DOC. MIE91093 Rev. 1.34 Page 54 of 145
1.7 FREQUENCY RATE OF CHANGE RELAY TESTING
1.7.1. Introduction
This type of relay monitors the line frequency and whenever a
quick variation is detected, it operates. Normally it is used to
disconnect loads from the line and to preserve the stability of
the whole network.
The test is performed using the auxiliary voltage generator,
that allows setting the output frequency and the frequency
rate of change (ROC). We will use the pre-fault and fault
selection, so that:
. Pre-fault output is set at nominal voltage and mains
frequency;
. Fault output has the same amplitude; frequency and ROC are
modified according to our test.
Next steps depend upon the type of relay and upon the type of
test you want to perform. The following example applies to a
frequency ROC relay with:
. A frequency range, from F< to F>, within which it does not
trip;
. Absolute min and max frequencies, F<< and F>>, below and
above which it trips in time T2;
. For frequencies between F< and F<<, or between F> and
F>>, it trips with delay T1 if ROC is more than the set
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