Singapore?s EMA unveils update on power failure of 29 June 2004
Wednesday, July 14 2004 - 03:34 AM WIB
PART 1 ? GAS SUPPLY FAILURE
Factual Account
1 Gas supply to our power stations was disrupted on 29 June 2004. This led to a loss of about 30% of online generation capacity and blacked out large areas affecting about 300,000 consumers. The blackout started at about 2210 hrs. Power was progressively restored starting at 2226hrs and was completed by 2358 hours.
What Caused the Power Failure?
Pressure regulating valves
2 The gas from Natuna is piped at high pressure (900-1,300 pound per square inch, psi) to a receiving station at Sakra, Jurong Island. The pressure is regulated to a lower delivery pressure (at 570 psi) when it enters our domestic gas network.
3 This pressure is controlled by two pressure regulating valves which work in tandem with each other to provide pressure regulation in the same stream. One backs up the other (ie if one fails to regulate pressure, the other cuts in).
4 If the two pressure regulating valves in one stream fail to work, there is a second parallel stream which is also controlled by two pressure regulating valves working in tandem. This second stream takes over the task of pressure control.
Emergency shutdown valves
5 If the system of pressure regulating valves fails, the emergency valves will be activated to shut down the gas supply to prevent the downstream gas pressure from building up to dangerous levels. The system of emergency valves is critical for public safety.
Failure of a pressure regulating valve
6 Investigations to date reveal that a fault developed in a component called a solenoid controlling one pressure regulating valve. Water was found in the solenoid, which could have caused it to become defective. ConocoPhilips is still investigating whether this is the cause of the fault. The defective solenoid would have caused the affected pressure regulating valve to behave in an unexpected way, which brought about the failure of the pressure regulating system. The emergency shutdown valves were activated and shut down as designed, to prevent pressure in the gas system from rising to dangerous levels. This caused a disruption in the gas supply.
What has been done to date?
7 With the defective pressure valve in one stream (Stream 2), pressure control has been switched to the other parallel stream (Stream 1) to reactivate the pressure regulating system. The pressure valves in Stream 1 are being carefully monitored and have been calibrated to ensure that Stream 1 will not suffer the same system failure as Stream 2.
8 In the meantime, the faulty solenoid was checked and was replaced on 4 Jul 2004. All the other solenoids (except in Stream 1) have also been checked and confirmed to be in proper condition. Pressure control will be switched back to Stream 2 soon, and the remaining two solenoids in Stream 1 can then be checked.
9 While investigations have established that a faulty solenoid caused the failure, it has still not been established definitively why the failure occurred. Until the reasons for the failure can be ascertained, the pressure regulating valves will be closely monitored and control of these valves will be switched to manual control if necessary.
What else is being done?
10 EMA has directed ConocoPhilips to investigate why the solenoid became faulty. ConocoPhilips will also have to investigate how to improve the design logic of the pressure regulating system, so that such valve failures in future will not cause the emergency shutdown. In addition, it will also conduct a comprehensive review of the system from the gasfields to the gas receiving system. A report will be submitted to EMA as soon as possible.
PART 2 ? POWER GENERATION FAILURE
Power generators are designed to cope with gas supply disruption
11 All the gas turbines of the three power stations (viz Seraya, Tuas and SembCogen) which drew gas from Natuna were affected by the gas supply shutdown. They are designed to be able to operate with gas or diesel. If the gas supply fails, the turbines should switch to diesel. The power stations are required to stockpile diesel, and can run on diesel indefinitely.
12 There are two ways the gas turbines can switch to diesel. Firstly, the power stations can switch off the turbines, change the fuel from gas to diesel and then restart. As the restart takes about 1.5 hours, there would be a temporary loss of power. The second way, which will avoid blackouts, is for the turbines to switch to diesel while still running with gas, without shutting down and restarting. This is called "hotswitching". The power stations have to hotswitch before the gas runs out. It normally takes about 8 to 12 minutes to hotswitch. On average the gas in the pipelines runs out in about 10 minutes. The time available varies depending on how much residual gas is in the system and the rate at which gas is being drawn. Hence, hotswitching is done under difficult conditions and tight pressure of time.
Hotswitching was done successfully several times in the past
13 There have been previous occasions when the emergency shutdown valves were activated, and the hotswitch to diesel worked successfully. No blackouts were experienced then.
14 In addition, the power stations are required to practice hotswitching on a quarterly basis, and they in fact hotswitch their turbines more frequently than this.
