BHUTAN POWER CORPORATION LIMITED TRANSMISSION DEPARTMENT SYSTEM COORDINATOR OFFICE THIMPHU : BHUTAN
CONTINGENCY PLAN & OPERATION PROCEDURES
TABLE OF CONTENTS Sl. No. 1.
Page No.
WESTERN CONTINGENCY PLAN AND OPERATION PROCEDURE ................................................. 2 1.1
2.0 2.1 2.2 2.3 2.4 3.0
SUPPLY SYSTEM UNDER NORMAL CONDITION ......................................................................... 2 BUS CONFIGURATION.................................................................................................................................. 2 220KV SEMTOKHA SUBSTATION ................................................................................................................ 2 220KV CHHUKHA SWITCHYARD ................................................................................................................ 2 220KV RURICHHU SUBSTATION ................................................................................................................. 2 400kV MALBASE SUBSTATION ...................................................................................................................2 FAILURE OF BOTH 220KV RURICHHU-SEMTOKHA AND 220KV CHHUKHA-SEMTOKHA FEEDERS........................................................................................................................................................... 3
3.1
OPERATION PROCEDURE FOR ABOVE LINE FAILURE : ............................................................................... 3
4.0
FAILURE OF 220KV RURICHHU – SEMTOKHA FEEDER: ................................................................... 3
5.0
FAILURE OF 220KV SEMTOKHA – CHHUKHA LINE............................................................................ 3
6.0
COMPLETE BLACKOUT AT 220KV SEMTOKHA SUBSTATION ........................................................ 4
6.1 7.0
OPERATION PROCEDURE FOR THE ABOVE B LACKOUT .............................................................................. 4 FAILURE OF ANY ONE OF 220KV CHHUKHA – BIRPARA LINE DURING THE PEAK GENERATION .................................................................................................................................................. 4
7.1 8.0 8.1 9.0 9.1
OPERATION PROCEDURE FOR DECOUPLING OF 220KV MALBASE BUS ..................................................... 4 FAILURE OF BOTH 220KV D/C CHHUKHA – BIRPARA LINES DURING PEAK GENERATION . 5 OPERATION PROCEDURE FOR ABOVE LINE FAILURE ................................................................................. 5 ALL 220/66KV TRANSFORMER TRIPS AT MALBASE SUBSTATION ................................................ 5 OPERATION PROCEDURE TO AVOID THE ABOVE PROBLEM ....................................................................... 6
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1.
WESTERN CONTINGENCY PLAN AND OPERATION PROCEDURE
1.1
Supply system under Normal Condition
Under normal condition irrespective of seasons, the supply system for the western grid will be kept as follows: 1. The 66kV Chukha – Semtokha feeder shall be kept in ring system. 2. The 66kV Rurichhu – Lobeysa – Semtokha feeder shall be kept in ring system. The overloading of this line will be addressed by the load shedding scheme installed at Basochhu end 3. The 66kV Chhukha – Phuentsholing feeder shall be kept in ring with 66kV Phuentsholing – Malbase line. This feeder will cater to all the load requirements in Gedu, Phuentsholing and Gomtu substations. 2.
Bus configuration
With the bus coupler remaining healthy, the bus configuration shall be kept as follows. 2.1
220kV Semtokha substation
a. The 220kV Chhukha - Semtokha feeder and the 220kV Rurichhu - Semtokha feeder shall be connected to bus A and B respectively. b. The two Nos. 20 MVA, 220/66kV transformers shall be connected to bus A and B respectively. c. The bus coupler shall be kept closed. 2.2
220kV Chhukha Switchyard
a. Three generating units along with all the 220kV export feeders (220kV Chhukha – Birpara feeder No. I, II and III) shall be kept on one bus (say bus A), while one generating unit along with Bhutan loads (220kV Chhukha – Semtokha feeder and two Nos. 20MVA, 220/66kV, transformers shall be kept on the other bus (say bus B). b. The bus coupler shall be kept closed. 2.3
220kV Rurichhu substation
a. The Lower Stage generators along with the 220kV Rurichhu – Semtokha feeder shall be kept on Bus A while the 30MVA ICT shall be kept on the other Bus B. b. The bus coupler shall be kept closed.
