Emergency active-power balancing scheme for load frequency control

The electric-power system (EPS) was developed with a purpose of transmitting the electricity from the generating facilities to consumers. One of its key operational processes is a continuous balancing of generated and consumed powers. Up to a certain active-power imbalance, frequency control is sufficient for assuring EPS frequency stability. However, in less frequent situations, additional measures are required to prevent a long lasting blackout. One of such specialized techniques is referred to in this chapter as emergency active-power balancing (EAPB). It requires a coordinated operation of numerous frequency relays installed in a wide-spread medium voltage network. This enlightens its parametrization, installation and testing complexity and at the same time stresses the need for close cooperation between transmission and distribution system operators. Even though in the past, EAPB was seldom activated, it is reasonable to expect that this will change in the (near) future. Namely, the replacement of synchronously connected generation with rotating masses by converter-interfaced generation significantly affects EAPB operation, making it one of most up-to-date research topics in the area of power engineering. In this chapter, we will first provide the theoretical background of EPS response to active-power imbalance. It is essential to understand this for fully grasping the complexity of developing an efficient and robust EAPB, which will be discussed in continuation. Depending on the developing trends of modern EPSs, challenges and recommendations for the future will be indicated at the end.