SEMINAR ON ISLANDINGBY

PAWAN

What is islanding?

Normally all Power generators are interconnected to form a network called ‘GRID’.

Some times it so happens for a generator to come out of grid, either due to disturbance in grid or due to some other internal reasons. When generator gets disconnected from the grid it is ‘ISLANDED’.

The advantages of Islanding in our network:

Unit tripping can be avoidedTripping of major critical loads in steel plant & JPOCL can be avoidedGeneration loss can be avoidedOil consumption can be reduced or avoidedIf other unit got tripped, it can be restored fastIslanded unit can be connected back to grid much faster, once grid disturbance is cleared.`

How islanding happens?

In our network detection of islanding at 220KV will be done under the following conditions:

o Sensing of open condition of Bus Couplero Sensing under voltage in Bus-2 (islanding bus). Settings are at

75% with 1.5 sec time delay & 73% instantaneouso Under frequency setting is at 47.6 Hz with 2 sec time delay &

47.5 Hz instantaneouso Over frequency setting at 51Hz with dF/dt of 0.5 Hz/seco Sensing of no power flow <2% in both lines with dF/dt 2 Hz/sec o Sensing of Line-1 , Line-2 and either of ICT-1 220KV or 400KV

breakers

Scenario generation & loads before Islanding:

GT-1, CPP-2, ST-1, ST-2, T-1, T-2,T-3,T-4, T-7, T-8 & T-9 will be connected to BUS-2 (Islanding Bus)

GT-2, T-5, T-6, T-10, L-1, L-2, ICT-1, ST-3 & ST-4 are connected to BUS-1 (non-islanding bus)

CPP-1 will be selected either in mode-1 or mode-2 depending upon their gas availability. Mode-1 will trip CPP-1 in case of islanding and Mode-2 will bring it to house load.

CPP-2 has been chosen to put in parallel islanding along with one of our unit. Depending upon the CPP-2 generation and BF-3 status, following modes has been incorporated

In case of islanding & bus coupler open, a hard wired logic provided to trip both the 220KV lines.

Non-islanding unit tripping on under frequency is provided at 0.5Hz/sec with arming at 51HZ. (Frequency reference for this protection is provided with BUS-1 PT supply).

Generation JSWEL CPP-1 CPP-2 Net Gen Loads

Mode-1 CPP-2 Unit Under Shutdown 120 0 0 120 0

Mode-2 CPP-2 Unit Under Shutdown 120 0 0 120 0

Mode-3 Boiler 9 at CPP-2 Down 120 0 50 170 50

BF-3 Down 120 0 60 180 49

Normal generation at CPP-2 120 0 107 227 88

Normal MODE-1 MODE-2 RemarksShutdown

Yes/No

Pellet plant 32 0 32As per present MODE-1 islanding NO

Sinter plant 8 0 8 Waste Gas fan off NO

Cx1 9.5 0 9.5 De-dusting off NO

Cx2 9.5 0 9.5 NO

BF1 6 0 6 NO

BF2 6 0 6 NO

BOFCCP 17 0 17 De-dusting off NO

HSM 20 0 10 Aux TR-2 Feeder Trip NO

CRM (8 MW) - 0 - NO

RMHS (5 MW) - 0 - NO

BOC-1 (18 MW) - 0 - NO

JPOCL Tr-3 37 0 37 NO

JPOCL Tr-4 37 0 37 One BLAC off NO

Ancilaries (10 MW) - 0 - NO

Cement 2 0 2 NO

Township/JSH 2 0 1 NO

Co-3 12 0 5 NO

198 0 180

239

Mode-1 Mode-3

CPP-2 Shutdown

CPP-2 <90(50 MW) Blr-9

S/D

CPP-2 <90(50 MW) BF-3 S/D

CPP-2> 90 MW

BF-3 50 0 50 11 50

SINTER-2 12 0 0 0 0

SMS-2 20 0 0 20 20

BAR MILL 13 0 0 0 0

WRM 11 0 0 0 0

BOC-2 35 0 0 18 18

141 0 50 49 88

Mode-4

Islanding Loads of 4 MT (Loads in MW)

Islanding loads of 7MT (Loads in MW)

Mode-4

Consequences Islanding:1. Bus coupler will go for trip.2. Post islanding, 130MW unit will go to speed mode & CPP-2 will

remain in load mode. 3. In islanded network, at any point of time if CPP-2 has to supply

steam to steel plant, additional load throw-off has to be initiated at MSDS. If MSDS is not initiating, then either TR-3 or TR-4 loads can be cut-off JSWEL end in concurrence with MSDS.

Islanding detected signal will enable islanding unit EHTC:

To change over from LOAD to SPEED control A speed reference set point will be generated from EHTC based

on below formulaNR = NRTD = One hour average actual speed + ((Actual load / 150 )*0.04)3600 + 18 rpm

NRTD value is limited to 3088.90 rpm on upper side and 289.20 rpm on lower side. NRTD will be fast tracking NR in speed control mode.

Islanding detected signal will annunciated in control room, MSDS control room & JPOCL.

Operator Actions Post Islanding: Immediately after islanding, ensure fuel input is marginally

more to boiler than required for islanding load. Depending upon the islanding load & Throttle pressure, HP

Bypass should be kept open close to 15%. Match the HP Bypass fixed pressure set point to actual pressure & put HP Bypass in manual. Reduce the HP Bypass SP slowly as per requirement, to keep open the HP Bypass.

If unit is running on full coal, as a measure of precaution oil support should be taken.

Download Speed Ref SP in Speed ref D/L block with that of NRTD

Further regulation in speed can be effected through the increase /decrease arrow in speed ref D/L station. It is to be noted that during the increase in frequency load will increase and accordingly fuel has to be increased.

