The national power system is built to function reliably, efficiently and flexibly whilst responding to fluctuating electricity consumption. Finland’s electricity quality criteria ensure that local reliability is maintained when a new power plant is connected to the grid. In addition, the Finnish power system is capable of monitoring fluctuating consumption levels continuously at a national level, even in the event of a sudden disturbance. The organization responsible for the power system, Fingrid, is also tasked with ensuring that grid transmission capacity is sufficient for transporting large amounts of locally produced energy to wherever the electricity consumption is required.
Balancing and reserve power are required to safeguard the operation of the power system. These reserves are acquired in a number of ways: Fingrid can buy the power from flexible power plants (hydroelectric, gas and coal-fired) and flexible power consumers, or rely in part on the flexible power transmission capacity with Sweden and Russia. Balancing the grid needs to work in both directions, but a sudden increase in consumption is usually more critical, i.e. more difficult and more expensive to correct than a sudden peak in generation.
Balancing and reserve power serves the entire power system, including all electricity producers. Additional investments into the power system are needed when more generation plants are built to meet increased electricity consumption. There is normally no need to indicate that any generation method particularly requires balancing power. When flexibility is added to the power system to accommodate the construction of wind power or a new traditional power station, this improves the operation of the entire system. If small amounts of new generation capacity are added or capacity is replaced by different generation methods, the power system can function without additional investments. However, when reviewing larger generation amounts it is important to examine the overall effects of changes on the power system i.e. is there enough flexibility and is system security still high?
All electricity producers and consumers connected to the grid have some effect on electricity quality. Good electricity quality means that the supply is uninterrupted, the electricity amplitude and frequency are stable, the waveform is a sine wave and the voltage level is appropriate.
In general, electricity producers raise the voltage and consumers lower the voltage. Fluctuating production from wind power causes fluctuations in grid voltage. These voltage fluctuations can be due to gust conditions, which cause relatively slow voltage fluctuations. Starting and stopping a generator can be seen as a change in the voltage level. Wind turbine generators fitted with circuit breakers cause an approximately 1 second voltage dip when the generator restarts, but the magnitude of the voltage dip can be reduced using start-up circuitry containing thyristors. In a weak grid, it is also possible to observe the regular, rapid voltage fluctuations that occur because wind turbine output is greater when blades are in the top position. Voltage level changes and fluctuations are always greatest close to the turbines and diminish towards the electricity substation.
Distribution networks are traditionally designed to transmit electricity from the substations to the consumers. When individual wind turbines or a small wind park is connected to a distribution network, it is important to ensure that the voltage stays within accepted values throughout the network and that network security functions correctly. In the event of a network fault, the wind turbine generator disconnects from the network automatically and stops production, so that it does not hinder the interruption of arc faults or continue electrification of an isolated part of the network, which would endanger returning the network to a normal state.
Transmission of electricity causes power losses proportional to the root mean square of the current. When wind turbines are located near consumers, less transmission is required and therefore power losses decrease. For this reason some Finnish grid operators have negative energy costs for electricity generation on weekdays or even for generation at any day or time. A negative energy cost means that the grid operator pays the wind power producer.