Reactive Power Management

Determine localized reactive power import and export capability in real time

Reactive Power is often overlooked in reliability evaluations. However, unrealistic values of localized reactive reserves can lead to reliability problems such as voltage collapse. Since reactive power cannot be transferred over long distances, it therefore must be dealt with and maintained locally.

Define Reactive Reserve Zones

To monitor and manage system reactive reserves on a regionalized basis, reactive reserve “zones” need to be identified such that stations within the same zone are electrically coherent to each other. This process is performed with data from various seasons as either an engineering service or a software tool.

Both the electrical and physical distances between the buses are considered in determining the zones, ensuring that buses within the same zone will have similar electrical properties and are physically close to each other. Utility customers seek to perform this “zone definition” practice once a quarter.


Real-time VAR Management Systems

The BSI VAR Management System (VMS) is a real-time visualization and analysis tool to monitor and maintain reactive power reserves. The VMS takes snapshots from the EMS to perform real-time evaluations for each zone, including:

  • Determining load demand and capability to meet demand
  • Detailed information on MVAR sources by generating units and capacitors
  • Capability for reactive power import from neighboring zones
  • Identifying the weakest buses and critical generators
  • Control switching suggestions to maintain adequate reactive power
    • Enhancement Control is where users can input by how much they want to increase the local reactive reserves, and the tool will find the necessary control actions to achieve this goal.

The SERC Reliability Corporation is responsible for ensuring reliable and secure electric grids across 16 states in the southeastern and central United States. SERC recommends active management of local reactive power sources and, when the audit team came across the BSI VMS implementation at Tennessee Valley Authority, their verbal feedback was that it is a “best practice solution”.