Protective Elements
f< – 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, consumers, or electrical operating equipment
in general against underfrequency.
f> – 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 tripping pickup until the
tripping delay has elapsed, a tripping command will be issued.
With this setting the frequency element protects electrical generators, consumers, or electrical operating equipment
in general against overfrequency.
Working Principle f< and f>
(Please refer to the block diagram on next page.)
The frequency element supervises the three voltages (depending on if the voltage transformers are wired in Star or
Delta connection »
VL12«
, »
VL23«
und »
VL31« oder »VL1«, »VL2« und »VL3«)
. If all of the three phase voltages
are e.g. below 15% Vn, the frequency calculation is blocked (settable via parameter »
V Block f«
). According to the
frequency supervision mode set in the Device Planning (f< or f>), 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.
904 MCDGV4 DOK-HB-MCDGV4-2E
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