Time-over/underfrequency relay and protection assemblies
Frequency relays are used whenever deviations from nominal system frequency need to be detected. Underfrequency based load shedding in power systems is one common application. The RXFK 2H is suitable for load shedding based on accurate measurements and high resolution. 25 mHz or 10 mHz resolution is available for the two models. The model having 25 mHz resolution can also use the second stage measurement in the dF/dt mode.
An adaptive algorithm is used to secure operation depending on rate-of-change of frequency. This function may be supervised by the other frequency step for providing a non-delayed trip function. This may be advantageous for saving critical in-plant generation upon power system disturbances.
Underfrequency relays should be considered for applications where the detection of underspeed conditions for synchronous motors and condensors is required.
The overfrequency relay function is generally utilised for the protection of ac machines from possible damage due to overspeed conditions.