Friday, June 10, 2005

Power blackout in Dubai:: Gulf News

Thursday's power blackout in Dubai affected one million people; power began to be restored after four hours. Service to all customers was restored within eight hours.

Temperatures on the day were 41C (104F).

The equipment failure has been traced to a fault in a transmission substation. To protect a fault in one location from damaging equipment in other parts of an interconnected system, power systems are designed to shutdown surrounding equipment. In some conditions - such as when customer usage at the time is high - this can result in major blackouts. It takes time to bring the system back up, and it is done in stages. Thursday's outage in Dubai followed this classic pattern. Shutdowns are of course preferred to damaged equipment - both result in blackouts and the latter means a longer blackout.

Dubai's power system relies on natural gas turbines for power generation. Gas turbine generators are small in comparison to coal-fired generators or nuclear generators. Also, in comparison to coal or nuclear, they can be turned on and off easily. These are features that happen to simplify the problem of bringing a power system back up following an extensive outage in the system such as occurred in Dubai yesterday.

Power systems are interconnected by a transmission grid. The purpose of interconnection is to lower cost of generation and to enhance reliability. Imagine a system where each neighborhood had its own generator and neighborhoods were not interconnected. First, it would not take advantage of the likely possibility that one larger generator shared by two neighborhoods would have cost advantages. Second, if a generator fails in one neighborhood, your fellow neighborhoods cannot lend a hand by generating more power and transmitting it to you.

Under most conditions, interconnection is your friend. But under some conditions - like those that occurred in Dubai on Thursday - a failure in one part of the system is transmitted to the rest of the system.

When technicians study a major power outage they identify the state of the system at the time of the outage. How heavy was demand? Was it particularly heavy in one area? Were some parts of the system - transmission or generation - offline at the time of the fault? Answers to these questions lead to recommendations for physical changes in the system and for changes in operating procedures.

Sharjah City, which shares a long border with Dubai City, was not affected by the blackout. This suggests that the Sharjah and Dubai systems are not interconnected, or if they are the interconnection is limited. What if they had been interconnected; what would have happened? There are two basic possibilities. One is that the blackout would have spilled over into Sharjah's system. The other is that the Sharjah system could have helped Dubai's system and limited the extent of the blackout. We observed here that Sharjah's system has been operating at or near capacity for several months; under these conditions Sharjah had no power to share and interconnection likely would have led to a wider blackout, not a smaller one.

I suspect there are political reasons why the Sharjah and Dubai systems are isolated from each other.

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