In an islanded microgrid system with energy storage, an electrical generator relay plays a crucial role in maintaining stability and ensuring proper operation of the microgrid. The main function of the relay is to detect and respond to various conditions and events that may occur within the microgrid to protect the system and its components. Here's how an electrical generator relay typically works in such a system:
Detection of Islanding: When the microgrid becomes disconnected from the main grid due to a power outage or other reasons, the electrical generator relay detects the islanding event. Islanding refers to the condition where a portion of the distribution system continues to operate as an independent microgrid, even though it is disconnected from the larger utility grid.
Frequency and Voltage Monitoring: The relay continuously monitors the frequency and voltage levels within the microgrid. During islanded operation, the load and generation balance might change, affecting the frequency and voltage. The relay compares these values against predetermined thresholds to ensure they stay within acceptable limits.
Protection against Overfrequency and Underfrequency: If the frequency goes beyond the predefined limits (overfrequency or underfrequency), the relay will act to control the generators. For example, in case of overfrequency, it might trigger load shedding or instruct the energy storage system (ESS) to absorb excess energy. Conversely, during underfrequency conditions, it might start additional generators or instruct the ESS to discharge and support the load.
Protection against Overvoltage and Undervoltage: Similar to frequency, the relay monitors voltage levels. In case of overvoltage, it can activate reactive power absorption from the ESS or curtail generation to reduce voltage. Conversely, during undervoltage conditions, it can instruct the ESS to supply additional power or start additional generators to boost voltage.
Synchronization and Island Reconnection: When the main grid is restored and the microgrid needs to resynchronize with it, the relay ensures that the microgrid's frequency and voltage are in sync with the main grid. Once proper synchronization is achieved, the relay permits the islanded microgrid to safely reconnect to the main grid.
Protection Coordination: In a microgrid with multiple generators and energy storage sources, the relay ensures proper coordination between different protection devices. For instance, it ensures that the protective relays of different generators do not act inappropriately against each other during transient events.
Overall, the electrical generator relay in an islanded microgrid with energy storage is essential for maintaining system stability, preventing damage to equipment, and enabling a seamless transition between islanded and grid-connected modes of operation. It acts as a safeguard to ensure the reliable and secure operation of the microgrid in various operating conditions.