Alarms
30
5.5.7.2
EXAMPLE OF ROCOF (FREQUENCY RISE UPON A MAINS FAILURE)
In this example, the generator is in parallel with the mains supply, in fixed export supplying all the
requirements of the load and exporting the remaining power to the mains supply.
Upon the mains failure event, the frequency of the generator increases due to load being removed.
This is measured over the configured number of cycles to give a Rate Of Change Of Frequency
(Hz/s). If this value remains above the configured trip point for longer than the configured delay time,
a R.O.C.O.F. trip is generated.
Generator output frequency rises and
recovers upon mains failure when in
parallel as the generator load increases.
R.O.C.O.F. (df/dt)
Rate of Change Of Frequency (Hz/s)
Time
Frequency
Hz
s
Time of mains failure
event
