Islanding System

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Islanding System in RSP An Overview



Islanding Deliberate act of Isolation of a running Unit/s

with compatible loads to save the Unit/s from

tripping when Grid is having unstable

condition.



RSP Power System..



Islanding Scheme…



Islanding with One unit..



Sensing Islanding Condition …

• At MSDS-II:

– Single Unit Islanding &

– Double Unit Islanding

• Relay 1A & 1B connected to HSL Feeder-1

• Relay 2A & 2B connected to HSL Feeder-2 – MiCOM P341 (Areva Make) numerical relays

• At CPP-II

– Single Unit followed by Double Unit Islanding• FCX Relay connected to 132kV Islanding Bus CVT

– Sensing Under frequency during islanded condition



Islanding Conditions …

• Directional O/C ( E/F) combined with Under

Voltage

– Over Current

• Directional Forward ( towards line)

• IEC E Inv, 300A ( Each Feeder), TMS-0.125 – 150A, 0.125 for One Generator / One Feeder condition

– Under Voltage

• Definite Time

• 52.66 kV ( 70%) Phase- Neutral

• Time Delay- 0 s




• Reverse Power combined with U/F

– Reverse Power

• Directional Forward ( towards line)

• 28.8MW ( Each Feeder) for 5 Sec

– Under Frequency

• 48 Hz for 1.0 Sec

• Pure Under Frequency

– 47.6 Hz for 300 ms

• Rate of change of Frequency – 1.5 Hz /sec ( +/-)

– Time Delay 200 ms

– Inhibit band – 49.5 – 50.5 Hz




• Under Voltage (pure)

– 60 kV ( 80%) ( Phase to Neutral)

– Definite Time ; Time delay 1.5 sec

• Over Voltage – 91.2 kV ( 120%) ( Phase to Neutral)

– Definite Time ; Time delay 2.0 sec

• Voltage Vector shift

– 10 Degree



Sequence Logic …

1A 1B

2A 2B

OR d1 b1

d2/d3

d4

CPP-1 CPP-2DU

SU

TRIP HSL FDR-1 & 2

HSL FDR-1 OFF

HSL FDR-2 OFF

AND d5

MSDS-2

RM-2



Sequence Logic …

OR

d9

d6

RM-1

MSDS-3SU

DU

TRIP

SEC-2 B/C

CPP-1

MSDS-2

d8

CPP-2 U/F

SU

SU

DU



Sequence Logic …

OR

C21 TRIP MD2 LINE

CPP-2

MSDS-2

C22

CPP-1

FCX

DUAND

U1

U2

DU

DU

AND

AND

RH29

AND

G1 G2

AND

AND

OR

U1

U2

U1

U2

U2

U1

SU

SUAND

SUU2U1

TRIP B/C



Synchronisation…



Evolution …

CPP-1-GEN

CPP-1-GRID

RM-2

MSDS-3

MSDS-3

CPP-2 MSDS-2

MSDS-2

I nception

1980

1987

1997

1989-90 RM-1 Gen

RM-1 Grid

33 KV GRID



Evolution of Islanding Scheme …

• Since inception

– Isolation from grid at CPP-I and RM-1 through voltage

dependent U/F relays.

• Independent Relays at CPP-1 and RM-1

• 1987

– CPP-2 units commissioned

– No Islanding scheme was available for CPP-2 units.

• 1989

– Single Unit Islanding scheme commissioned• U/F, -dF/dt & U/V isolation provided

– Scheme suggested by Consultant (TCE)

– Although Double Unit Islanding scheme was provided by consultant, it

was not taken into service.




• 1999

– Islanding on U/V kept defected.

• To prevent isolation followed by tripping of Islanded unit

during U/V caused by internal faults.

• 2000 – DOC Islanding put into service

• Current feedback to grid combined with Under Voltage

initiated isolation

• Isolation of HSL Fdr- 1&2 at MSDS-II

• IEC SI curve for DOC

– DU and SU islanding also included in the scheme.




• 2002

– Numerical Islanding relay installed at MSDS-2

– DOC / DEF combined with U/V used for double

unit isolation.

• 2005

– DOC /DEF combined with U/V implemented for

Single Unit Islanding also.

• 2006 – Islanding scheme as in service now implemented.



Features of Present Scheme…

• Sensing of all islanding conditions shifted to MSDS-2

( Common Coupling point)• dF/dt rise, Over voltage , Over Frequency, Under

Voltage and Vector Shift introduced.

• IEC EI characteristics for DOC/ DEF

– For in-sensitivity to remote end faults

• Directional O/C & E/F relays introduced in grid sideof HSL fdr.

– To prevent tripping in case of grid fault.

• Dynamic relay setting for single Unit/ single Feeder configuration.

• Dedicated Islanding Panel commissioned in MSDS-2



Constraints….

• Post islanding stability of CPP-2 units is not

satisfactory.

– No of failure of Units after successful isolation is very high

– Problems attributed to Governing & Excitation system

• System is not designed from islanding perspective

– No dedicated load connected to generator bus

– All grid faults are terminal faults to CPP-2 generators.

– Transmission & Distribution configuration is inadequate in

isolated condition

– Multi-point isolation.



Constraints…. • Constraints of Islanding Load

– Fluctuating Loads have to be shed during islanded condition

– Manual estimation islanding loads.

– Post islanding load management feature not available

– Failure of islanding due to load-starvation

• Failure of islanding due to non-system faults

– Complicated Sequence logic

– Multiple islanding locations connected by control cabling

– CPP-2 unit status and Grid Power status not available in

islanding scheme



Constraints…

• Difficult synchronization process

– Synchronization facility not available in Common Coupling

point ( MSD-2)

– Multiple operations required for synchronization.

– Multiple asynchronous points• CPP-1 & CPP-2 not running synchronism after

islanding

– Limit on islanding loads even in presence of generation

capability

• Information for Disturbance / Failure analysis not

available



Actions…

• Dedicated control cables between islanding locations

– Status of Grid side CB of HSL feeders and CPP-2 unit CBshall be available

– No. of interposing relays shall be reduced- Islanding

commands shall be transmitted radially.

• Cable Laying job under progress- completion expected by Mar’07

• Redundant Islanding relays

– Ensure 100% sensing of islanding conditions

• Commissioned in Jun’06

• Third HSL Feeder to MSDS-3

– HSM/LHF can run during islanding(if power is available)

– Synchronization shall be easier.

• Job under progress- expected by APR’07

Documents

Islanding System