events for temporary and permanent faults

• Conclusions

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Anti-Islanding Requirement• Islanding of DG facilities shall not be permitted in Hydro One’s

Distribution System

• Electric island – DG continues to supply HONI customers after HONI has disconnected via breaker/recloser

TS

F1

F2

F3DG

Recloser/Breaker Closed

DG

CB1

CB2 CB3

CB4

Recloser/Breaker Open

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Anti-Islanding Requirement• Islanding of DG facilities shall not be permitted in Hydro One’s

Distribution System

• Electric island – DG continues to supply HONI customers after HONI has disconnected via breaker/recloser

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Anti-Islanding Requirement• Reasons for Anti-Islanding protection

– Prevent Power Quality problems to HONI’s customers

– Prevent Out-of-Phase Reclosing

– Mitigate safety hazards

• Solutions will vary depending on size and type of DG and load profile of feeder– Under/Over Frequency and Voltage protections required.

– Directional overcurrent/power, negative sequence overcurrent, zero sequence voltage, transfer trip may be required

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Transfer Trip Requirement• HONI requires that all exporting DGs be equipped with a Transfer

Trip (TT) signal unless:

– the maximum generation is less than 50% of the minimum feeder load – not

able to sustain island

• Consistent with CSA, international standards & major utility practices

TS

F1

F2

F3DG

Recloser/Breaker

Transfer Trip

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Transfer Trip Requirement• Transfer Trip may be costly for smaller DG installations – especially

when multiple devices need TT to the DG Facility

• Hydro One is working on solutions which will replace the Transfer Trip Requirements for DG facilities interconnecting sized 500kW and below, which include:

– Pulse-based Signaling (Connectivity-based)

– Rate-of-change-of-frequency (ROCOF) – local based

– Vector Surge (Vector Jump) – local based

• Each technology will be evaluated and tested to determine its suitability for use as Anti-Islanding Protection for these projects

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DG Interconnection Transformer (DGIT)• Hydro One has initiated a task force of experts to determine the

most efficient, safe and reliable method of connecting generation to the distribution system

• New standards have been created and will apply to all future DG interconnections

• Issues associated with the DGIT:

– (HV):(LV) Delta:Wye-Gnd – causes damaging temporary overvoltages to Hydro One during ground faults

– (HV):(LV) Wye-Gnd:Delta – adds a ground source to system and desensitizes feeder ground protections

– (HV):(LV) Wye-Gnd:Wye-Gnd – also acts as a ground source and allows harmonics to pass

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DG Interconnection Transformer (DGIT)

• 3-Wire Distribution Systems

– Delta (HV) : Wye-Gnd (LV) DGIT

– Grounding transformers may be required on LV side to limit TOV to DG

– Not a ground source – will not affect Hydro One’s feeder ground protection

– No TOV on Hydro One’s distribution system

– High Voltage Interrupter not a requirement

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DG Interconnection Transformer (DGIT)

• 4-Wire Distribution Systems

– Wye-Gnd (HV) : Delta (LV)

– Neutral reactor required on HV side to limit ground current infeed

– Shall be sized to ensure TOV is limited to 125% of nominal – will not have a TOV

problem

– Is a ground source

– For DG installations greater than 500kW, HVI is required to trip DGIT from system –

eliminating ground source

– For DG facilities smaller than 500kW

• Wye-Gnd (HV) : Wye-Gnd (LV) DGIT will be allowed

• Does not require HVI

• If single phase switching is present upstream – three single phase transformers shall be

used

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Hydro One’s Feeder Protections• Hydro One will utilize distance protection for low set instantaneous phase

and ground protection

• If the low set protections operate, the DGIT and DG shall trip – via Transfer Trip or other approved Anti-Islanding Protections

• DGIT is removed from system – ground source is also removed

• Overcurrent protection will then operate as required – DG’s will not impede feeder protections

• Using this approach and the combination of DGIT configurations, both TOV and ground protection problems have been eliminated

• May enable quicker connections as standard modules are being developed

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Resynchronization• Following a protection operation, the DGIT shall reclose into the

distribution system within 10 seconds

– This will limit the power quality issues associated with DGIT

energization for Hydro One customers

• The generator shall stay offline until voltage and frequency hasbeen stabilized and within limits for at least a period of 5 minutes

• If voltage and frequency are not restored within a period of 5 minutes, resynchronization shall lockout and the generators shall be kept offline until Hydro One operators contact the DG facility

• The DGIT and generator reconnection may need to be staggered if multiple DGs are present on feeder

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Sequence of Events – Temporary Fault

TS

F1

F2

F3

DG

Recloser/Breaker - Open Transfer Trip

Fault Wye

Delta

HVI

Recloser/Breaker - Closed

Fuse (Closed) Fuse (Blown)

• Fault Occurs – ex. Bird/Tree Contact on a lateral protected by fuse

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• Low Set Instantaneous Feeder Protections senses fault – Opens feeder breaker (Fuse Saving Scheme)

• Sends Transfer Trip to DG Facility – to HVI and generator breaker

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TS

F1

F2

F3

DG

Recloser/Breaker - Open

Wye

Delta

HVI

Recloser/Breaker - Closed Transfer Trip


Fault

• DGIT and generator breakers open

• Fault does not clear

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• Feeder breaker recloses

• Fuse blows → Fault is cleared → Load is Lost

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• DGIT recloses within 10 seconds of breaker reclosing

• Generator stays offline

FaultTS

F1

F2

F3

DG


Wye

Delta

HVI



18


• Voltage and Frequency is stabilized

• Generator resynchronizes after 5 minutes

FaultTS

F1

F2

F3

DG


Wye

Delta

HVI



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Sequence of Events – Permanent Fault

• Fault Occurs – ex. Conductor breaks

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• Low Set Instantaneous Feeder Protections senses fault – Opens feeder breaker

• Sends Transfer Trip to DG Facility – to HVI and generator breaker


TS

F1

F2

F3

DG

Recloser/Breaker - Open Transfer Trip

Wye

Delta

HVI

Recloser/Breaker - Closed

Fault

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• DGIT and generator breakers open

• Fault is not cleared after reclose attempts

• Hydro One crews are dispatched to repair line

• After 5 minutes the generator resynchronization will lockout


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• Hydro One repairs line – Fault is cleared

• Operators close Feeder breaker energizing the line

• DGIT recloses within 10 seconds - Generator stays offline

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• Operators contact DG facility

• Generators are restarted manually and synchronized to Hydro One

Summary• The new requirements presented here will allow DGs to connect

with fewer problems, and allow a quicker turn around time.

• They have eliminated two of the major technical barriers faced with interconnection of DGs –TOV and feeder protections

• Hydro One is working hard to determine best practices and ideal solutions to technical problems faced with interconnection of DGs

– Focused on safety, reliability, and minimizing cost to DG Proponents

– Creating modular equipment which can be implemented quickly and efficiently to reduce wait times

Future• The new DG Interconnection Requirements Standard shall be

provided to the public shortly

• Hydro One will continue to develop solutions to enable more generation and overcome other technical and financial obstacles – such as Anti-Islanding Protection for smaller DGs

• P&C Enablement Program for DG Interconnection

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