However hotswitching failed on 29 Jun 04
15 On 29 Jun 2004 when the gas failure occurred, Seraya managed to hot-switch one of their two gas turbines. Seraya reported that they ran out of gas before the second turbine could be switched. SembCogen managed to hot-switch 2 turbines into operations but both tripped out about 5 minutes later. Tuas was in the process of hot switching their two gas turbines when the gas ran out.
What has been done to date?
16 After power was restored, the power stations ran tests and confirmed the turbines could be hotswitched and that the hotswitching equipment were working properly.
What else is being done?
17 EMA is investigating why the turbines tripped and will review the standard operating procedure on hotswitching. EMA will explore the feasibility of providing gas backup during times of gas disruption. This could include leveraging on the existing gas pipeline system or gas storage, to tide the gas turbines over the interval needed to hotswitch successfully.
Power generators need time to restore power supply
18 The turbines are brought back into the electricity system one at a time. As generation capacity is brought back on line, power can be restored and this is done progressively. After each restoration, the system has to be allowed to stabilise before the next restoration is done. This is to prevent the system from being overloaded. Restoration cannot therefore be immediate.
PART 3 ? ENERGY SECURITY OPTIONS
19 At present, the installed generation capacity comprises a good balance of fuel types, with 60% capacity in oil-fired steam plants and 40% in gas plants. Even in the event of a prolonged disruption in gas supply, our energy security will not be compromised. We can run on steam plants to meet demand. We can also switch the gas plants to run on diesel for as long as necessary. However, there will be a cost impact as the price of electricity from oil and diesel will be 10% to 20% higher than gas.
20 Against this background, the power failure on 29 Jun 2004 was a temporary disruption caused by a sudden and acute failure of the gas supply which the power stations could not respond to in a timely way. Given sufficient time, the system was able to recover itself. However, such temporary disruptions have serious impact on the economy and pose great inconvenience to the public. EMA will comprehensively review what measures are needed to strengthen the performance of the energy market, and penalize players who fail performance standards.
Short to Medium Term Measures to Reduce Vulnerability of Power Generation to Supply Failure of Piped Gas
21 At least two measures are being considered to improve the robustness of the generation system in the short to medium term.
Two pipelines for each power station
22 Firstly, discussions are underway to establish the feasibility of ensuring the three major power stations (ie Senoko, Seraya and Tuas) have access to gas from at least two gas pipelines. This will provide gas supply redundancy should one pipeline fail.
23 Senoko already has two pipelines supported by gas from Sumatra and Petronas (Malaysia). Seraya?s current pipeline from Natuna gas will be complemented by a second pipeline taking Sumatra gas ? the pipeline has been laid and is being commissioned. Similarly, Tuas which is currently taking gas from Natuna, is planning its second pipeline to take gas from Sumatra, which will be in place by around mid 2005.
24 Engineering studies are being done to work out how one pipeline can be used to seamlessly support the other if it fails. Hotswitching to diesel will still be needed as the healthy pipeline is not likely to be able to provide for long the large amount of gas suddenly needed to support the failed pipeline. However, even temporary support from the second pipeline will give much more time for the gas turbines to hotswitch.
Allowing interconnection of the two gas pipelines
25 The second measure under consideration is to allow the interconnection of the Natuna and Sumatra pipelines so that in a prolonged shutdown of one pipeline, lost supply can to some extent be made up for by drawing from the other pipeline.
26 EMA is discussing this option with the market players. However, interconnection will take time to effect. As the two pipelines operate at different gas pressures and are under different commercial contractual frameworks, a number of technical, regulatory and commercial issues have to be sorted out before a decision can be taken on interconnection.
Longer Term Option
27 EMA is studying the viability of an LNG facility. From the security perspective, the facility will open access to natural gas from anywhere in the world and will provide LNG stockpile. EMA has received good feedback from industry players on the LNG project, and is finalizing the tender specifications for a feasibility study, which will be called in Jul 2004. The study will assess how best to structure the project to optimize the long term economic and financial viability of the LNG infrastructure, and to minimize the cost on the system. If approved, the LNG facility should be operational after 2010.
PART 4 ? PENALTIES
28 EMA will fine a licensee if it has contravened regulatory requirements. However, investigations are still ongoing, and it is premature for EMA to decide on whether and what penalties to impose.
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For further enquiries, please contact:
Mrs Choo Wai Chan, Head (Corporate Communications)
Tel: 68358011 (O) 68358020 (Fax) 98180212 (Hp)
Email: choo_wai_chan@ema.gov.sg
Ms Angela Soo, Senior Officer (Corporate Communications)
Tel: 68358012 (O) 68358020 (Fax)
Email: angela_soo@ema.gov.sg