3.1 - anti-islanding protection for small generation in ontario - aidan foss

NRCan Peer Review25th March 2008ANF Energy Solutions Inc

Anti-Islanding for SmallGeneration in Ontario

Anti-Islanding Protection for Small Generation in Ontario

Aidan FossANF Energy Solutions Inc.

[email protected]

NRCanNRCan DER InterconnectionDER InterconnectionPeer Review MeetingPeer Review Meeting

2525thth February 2008February 2008



Anti-Islanding Protection

Anti-islanding protection has been found to be a major barrier to the connection of small (<500kW) generation to rural feeders in Ontario

• Above 50% of the minimum feeder load, the general utility requirement is for Transfer trip

• Cost of Transfer trip ($150K-$250K) can be a show stopper



•Generation on feeder shared with other customers•Recloser/switch normally closed•Utility feeder protection may open recloser/switch

DISTRIBUTEDGENERATION

OTHER CUSTOMERS

THEGRID

RECLOSER

VUTILITY FEEDER

The Elephant and the Mouse (1)



•Feeder energized by your voltage•Other customers supplied with your voltage•Need to disconnect as fast as possible, and before …


OTHER CUSTOMERS

THEGRID

HYDROPOWER

CUT

VVUTILITY FEEDER




•Grid voltage wins over your voltage•Grid voltage wave travels into feeder•Risk of generator torque shock and other damage


OTHER CUSTOMERS

THEGRID

HYDROPOWER

RESTORED

V V

UTILITY FEEDER




Current Standards Local Utility Requirement

Disconnect time

<50% Minimum Feeder Load

U/O frequencyU/O voltage

Power Export

>50% Minimum Feeder Load

< 2 sec.(IEEE 1547, CSA C22.3

No. 9)

Varies, but can be< 1 sec.

Fast transfer-trip : $150k - $250kShow stopper for small DG!

Transfer-trip or Alternative : $30k - $50k?

Protection Standards



Terryland Farms Experience



Grid Connection

HV FUSE

GENERATORPROTECTION

INTER-TIE CIRCUIT-BREAKERINTER-TIEPROTECTION

GENERATOR CIRCUIT-BREAKER

TO DIGESTER & POWERHOUSE LOADS

8.3KV / 480V300kVA Yg:Yg

M REVENUE METER

BIOGAS GENERATOR180kW 480V

UTILITY FEEDER 8.3kV

HV DISCONNECT

LV DISCONNECT

LV FUSE



TERRYLAND180kW

PINEHEDGE100kW

RECLOSERS

8.3 kV

STARDALE DS44 / 8.3kV

8.3 kV

))) (((

))) (((TRANSFER TRIP SYSTEM

INITIALLY RERQUIRED BY UTILITY

• Terryland Farm > 50% MFL• Pinehedge Farm < 50% MFL

MINIMUM FEEDER LOAD

~ 240kW

Local Distribution Network



Pole Mounted Reclosers



Anti-Islanding Considerations

• Transfer-trip too expensive – show stopper• Approached NRCan for assistance• Looked for site-specific knowledge that can be used for

proposing an alternative?

• Increasing recloser times / bypassing reclosers – not an option

• Moving reclosers – expensive, did not solve• Voltage blocking – not feasible for pole mounted

reclosers• Rural feeder characteristics?



• Rural feeder load is inductive• Generator set-point to import VArs from the Grid• Loss of the Grid Shortage of reactive power on the feeder

Generator exports VArs• A directional reactive power relay is used to detect and trip

on a change in VAr flow• Tight conventional protections used as back-up

VAr TripLevel

VArSet-point

P

Q

Proposed Anti-Islanding Concept



• Multi functional generator protection relay (18 protections)

• 40Q: directional reactive power protection connected in reverse

Off-the-Shelf Relay



• Computer model development, verification and tuning:– Load rejection and load pick-up tests

• Dynamic analysis of various scenarios:– +50%, +25% & 0% power mismatch

• Field verification:– Islanding detection and disconnection time tests

– Nuisance tripping tests

Validation Test Plan



Simulation Results: 25% mismatch• Load: 245 kW,

pf=0.95 lag• DG: P=+180 kW,

Q=-31 kVAr• Islanding: t=20s

ΔV = 25% drop,Δf = ± 1 HzΔQ = -31 → +80

1 9 .5 2 0 2 0 .5 2 1 2 1 .5 2 25 9

6 0

a) f

(Hz)

1 9 .5 2 0 2 0 .5 2 1 2 1 .5 2 2

0 .8

1

b) V

(p.u

.)1 9 .5 2 0 2 0 .5 2 1 2 1 .5 2 2

0 .1 5

0 .2

0 .2 5

c) P

(MW

)

1 9 .5 2 0 2 0 .5 2 1 2 1 .5 2 2-0 .0 5

0

0 .0 5

0 .1

d) Q

(MV

Ar)

1 9 .5 2 0 2 0 .5 2 1 2 1 .5 2 2

0 .1 5

0 .2

0 .2 5

Time (sec)

e) P

(MW

)

