Lightening the load

A little over two years ago, on 9 June 2005, the emirate of Dubai was left paralysed for several hours by a power blackout from around 9:45 in the morning. Disruption to mobile phone networks and chaos on the city's busy roads ensued. Lifts, computers and air conditioning units stopped working, while water supply was also lost in some areas.

"A sudden failure in one of the main transmission substations at Jebel Ali power station caused the power failure to the city of Dubai," read a statement issued by the Dubai Electricity and Water Authority (DEWA) shortly after the event.

"The emergency and maintenance teams of DEWA were immediately dispatched to attend the fault and started with immediate effect the gradual restoration of the power supply, starting with the vital power requirements to hospitals, trade centres, dry dock and other main areas within less than two and a half hours.

"A technical committee has been appointed to study the causes for this sudden failure and enhance the precautions to avoid such failures in the future," it added.

Some now suggest an ageing component was responsible for the power outage, or a protection relay was in place but set to the wrong mode. In any case, such incidents highlight the care utilities must take with a network its customers often take for granted.

Demanding issue

Of course, the strain placed on the networks of the GCC countries would not have come about were it not for the rapid growth this region is undergoing. The summer months are the most demanding of all, since this is when the two biggest power-consuming categories, air conditioning and desalination plants, are at their most active.

"The probability is always there due to the acute increase in electricity demand making many of the generation units run frequently at extreme summer conditions," says Dr Abdalla M. Al-Amiri, chairman of the Emirates Energy Award committee, which recognises best practices in energy conservation and management.

"There is also the drop in reliability of some of the ageing electricity generation units across the GCC countries, which bring about unpredicted system failure on many occasions.

"Utility companies are concerned with the reliability of their systems and I envisage that they must be on their toes in the summer to cope with the rapid increase in demand," Al-Amiri adds.

At present, the situation appears most grave in Kuwait. The ministry of electricity and water is effectively accepting that is does not have enough generation capacity to meet demand during peak periods, warning residents that pre-planned power outages lie ahead.

Waleed Ali Salman, director of electricity at the Federal Electricity and Water Authority (FEWA), believes one solution for Kuwait lies in shifting the peak load. Utilities would need to speak to their biggest consumers in order to achieve this.

"Peak time is from 12pm to 4pm, when everyone comes home and puts their air conditioning on," says Salman. "They could speak to the big industries and tell them to reduce production during the peak hours and start in the evening. Making the clients shift their load would be helpful. You have to coordinate with the client."

Powerful protection

To avoid overloading network components, it is essential to keep power generation and demand very close to equal at every second. In order to do this, as with fuses in a household system, parts of the network will automatically disconnect themselves, or ‘trip' to prevent a failure cascading to other parts of a network and potentially causing a total blackout.

Everything from transformers, to cable feeders, overhead line feeders and the busbar, a thin strip of metal which conducts electricity within a substation, should be protected with relays. Protection of a busbar, for example, will limit the impact of a fault on the entire network, tripping only those feeders necessary to clear the fault. Various algorithms can be used to learn which feeder is the problem and from where the fault is coming. In that case, only the appropriate portion would be isolated.

Salman accepts that "there are always many failures on the network, maybe daily" but believes a good protection system, interrelated to all the equipment, provides reliability. He describes it as "the brain of the network".

"The fault is always there - from old equipment, overloaded equipment, overload cables, cut cables by a contractor - it is always there but once you have a good protection system, it isolates the fault and prevents cascading and a big disruption in the network."

Load-shedding

Salman claims FEWA takes all the necessary measures to avoid any big outages, running its network very tightly and employing a 5-stage automatic underfrequency load-shedding (UFLS) system in an effort to keep generation equal to demand.

When an unexpected major supply shortfall occurs, as a result of a major generator or transmission line ‘tripping out' of service, the frequency at which the electricity is supplied starts to fall. If the frequency is allowed to fall unchecked, consumers' electrical equipment would be at risk and the electricity supply system itself could be damaged.

Underfrequency load-shedding is the disconnection of a predetermined number of consumers from the network by automatically operated devices. It therefore allows the frequency to return to its normal level, restoring the balance of supply and demand and minimising the harm and disruption to consumers.

"In case a fault occurs - say we lose one or two gas turbines and we can't cope with the demand - the grid pressure goes down, but the system automatically starts activating the appropriate stage," explains Salman. "It is already highlighted what load is to be shed, so it can be shed immediately. So we rescue the network. If it goes further, we will shed more and more."

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