Professor: Estonians might not even notice disconnecting from Russian grid

Enefit Power mast.
Enefit Power mast. Source: Ken Mürk/ERR

There is more and more talk of disconnecting Estonia from the Russian frequency band and risks this might entail in light of the tense security situation. ERR's Novaator portal asked Jako Kilter, head of power systems research at the Tallinn University of Technology, for the meaning of power grid frequency and potential issues.

Modern power grids depend on major fundamental agreements in the globalized world. Europe and many other parts of the world have decided to use the 50 hertz (Hz) frequency in alternating current grids. This means that the direction and amperage of current changes 50 times a second. "The frequency can be 60 Hz in USA and parts of Japan. Electronics designers and manufacturers need to consider the frequency in their work," the TalTech assistant professor said.

Electricity producers must do the same when running their machinery. An inversely proportional dependance means that the coils of an electricity generator need to revolve 3,000 times a minute to generate current at 50 Hz frequency.

"The nature of frequency means that those 50 Hz can be maintained when power production and consumption are balanced. Generators produce only as much power as there is demand," Kilter added. As consumption grows, the frequency starts going down and power stations need to up generation to maintain it.

It could take time to find the new balance point, while it usually only takes a few seconds. The frequency might change slightly during that time which usually does not affect the operation of electrical devices. Most can still operate when the frequency fluctuates by 1 Hz in either direction.

"When the change is greater, fuses usually step in and the device powers down," the assistant professor said. To avoid such incidents, the grid needs to sport enough backup power capacity.

Therefore, Estonia might have around 1,700 megawatts (MW) of controllable generation capacity to cover peak demand. However, if we consider regular maintenance and the chance that one or more of our oil shale power blocks might unexpectedly fail, it is not sensible to use gas turbine reserve capacity during ordinary periods, even if the price of electricity is high. "Some generators could work at half or even lower capacity to be able to quickly up generation when needed," Kilter explained.

Bigger is better

The bigger the grid, the more stable it usually is. "We can compare it to a truck and a passenger car. A slight breeze does little to affect a heavy truck while it might cause a smaller passenger vehicle to swerve.

There is also need for less local backup capacity. Consumption and demand rarely change abruptly in many places at once. This means that disconnecting the Baltics from the Russian network would require more reserve power on location. This costs money.

That is also the reason why severing energy links to other countries to bring down electricity bills in Estonia might not be the thriftiest course of action in the long run. Reserves would need to be maintained locally. "How much is needed is determined by the largest element to fall out of service. In this case, the 200-300 MW power block in Narva. Should it shut down unexpectedly, we will need to immediately replace it with as much generation to maintain the frequency."

It is also possible to use synchronous condensers to render the network more stable and inert, which all Baltic countries are currently building in anticipation of disconnecting from Russia. In Estonia's case, these are great flywheels. Energy can be stored in the rotating mass when it's available.

The condensers themselves do not generate power for consumers but can start sending power to the grid in a matter of seconds in the case of disruptions. If all goes well, power plants will be able to up their generation before the stored energy runs out. Consumers would not even notice any disturbance in this case.

Abrupt outages

Separating the Baltic and Russian grids could create such frequency problems. The risks are smaller for Kaliningrad Oblast and somewhat greater for northeastern Russia. "We are not buying electricity from Russia but the laws of physics mean some might be transferred between grids. If the lines that connect us are disconnected and the difference in frequency is minimal, we might not even notice anything," Jako Kilter explained.

The question is whether the Baltic grid will be able to handle disruptions as successfully as it has should there be a major short or changes in output. "If all goes well, it will make no difference whether we are in the Russian frequency band or not. But things might not always go well."

In the long run, we should make sure the Baltics are more closely linked to the mainland Europe system. "There are more lines between the Baltics and Russia than there are between Lithuania and Poland. The latter could not cover the whole of Baltic demand presently," Kilter pointed out.

The exact number of high-voltage lines needed is a techno-economic matter. Additional calculations need to be made to find a suitable balance point. In summary, the professor believes that risks association with disconnecting from the [Russian] grid are low. "There are some stability challenges, while there's more sunshine than anything else in store," Kilter winked.


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Editor: Marcus Turovski

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