DG bus

DG

DG

Load



19.5 20 20.5 21 21.5 2260

60.5

a) f

(Hz)

19.5 20 20.5 21 21.5 220.85

0.90.95

11.05

b) V

(p.u

.)19.5 20 20.5 21 21.5 22

0.15

0.2

c) P

(MW

)

19.5 20 20.5 21 21.5 22

-0.04

-0.020

0.02d)

Q (M

VAr)

19.5 20 20.5 21 21.5 22

0.14

0.16

0.18

Time (sec)

e) P

(MW

)

DG

DG

Load

DG bus

• Load: 180 kW,pf=1

• DG: P=+180 kW,Q=-31 kVAr

• Islanding: t=20s

ΔV = 15% drop,Δf = + 0.5 HzΔQ = -31 → +10

Simulation Results: 0% mismatch



Directional Reactive

Power Relay

Utility GridRepresentation

DG

Load 1

Load 2

Farm load

PCC

P

Q

•Soft Start to reduce motor transients•VARs measured at generator breaker, but trips inter-tie breaker

Field Test Configuration



Measurement and monitoring devices

Biogas Engine-Generator

Currentfeedback

Field Test Facility



Relay

GridCB

Gen.Current(Inter-tie CB)

Gen.Voltage 0.136 s 0.216 s

Gen= 72-kW, Load = 95-kW, pf=1 (33% mismatch)

Islanding Test 1: Dynamics



Gen= 130-kW, Load = 145-kW, Q=37-kVAr

0.173 s

0.230 sGridCB

Relay

Gen.Current

±0.5HzFreq. setfor Gen.

Islanding Test 2: 10% Mismatch



• System commissioned August 2007• Scheme Implemented as logical AND of kW and kVAr limits• Nuisance trip tests - large motor load starting transient• Significant imbalance – move to 3-phase kVAr measurement

-15

-10

-5

0

5

10

15

20

25

30

35

0 20 40 60 80 100 120 140 160 180 200

kVA

r

Phase APhase BPhase C3-Ph Q

Time (sec.)

Reactive power variations of the Generator (t1: Agitator start-up, Aug. 23, 2007 - 16:05:59)

Trip set-point (40Q relay)

Commissioning



• For all tests, the trip time was less than 0.25 s• Working with the utility as a potential generic

solution for small DG (<500 kW)• Applicable to feeders with inductive load

characteristics• No nuisance trips during commissioning (soft start

on 15-kW agitator motor) but potentially sensitive to motor starting transients

Terryland Summary



CETC-V, ANF Energy Solutions, Genesys, Terryland Farm

Joint Effort to Test the Method



FEPRO FARMS 499kW

12.47kV

3 x 1-PHASE RECLOSERS

BEECHBURG DS44kV / 12.47kV

MINIMUM FEEDER LOAD

~ 500kVA

Fepro Farms Application

450 kVAr

12.47KV / 600V750kVA Yg:Yg



Anti-Islanding Considerations

• Utility: “will be working with the Generator on developing an alternative to Transfer Trip”

• Capacitor banks on the feeder – feeder not inductive at light loads – cannot apply Terryland method

• Recloser time – 2 seconds – suggested that slower transfer trip may be best option

• Experience from other areas of low-cost uni-directional fail-safe transfer trip



Uni-directional Transfer Trip

3 x 1-PHASE RECLOSERS

& WIRELESSINTERFACE

RECLOSERSTATUSES

))) ((( ))) (((

INTER-TIEPROTECTION

INTER-TIECIRCUIT

BREAKER

WIRELESSINTERFACE

Trip the inter-tie breaker if• Any recloser is open• Loss of communication



Old Reclosers

• Substation reclosers are old – do not have status indication

• Replacing reclosers is expensive ($100K+)

• Pulse-based method – demonstrator proposed for an alternate site

• CT-based method – proposed to utility for this site• Response from utility: “Appears to be conceptually OK”• Limited nuisance tripping is OK if this avoids transfer trip



CT-based Proposal3 x 1-PHASE RECLOSERS

RELAY

WIRELESSINTERFACE

))) ((( ))) (((

INTER-TIEPROTECTION

INTER-TIECIRCUIT

BREAKER

WIRELESSINTERFACE

Trip the inter-tie breaker if• Over-current (within recloser setting)• Low current on all three phases• Loss of communication



Low Current Trip

Trip for low current on any single phase• Safe• Potential for high incidence of nuisance tripping due to

current imbalance

Trip for low current on all three phases• Low expected incidence of nuisance tipping• Preliminary studies show little voltage phase angle

difference across a single open phase low damage potential

• Further studies required (Work in progress)



• Key limitations are the presence of the capacitor bank and the type of recloser

• Need to avoid recloser replacement to have an affordable scheme

• Low-cost wireless components are available• Further studies and equipment selection

required

Fepro Summary

3.1 - anti-islanding protection for small generation in ontario - aidan foss

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