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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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Sequence of Events – Temporary Fault
• 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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Sequence of Events – Temporary Fault
TS
F1
F2
F3
DG
Recloser/Breaker - Open
Wye
Delta
HVI
Recloser/Breaker - Closed Transfer Trip
Fuse (Closed) Fuse (Blown)
Fault
• DGIT and generator breakers open
• Fault does not clear
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Sequence of Events – Temporary Fault
• Feeder breaker recloses
• Fuse blows → Fault is cleared → Load is Lost
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Sequence of Events – Temporary Fault
• DGIT recloses within 10 seconds of breaker reclosing
• Generator stays offline
FaultTS
F1
F2
F3
DG
Recloser/Breaker - Open
Wye
Delta
HVI
Recloser/Breaker - Closed Transfer Trip
Fuse (Closed) Fuse (Blown)
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Sequence of Events – Temporary Fault
• Voltage and Frequency is stabilized
• Generator resynchronizes after 5 minutes
FaultTS
F1
F2
F3
DG
Recloser/Breaker - Open
Wye
Delta
HVI
Recloser/Breaker - Closed Transfer Trip
Fuse (Closed) Fuse (Blown)
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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
Sequence of Events – Permanent Fault
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
Sequence of Events – Permanent Fault
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Sequence of Events – Permanent Fault
• 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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Sequence of Events – Permanent Fault
• 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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