EDR-5000
IM02602007E
81U – Underfrequency
This protection element provides a pickup threshold and a tripping delay. If the frequency falls below the set pickup
threshold, an alarm will be issued instantaneously. If the frequency remains under the set pickup threshold until the
tripping delay has elapsed, a tripping command will be issued.
With this setting, the frequency element protects electrical generators, loads, or electrical operating equipment in
general against underfrequency.
81O – Overfrequency
This protection element provides a pickup threshold and a tripping delay. If the frequency exceeds the set pickup
threshold, an alarm will be issued instantaneously. If the frequency remains above the set pickup threshold until the
tripping delay has elapsed, a tripping command will be issued.
With this setting, the frequency element protects electrical generators, loads, or electrical operating equipment in
general against overfrequency.
Working Principle
(Please refer to the block diagram on next page.)
The frequency element supervises the three phase voltages »
VA«, »VB« and »VC«. If all of the three phase voltages
are below 15% Vn, the frequency calculation is blocked. According to the frequency supervision mode set in the
Device Planning (81U or 81O), the evaluated phase voltages are compared to the set pickup threshold for over- or
under-frequency.
If in any of the phases, the frequency exceeds or falls below the set pickup threshold and if there are
no blocking commands for the frequency element, an alarm is issued instantaneously and the tripping delay timer is
started. When the frequency still exceeds or is below the set pickup threshold after the tripping delay timer has
elapsed, a tripping command will be issued.
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