ISLANDING CHECK LIST:

Islanded unit is running in speed mode Bus coupler, L-1 & L-2 breakers are in open condition Drum level in normal limits, if required take S/B BFP in

service Observe for actual speed, if it dropping trend continuously,

inform to cut out portion of complex load For any drop in network frequency, EHTC will try to

maintain the frequency SP by injecting more steam flow through CV. At that point of time fuel should be sufficient in the boiler to cater for demand. Hence fuel input, frequency & pressure should be continuously monitored by operator

Islanding bus frequency fluctuation should be less 0.5 Hz / min

Generator PF and MVAR are normal All equipments are in service / healthy

CASE-1: When Bus-2 is live and Bus-1 is live through ICT If islanding is successful and bus-2 is live then reset islanding

relays at islanding panel. With resetting of Islanding panel the trips for Bus-Coupler, Line-1 &

Line-2 shall be off. Reset all master trip relays. Synchronize bus-coupler with Bus-1 (Live Line Live Bus) Talk with lingapur and get the lines back-charged. After getting clearance from Lingapur & LDC charge lines one at a

time. (Live Line Live Bus)CASE-2: When Bus-2 is live and Bus-1 dead (When ICT is out) If islanding is successful and bus-2 is live then reset islanding

relays at islanding panel. With resetting of Islanding panel the trips for Bus-Coupler, Line-1 &

Line-2 shall be off. Reset all master trip relays. Switch off all breakers on Bus-1. Physically check bus-1 and check for bus-bar differential or LBB

operation. Talk with lingapur and get the lines back-charged. After getting clearance from Lingapur & LDC charge lines one at a

time. (Live Line Dead Bus). Switch ON ST-3 & ST-4 after ensuring their LT incomers are OFF. Synchronize Bus Coupler with Bus-1 (Live Line Live Bus)

CASE-3: When Bus-2 is live and Bus-1 dead (When ICT was charged initially) If islanding is successful and bus-2 is live then reset islanding relays at

islanding panel. With resetting of Islanding panel the trips for Bus-Coupler, Line-1 & Line-2

shall be off. Reset all master trip relays. Switch off all breakers on Bus-1. Physically check bus-1 and check for bus-bar differential or LBB operation. Charge ICT Charge ST-3 & 4 after ensuring their LT incomers OFF. Synchronize Bus-2 with Bus-1 thorough bus coupler. Get back feed from lingapur and get clearance from them to synchronize

lines.CASE-4: When Bus-2 is dead and Bus-1 live (When ICT was charged) If islanding is un-successful and bus-2 is dead. Bus-1 is still alive with ICT. Ensure 220KV Line breakers have tripped post islanding. Changeover PT supply of Islanding panel to Bus-1. Reset all islanding

relays. Trip all breakers on Bus-2. synchronize B/C with Bus-2 ( Live line dead bus)

Contact lingapur to get back feed and charge one line on Bus-1 ( Live line live Bus).

CASE-5: When Bus-2 is dead and Bus-1 live (When ICT was charged) and 220KV Lines not available

If islanding is un-successful and bus-2 is dead. Bus-1 is still alive with ICT. Ensure 220KV Line breakers have tripped post islanding. If 220KV Lines are

not available open their closed isolators. Changeover PT supply of islanding panel to Bus-1. Reset all islanding relays.

Ensure as per Annexure-I Trip all breakers on Bus-2. Synchronize Bus Coupler with Bus-1 (Live Line dead Bus).CASE-6: When Bus-2 is dead and Bus-1 dead (When ICT was out) If islanding is un-successful and bus-2 is dead. Bus-1 will also go dead. Ensure 220KV Line breakers have tripped post islanding. Switch-off MCB’s provided in Line-1, Line-2 & B/C islanding trip circuit. Trip all breakers on Bus-1 & Bus-2. Take clearance from Lingapur and get backfeed for one of the lines and

charge one line on Bus-1. ( Live line dead bus) Changeover PT supply of Islanding panel to Bus-1. Reset all islanding relays.

Ensure as per Annexure-I Contact lingapur to get backfeed and charge other line on Bus-1 ( Live line

Live Bus). Synchronize Bus Coupler with Bus-1 (Live Line dead Bus).

Normalization: Ensure the grid conditions are stable & clearance obtained

for synchronizing the bus coupler Reset islanding master trip relay (in islanding panel at MSDS)

& ensure islanding detected alarm gets reset in ECP in CR. Islanding cut out should not be done without resetting the relay at MSDS.

Match the speed reference D/L set point with that of NRTD & after matching synchronize the machine by closing the Bus Coupler.

Check the actual load of machine after synchronization. If the load is less than 45 MW, Increase the Load with Speed

Ref D/L Block, Load the machine more than 50 MW. Set the load reference using Load reference D/L block such

that the sum of load reference matches the Actual load. Reset ISOLATED GRID at EHTC 2 graphic (now it will not

reset until Master trip relay is reset, hard wiring done in both units).

Change over Turbine Control from SPEED to LOAD AT EHTC 2 graphic (now change over will not happen until ISOLATED GRID is reset).

Keep HP Bypass in AUTO & load the machine to full Cut-in Islanding as per requirement

Learning from previous islanding incidents:

On 22/04/08 Islanded unit (U#2) tripped due tripping of feeder on phase failure. Later over load relay settings of feeders are reviewed. As preventive action sufficient oil support should be taken irrespective of available fuel.

On 01/07/08 Unit#1 got islanded while cutting in islanding, as Bus coupler open feedback is persisting. As precautionary measure, one additional alarm K35 relay operated hooked up in DCS to annunciate the operator. If K35 relay acted alarm is persisting, islanding should not be taken in service.

THANK YOU ALL