On November 4, 2006, Europe suffered one of the largest disturbances in its electrical power grid of the past half century. 15 million households were disconnected from the grid for 20-40 minutes. A trivial error that should not have meant any significant disturbances cascaded and spanned much of continental Europe. This nearly threw the continent into a blackout that would have dwarfed the North American power-out in 2003. While the direct cause of the 2006 disturbance was operator error, a root cause of the problem and a significant factor in delaying getting the grids back online, was wind power and combined heat and power (CHP) plants.
The European power grid has been constructed, basically from scratch, since the end of World War II. The grid in itself is divided between a number of different Transmission System Operators (TSOs), like for instance E.ON (Germany), RTE (France) and TenneT (The Netherlands). Each country's domestic power grid is serviced by one or more TSOs. In order to provide stability and safety of the power supply TSOs are connected to each other. The basic idea was that if an area suffers a major disruption, neighbouring TSOs can help by pushing power from their grids into the affected area.
However over time things have changed. With the increased use of supposedly more environment friendly power plants, such as wind turbines and CHP plants, coupled with requirements to cut down on emissions, TSOs today are required to accept power from neighbours if the latter has a surplus of low-emission power. While this sounds good in theory as it forces TSOs to use "greener" power, instead of for instance coal power, this means that the power grid is used in a way which it was not designed for. Shunting power from one area to another puts high loads on the power transmission lines. In effect the European power grid is often operated close to maximum of what it can handle. To rectify this problem, more power lines should be built, but this is becoming increasingly more difficult and thus we are stuck with the problem.
Due to environmental reasons, the development of the transmission system is more and more affected by stricter constraints and limitations in terms of licensing procedures and construction times. The reality today is that many UCTE TSOs face significant difficulties to build new overhead lines due to long authorization procedures and regulatory regimes.
System Disturbance on 4 November 2006
union for the co-ordination of transmission of electricity
The windy weekend
November 4, 2006, was a Saturday. The event took place in the evening, starting at 22:10 CET. While power consumption is low in evenings and even more so during weekends, the load on the grid was still high. The reason for this was that TSOs use these low-periods to disconnect some power lines to perform maintenance on them. This means that remaining lines still operate at near full capacity even if demand is low.
Such conditions also meant that the fraction of intermittent and distributed power production such as wind and CHPs was higher than normal, something that was further compounded by the fact that Germany was experiencing windy conditions that evening. Large amounts of power was therefore being routed into The Netherlands and Poland, straining the power lines.
E.ON Netz was to disconnect a power line. Calculations had predicted that this should have been alright without compromising the safety of the power grid. However due to changes in the conditions - Germany's unforeseen windy weather, and a rescheduling that was communicated late to the other TSOs - the disconnect and rerouting of power overloaded the remaining lines. These power lines tripped (automatically disconnected) in order to protect them from becoming damaged. This caused more overloads in other power lines, causing further trips. This is what is know as a cascade. The cascade had within seconds divided the European power grid into three isolated "islands": west, north east and south east.
The west area, having lost the connection to eastern Germany where much power was coming from, suffered a large deficit in power production. In order to protect the power grid and equipment connected to it, TSOs started load shedding, that is to say they started disconnecting customers from the grid in order to lighten their load. For each TSO 3-20% of all customers were disconnected and suffered power outs. In total approximately 15 million European households were affected by this.
In the north east area, the problem was the opposite. With the consumers in the west disconnected, the power generators surged as there was no-one that could accept the power they produced. Windmills are particularly sensitive to this and automatically disconnected from the power grid. Within a minute the north east area stabilized.
The south east area suffered a rather small power deficit in comparison and the impact was therefore smaller.
Trying to get back online
The west area started up power generation reserves to counter the production deficit. Within fifteen minutes the west area had stabilized to nominal production, although they were still disconnected from the north east.
In the north east however the different TSO operators had big problems. This was because the windmills and CHP plants that had tripped, automatically reconnected themselves, again causing a production surplus. There was no way to keep the windmills from doing this. To counter it the TSO operators had to manually prevent overloading the grid by instructing other power plants to cut down on production or shut down completely, and engaging power buffers such as pump storage units. This was while they at the same time tried to diagnose what had happened and why they had a disturbance in the first place. There was much confusion and which meant that the north east area was delayed in getting things back to normal.
In order to help counter the production surplus from the uncontrollable windmills, the control block leader for CENTREL (TSOs in Poland, the Czeck Republic, Hungary and Slovakia) somewhat unconventionally agreed to accept much of the surplus. However this meant that huge amounts of power was suddenly being routed eastwards, overloading some power lines up to as much as 140% of normal capacity, severely risking splitting the power grid again. Luckily this did not happen.
As the power levels were restored they tried to get the different areas connected again. Starting at about 25 minutes after the problems began, they tried to resynchronize the different networks. However for another quarter hour, the networks would not connect to each-other because they were fluctuating too much or not lining up to each-other. Either they wouldn't even attempt a connection or they would trip out again after a few seconds. At 22:47 did the networks begin to connect properly, and not until over an hour later, at 23:57, were things back to normal.
Opponents of nuclear power and proponents of "green" power such as wind and CHPs often argue that nuclear power leads to poor safety and reliability of the power production. The argument is that "putting all eggs in one basket" puts us at a risk of a serious power shortage. They argue that distributed power such as wind is better because it spreads the risk.
However the events of November 4, 2006, point to the exact opposite. While the grid was always made to handle large single-point outages, such as a nuclear power plant going offline, with fairly local load balancing, it was not made to being operated the way we are forced to do with intermittent power. With wind power being essentially uncontrollable and fluctuating there is a need to shunt power long distances through power grids that were never built to handle it. This in turn puts strain on the grids, lessening the margins and risking cascading chaotic failure of an entire continent.
With increased use of wind and other intermittent power sources, this risk can only be increased unless we basically tear out our entire transmission grid and build a new one. This is an investment that will not come cheap. Those arguing for large scale power production using intermittent sources, such as wind, must seek an answer to the following question:
Is it prudent, economical, or even feasible to replace the entire power grid of a continent, just to accommodate a notoriously troublesome source of power?
/Michael Karnerfors, for Nuclear Power? Yes Please