2.4
400kV Malbase substation
a. The 400kV Tala – Malbase feeder and 400kV Malbase – Siliguri feeder shall be on 400kV Bus A, while both 400/220kV 200MVA ICT shall be on 400kV Bus B. b. The tie breaker shall be kept closed Page 2 of 6
c. The 220kV Chhukha – Malbase feeder and 220kV Malbase – Birpara feeder shall be kept on 220kV Bus A, while the 400/220kV 200MVA ICT along with the Bhutan load (both 220kV Malbase – Singhigoan feeders and all 220/66kV transformers) will kept on 220kV Bus B. d. The bus coupler shall be kept closed.
3.0 Failure of both 220kV Rurichhu-Semtokha and 220kV Chhukha-Semtokha Feeders
If there is supply failure from 220kV Rurichhu and 220kV Chhukha to Semtokha substation, Thimphu will still be supplied from 66 kV ring system. In such situation, the Shift In-charge at 220kV Semtokha substation shall ensure that the 66kV lines do not get over loaded. This could be achieved by prioritizing the 33kV and 11kV outgoing feeders and adopting load shedding procedures till the system gets normalized. The prioritizing of the supply feeders may be done on a daily basis depending upon the situation.
3.1
Operation procedure for above line failure:
During the above lines failure, if the 66kV Rurichhu – Semtokha line via 66kV Lobeysa substation also fails, the following procedure shall be followed. a. Shift In-charge at 220kV Semtokha substation should call the Shift In-charge at CHP and BHP regarding the nature of the problem. b. Shift In-charge at 220kV Semtokha substation shall immediately extend the supply to Basochhu in coordination with the Rurichhu substation in charge and then the units at BHP shall be synchronized at their end. c. After the restoration of both 220kV Semtokha – Chhukha line and 220kV Rurichhu – Semtokha line, shift In-charge at 220kV Semtokha substation should sent the information regarding the line failure and restoration of the line to Shift In-charge of System Coordinator Office.
4.0
Failure of 220kV Rurichhu – Semtokha Feeder:
If the 220kV Rurichhu – Semtokha line fails with 66kV Rurichhu – Semtokha line via Lobeysa substation remaining healthy, the BHP has to back down its generation till its total generation is equal to carrying capacity of the 66kV Rurichhu – Lobesa line during peak seasons when the total generation is more than the 66kV Rurichhu – Lobesa line carrying capacity. Note: Thimphu load including Lobesa substation load is around 31MW which is more than the carrying capacity of 66 kV Rurichhu – Lobesa line, considering the CT Ratio connected to 300Ampers.
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5.0
Failure of 220kV Semtokha – Chhukha line
If the 220kV Semtokha – Chhukha line fails along with failure of 66kV Rurichhu – Semtokha line during the peak season, the BHP has to back down its generation till its total generation is equal to total capacity of the 2x20MVA, 220/66kV transformer at Semtokha substation.
6.0
Complete blackout at 220kV Semtokha substation
6.1
Operation procedure for the above blackout
If complete power blackout occurs at 220kV Semtokha substation, the following procedures shall be follow. a. The Shift In-charge at 220kV Semtokha substation shall call the Shift In-charge at CHP and BHP regarding the nature of the problem. b. The Shift In-charge at 220kV Semtokha substation shall immediately open all the incoming feeder breakers (i.e. 220kV Chhukha – Semtokha, 220kV Rurichhu – Semtokha,). c. If there is no problem in Indian grid and no problem in CHP, then CHP shall immediately extend the grid supply to Semtokha. Then the supply shall be extended to Rurichhu substation and BHP shall then synchronize with the grid. d. Incase of Indian Grid failure with CHP or BHP being pulled out, the Shift In-charge at CHP control room shall first try to get feedback supply from Indian Grid, if supply is available at Birpara and extend it up to Semtokha substation, before initiating to normalize its machines (If they have completely tripped). e. Incase Indian power supply is not available then the Generating companies (either CHP or BHP) shall normalize the supply system to Thimphu immediately in coordination with Shift In-charge, 220kV Semtokha substation. f. The shift In-charge, 220kV Semtokha substation shall ensure that after complete supply blackouts, load is gradually applied in consultation with the Shift In-charge at the source of supply. g. After the complete restoration of the Thimphu supply the two generating stations can synchronize their supplies at either end. h. The Indian grid shall be synchronized at Chhukha end.
