The power network is facing a huge change moving from centralized, large generation stations to smaller, distributed generation stations and micro grids. To keep the robustness, stability and safety to the high standards we are used to will be a huge challenge. Accurate communication leading to quick and correct decisions will be key in the development of the smart grid. The relay protection in these distributed generation stations is many times rather basic but they have their challenges when it comes to testing.
To keep the voltage and frequency stable with increased numbers of small-scale distributed generation sites with uncertain capacity which cover the gap for the reduced amount of large and stable generation plants, is the major concern. This has also been recognized by IEC who released a new standard with focus of the frequency protection, IEC 60255-181:2019 Functional requirements for frequency protection.
Frequency and ROCOF
Since February 2019, there is a new relay protection standard from IEC: IEC 60255-181, specifying relay performances and test methodologies of Frequency and ROCOF
Relays. This standard have specified the mathematical formula which should better reflect potential frequency changes in the power network. Before this standard, the relay protection manufacturers made their own interpretation of how the frequency changed which lead to that the frequency protection many times reacted different to the same test. From now on it shall be same reaction among all manufacturers compliant to this new standard.
An application note describes the standard requirements on the waveform, what it means to testing, a test solution to comply with the standard, what benefits there are to test old relays to the new standard, etc. Follow this link to learn more about ROCOF and this to learn more about frequency protection in general.
Self-powered relays will be an important component for the protection of the smart grid. While they allow reducing the cost of the protection system, they are definitely a challenge for relay test sets, that are required to provide the voltage and current signals to simulate the power system fault, but also the generated signals need to have necessary electric power to supply the protection relay. The SVERKER 900 is designed to manage this task and this Technical Guide describes how two self-powered relays can be tested, details on the principles adopted in the testing with reference to relevant IEC standards and to the relay manuals. In addition, basic instructions on the correct usage of the testing possibilities offered by the SVERKER 900 are described.