Blackout to be repeated?
The blackout that occurred at 12.40 p.m. yesterday, putting the Public Power Corporation’s (PPC) electricity grid south of Lamia out of commission, was something to be expected, as we have said in earlier articles in Kathimerini. The manner in which the blackout occurred was also expected. Initially, there was a drop in voltage at the 150,000-volt line at the high tension node in Lamia, resulting in the line going out of commission in order to guard against low-voltage electricity. Subsequently, all very high voltage lines from Lamia to Attica ceased to operate, resulting in the blackout. According to technical experts, who know very well how the power distribution system functions, the initial drop in voltage was due to an inability to respond to the system’s demand for reactive power. The surge in demand was due to the switching on of many air-conditioning systems which kept increasing the burden on the grid from early morning on a particularly hot day, with temperatures in the center of Athens rising to 38 degrees Celsius. It is known that air-conditioning systems demand as much reactive power as they do «real» power. Most electrical appliances (stoves, lamps, PCs) usually demand a lot of real power and a small amount of reactive power. Air-conditioning systems, which are essentially heat-absorption ducts, demand a lot of reactive power. We should note here that a power transmission line both produces and consumes reactive power. The reactive power produced is related to the grid’s apparent resistance, while the reactive power consumed is proportional to the reactive portion of the electricity squared. Thus, when our air-conditioning systems tried to absorb reactive power yesterday, the system was losing reactive power squared. Yesterday started badly, in any case, with a 300-Megawatt (MW) production unit in Lavrion, southeast of Athens, having shut down the previous night for maintenance on the hot water supply pump. At some point around 12.30 p.m., total demand was 8,910 MW, while the grid’s capacity was 10,350 MW. Between 12.30 and 12.40 p.m., there was an additional demand of 300 MW caused solely by air-conditioning systems. And, while the grid could, in theory, cover the required real power, it could not cover the extra 300 MVAR (Megavar, a Var being the unit by which we measure reactive power) that these systems demanded. Now, one of the characteristics of reactive power is that it is very difficult to transport. If a region is in sudden need of reactive power, then the grid must have available somewhere else at least eight times as much reactive power, because the power fritters away along the way. There was no way northern Greece, for example, could supply these 2400 MVAR. This would require shutting down electricity in western and northern Greece and, had something of the sort been decided, would have taken quite a long time to transfer the power needed. Indeed, in order to ensure that the rest of the country continued to have a power supply, the system switched off the lights in southern Greece for a fraction of a second. The lack of available reactive power is due to the power grid’s weaknesses, chief of which is the lack of sufficient power available in or near Attica. According to international practice, the available power generated near Athens should have been between 3,000 and 4,000 MW and not the 1,800 actually in existence. PPC is going to add a 400-MW natural gas unit next year, but it is estimated that additional demand from air-conditioning systems, the tramway, the suburban railway, new hotels and other sources will equal the power generated by this new unit. In 2006, two new thermal power units, with a total power of 700 MW, operated by the private sector, will also be added to the Attica grid. By that time, demand will have risen by another 500 MW. For this reason, we must install units producing at least 2,500 MW over the next three years near Athens. This is the only way to address the imbalance in the country’s power system, according to expert technicians. The same people say that what happened yesterday cannot be dismissed as an isolated incident and worry enormously about the possibility of blackouts during the Olympic Games, scheduled for August 13-29. In any case, a study on the role of reactive power and how to avoid shortages is lacking. Other things missing include a sufficient quantity of condensers which help to avoid sudden power surges, as well as the complete lack lack of units producing reactive power. While the problems associated with reactive power have been known over the past few years, the previous government did nothing to tackle them, while the present government seems unable to understand the nature of the problem and sheepishly follows the advice of «experts,» including the PPC, and their assurances that there is plenty of power available. But the question is not one of available power but of the quality of that power and the specific needs of the system at any given moment.
