Due to the renewal of the grid code specifications required for power generating plants in 2018, all plants connected to the Finnish main grid that are over 0.8 kW must include features for controlling the turbine in power grid disturbance situations.
The turbine governor, i.e., the regulation and control system of a hydropower plant turbine, has several functions. Primarily, it adjusts the guide vane and runner to achieve the desired process value, which ensures that the requested power is achieved. When the frequency support feature is on, the system controls the power of the plant as the mains frequency changes. In addition, the system monitors the operation of the plant’s mechanical regulation devices, and controls and limits the operating point of the hydropower plant via the given parameter tables whenever the water surface changes.
Due to the renewal of the grid code specifications required for power generating plants in 2018, all plants connected to the Finnish main grid that are over 0.8 kW must include features for controlling the turbine in power grid disturbance situations. The grid code requirements also specify the performance, measurement accuracy, functions, registration and communication required from the plant and its control system according to the power plant class.
The purpose of the requirements is to ensure the operation of all units connected to the main grid in disturbance situations so that the disturbance is managed, and not worsened. The requirements related to the characteristics of the equipment and systems are also likely to be based on the fact that plants connected to the grid will be built to meet a certain standard and thus ensure solid operation in the grid.
In recent years, Finland’s transmission system operator, Fingrid, has also reduced the unit power limit required to participate in the production of the frequency reserve. This will allow many hydropower plants, which were previously only involved in energy production, to participate in the frequency regulation market as well. A plant that also fulfils the requirements to participate in the frequency regulation market will bring added economic value in the form of reserve production compensation in addition to energy compensation alone.
”The need for such regulation features is increasing with the expansion of renewable energy sources, so it’s logical that plants are already upgraded with controllers capable of frequency support,” says Jukka Kelloniemi from VEO’s hydropower automation team.
VEO has invested in system features and usability in the development work made to fulfil the new requirements.
“Today, all hydropower automation projects where we renew the turbine regulation and control system will include a system with a frequency support ability, in accordance with the new grid code regulations,” says Kelloniemi.
When a plant participates in the frequency reserve market, the reserve supplier must ensure that the plant’s supply and control equipment also meet the agreed regulation features between the control tests performed for the transmission system operator. Therefore, the checking of regulation features must be made easy.
“To ensure that things run smoothly, VEO has now made several improvements that take into account the wishes of the users. One target for development in our system has been the user interface, which now includes parameters to control the operation of the turbine governor and the operating points of the turbine. The user interface makes it easy to check and adjust the operation of the system.”
In the hydropower market, energy and frequency reserves are traded separately. In addition, regarding the turbine governor, the frequency reserve is further divided into containment reserve, disturbance reserve and so-called automatic Frequency Restoration Reserve (aFRR). Therefore, the owner of the machinery must also be able to switch off the product and direction of control that is not traded and to limit the amount and direction of control allowed for aFRR.
“The control speed of aFRR is the speed set by the transmission system operator and the grid code defines the power regulation speed at which the hydropower plant must be able to function. However, the speed at which the normal power setpoint is executed is a matter for the users to decide, so it’s useful for them to be able to adjust it due to seasonal variation, for example. During the formation of the ice cap, the flow through the machine is allowed to change slightly more steadily than at other times. In addition, in a situation where a spare part has to be replaced, the user interface can be used to calibrate the sensors controlling the system. This increases the usability of the system and speeds up the recovery from the disturbance situation considerably. These numerous features have been taken into account in the design of VEO’s turbine regulation and control system,” says Kelloniemi.
The guiding idea of VEO’s design is that when the system is made as easy to use as possible, the required testing and maintenance measures are also performed regularly and in accordance with the requirements.
“This increases the safety and service life of the system and reduces overall costs during the system’s lifecycle. VEO’s strengths are found in the company’s long experience in this area, knowledgeable professionals and in-house product development, which allows the system to be modified according to the specific needs of a project and to be updated whenever needed. For example, the renewal of hydraulics or components should not mean that the entire system has to be renewed,” Kelloniemi points out.
Although many improvements have already been made, further development of the system is ongoing at VEO. Further improvements are being planned, among other things, regarding information availability and how to solve both the mechanical wear on the hydropower plant caused by the frequency control and the resultant increasing maintenance costs.
“We have launched a development project at VEO to find a solution to reduce mechanical wear without having to compromise on the amount of reserve produced. If successful, the improvement will bring customers direct savings in maintenance costs and increase the operational reliability of the plant.”