Essentials of Renewable Energy Protection and Monitoring

More and more renewable, distributed-energy resources (DERs) are connected to the bulk power system. These resources must meet certain requirements of grid support. In case of a voltage drop, these power plants are required to continue supporting the grid and not be disconnected immediately. Therefore, conventional phase-undervoltage protection is not adequate. A timed and count-qualified phase-undervoltage (27T) element keeps the DER operating to prevent grid collapse. The amount of controllable power reserves (active and inductive reactive power) from large-scale, conventional power plants is decreasing. Another concern with wide application of distributed renewable energy resources is maintaining reactive power support for grid voltage stability. Grid voltage stability is affected by faults, increasing load with large reactive power requirements, and automated changes within the network that can lead to power-system voltage drops. In severe cases, voltage instability might cause a power outage (blackout). National grid codes and regulations require that DERs feeding the grid must support the voltage during a network failure. If a voltage drops and an inductive, reactive power flow in the direction towards the DER generating unit occurs, then an undervoltage element controlled by reactive power (27Q) removes the DER from the bulk power system. Thus, more reactive power is available in the BPS, preventing voltage collapse and a possible blackout. This paper discusses the importance of reactive power and voltage support and methods to safely interface distributed energy resources to sustain the bulk power system.