This FAQ has been written for NEAL (North East Africa and Levant) region. If you are looking for information for another region, please select the correct country from the top-left dropdown in the page and 'Navigate to Browse FAQs' in the Support menu.
What is the definition of ANSI 81R - Rate of change of frequency?
Protection function used for fast disconnection of a generator or load shedding
control. Based on the calculation of the frequency variation, it is insensitive to
transient voltage disturbances and therefore more stable than a phase-shift
protection function.
Disconnection
In installations with autonomous production means connected to a utility, the “rate of
change of frequency” protection function is used to detect loss of the main system in
view of opening the incoming circuit breaker to:
The “rate of change of frequency” protection function is used for load shedding in
combination with the underfrequency protection to:
control. Based on the calculation of the frequency variation, it is insensitive to
transient voltage disturbances and therefore more stable than a phase-shift
protection function.
Disconnection
In installations with autonomous production means connected to a utility, the “rate of
change of frequency” protection function is used to detect loss of the main system in
view of opening the incoming circuit breaker to:
- protect the generators from a reconnection without checking synchronization
- avoid supplying loads outside the installation.
The “rate of change of frequency” protection function is used for load shedding in
combination with the underfrequency protection to:
- either accelerate shedding in the event of a large overload
- or inhibit shedding following a sudden drop in frequency due to a problem that should not be solved by shedding.
Released for: Schneider Electric Egypt and North East Africa
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