7.0
Failure of any one of 220kV Chhukha – Birpara line during the peak generation
During the peak generation, when one of the 220kV Chhukha – Birpara feeder trips, the 220kV bus coupler Breaker at Malbase substation should be opened for equal sharing of load between the 220kV Chhukha – Birpara line and 220kV Chhukha – Malbase line.
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7.1
Operation procedure for decoupling of 220kV Malbase bus
Till such time, decoupling of the 220 kV bus at Malbase cannot be done automatically, the following procedure will be followed. a. Immediately after the tripping of one of the 220kV Chhukha – Birpara line, the Shift Incharge of CHP will inform the Shift In-charge of Malbase substation regarding the nature of the problem. b. Shift In-charge of Malbase substation will open the 220kV Bus coupler breaker if the 400kV supply is available and inform the CHP and System Coordinator Office. c. After the normalization of the 220kV Chhukha – Birpara line, the CHP Shift In-charge will inform the Shift In-charge at Malbase substation. d. Shift In-charge at Malbase substation will close the 220kV Bus coupler breaker and inform the CHP and System Coordinator Office.
8.0
Failure of 220kV D/C Chhukha – Birpara lines during peak generation
The maximum power which can be loaded from the 220 kV Chhukha – Malbase line which is Zebra Conductor shall be nearly 200MW considering the current carrying capacity of 620 o Amperes at ambient temperature 40 C and power factor of 0.85, the final temperature of o conductor is 60 C. 8.1
Operation procedure for above line failure
If 220kV D/C Chhukha – Birpara line trips during peak seasons, when the total generation from CHP and BHP is more than the total line carrying capacity of 220kV Chhukha – Malbase line and 66kV Chhukha – Phuentsholing line after supplying Thimphu, Paro and Haa loads. The following procedure shall be followed. a. Shift In-charge at CHP shall inform the Shift In-charge at BHP regarding the nature of the problem and instruct to reduce their generation. b. Shift In-charge at CHP shall maintain the generation such that total generation from CHP and BHP is equivalent to 200MW power flow through the 220kV Chhukha – Malbase Feeder – III and 20MW power flow through 66kV Chhukha – Phuentsholing line. c. Immediately after normalization of 220kV D/C Chhukha – Birpara line, the Shift Incharge at CHP should inform Shift In-charge of BHP and System Coordinator Office regarding the normalization. d. Shift In-charge at BHP may increase their generation.
9.0
All 220/66kV Transformer trips at Malbase substation
When the 66kV Chhukha – Phuentsholing and 66kV Phuentsholing – Malbase are in ring system and if all the 220/66kV transformer at Malbase substation trips, then total loads of Pasakha industrial load along with Phuentsholing, Gedu and Gomtu load will flow through the 66kV Chhukha – Phuentsholing line, thus over loading the line. Page 5 of 6
9.1
Operation procedure to avoid the above problem
In order to avoid the overloading of the 66kV Chhukha – Phuentsholing line, the following procedure shall be followed: a. Shift In-charge at Malbase substation will intimate the Shift In-charge at Phuentsholing substation. b. Shift In-charge at Malbase substation will immediately hand trip the 66kV Malbase – Phuentsholing feeder after intimation to CHP and System Coordinator Office. c. After restoration of the 220/66kV transformers at Malbase substation, then Shift Incharge at Phuentsholing may charge back the 66kV Phuentsholing – Malbase line after intimation with Shift In-charge at Malbase substation, CHP and System Coordinator Office.
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