By Costis Stambolis
The electricity black out that occurred at 12:39 last Monday noon and brought half the country to its knees was in some ways predictable. At that time the country’s interconnected grid system was handling some 9,100 MW of power demand which was well above the schedule for power generation which had been planned a day earlier by DESMHE, the independent system operator.
This organization has the responsibility for planning and managing power distribution in the country’s interconnected system although the power generation units and the distribution network belong to the Public Power Corporation (PPC).
Last Monday, the day had started badly for both PPC and DESMHE since one major power generation unit of 300 MW in the Lavrion power complex, 80kms south east of Athens, was out of operation due to a hot water pump failure. Thus the national grid which has a total installed capacity of some 10,685 MW was operating with only 10% reserve capacity, which is considered small by international standards given the extent and complexity of the Greek system. According to electrical engineers familiar with PPC’s system the normal operational reserve capacity should not be less than 20% ,which is necessary to meet
Any sudden power surges especially during the hot summer months when there are large variations in the daily electrical loads due to the entry into the system of tens of thousands of air conditioning units.
These appear to be the immediate culprits for last Monday’s power failure since from 11:00 am until 12:39, when the black out occurred, some 400 MW of new power demand was added to the system, apparently all coming from air conditioning units being switched on due to unusually high temperatures which had hit Athens (the temperature had climbed to 39 degrees Celcius by 13:00)
The problem with the type of air conditioning units, now widely used in Greece, which are effectively air to air heat pumps, is that they require an inadvertedly high amount of reactive power. Apparently they demand as much active as reactive power. Seen on a large scale this creates a problem for the power producer and the system since at any time the grid must be ‘loaded’ with ample reactive power to meet demand from consumers which use appliances such as heart pumps or special lighting units which require large amounts of reactive power.
(A power station produces both active and reactive power and transmission cables also carry both active and reactive power) Over the last 15 years tens of thousands of new air conditioning units are installed every year with the result that PPC must add steadily an average of some 200 MW of new power capacity on an annual basis. According to a recent study by the independent energy regulator (RAE) the country will need some 500 MW of new power capacity to be added to the grid every year from now until 2010 in order to meet rising electricity demand which increases to the tune of 4.0 – 5.0 % annually.
When the power surge occurred last Monday noon the grid operator was struggling to meet rising reactive power demand in the Attica metropolitan area and since early in the morning some 1,600 MW of electrical capacity was being transferred, via the three main north south high voltage cable lines, from the power stations of northern Greece to the Athens area.
Installed electricity capacity in the south part of the country, where most of the demand occurs, is limited. Only some 1,700 MW of installed capacity is in place from three power stations around Athens (Lavrion, St. George station in Pireaus and Aliveri in Evia) At one point at 12:30 the operator, having advance information, that Lavrion No.3 unit was ready to re-enter operation, went ahead with the necessary commands but meanwhile demand had risen much faster than anticipated with the result that a secondary high voltage transmission line of 150 KV in the Lamia transmission substation became overloaded and hence failed.
Within a fraction of a second the whole system came down as one power station after another were automatically being cut off the system in order to protect themselves from damage. The whole south part of the country then went off the grid and it took more than seven hours to restore operation although the blackout in the centre of Athens lasted only one hour.
As the country, especially Athens, gets ready for the Olympic games the question arises if a similar blackout could occur during the actual games period from August 13 to the 29th. The government says that such a possibility is remote and that every measure has been taken to increase power capacity during this critical period.
Indeed some 400 MW of extra capacity will be added to the system by new units, currently under installation, while PPC has made arrangements with both Italy and Bulgaria, with which Greece has electricity connections, to import up to 700 MW extra power if necessary. On the other hand experts note that this August is very unusual compared to other summers, because Athens will have 500 MW of extra power demand to meet, on top of 300-400 MW of estimated new air conditioning units already in operation.
The extra power demand of 500 MW will come from the new all electric transportation systems (i.e tram, suburban railway, metro extensions, some 150 MW), the Olympic stadiums and other facilities (230 MW) and the large ships which will be birthed in Pireaus and vicinity and will draw electricity from PPC (some 120 MW). So an extra power load of some 800 to 900 MW will be added to the system during the Olympics.
If there is a succession of some very warm days the system will once more struggle to meet demand. Even if reserve capacity is in place, as the government claims, a problematic situation could easily arise due to lack of reactive capacity, which is not easily transportable over long distances (due to power losses) and which will be required in multiple quantities. According to the government’s contingency plans the grid operator will have prior approval to go ahead and cut off electricity in whole areas of the country so that it will have adequate spare capacity for both active and reactive power to move around in order to meet demand in the greater Athens area.
In order to avoid such unpleasant situations electricity experts say that the government must somehow channel developments in order to increase installed electricity capacity, by at least 2,500 MW over the next three years, around the Athens area where the bulk of electrical demand occurs. Failure to do that will mean that more blackouts
cannot be excluded in the near or distant future.