3.27.2 Undervoltage Blocking and Evaluation Time
Over-/underfrequency protection requires a measuring voltage of sufficient
magnitude. Over-/underfrequency protection will be blocked instantaneously if
the measuring voltage falls below the set threshold of the undervoltage stage.
In order to avoid frequency stage starting caused by brief frequency fluctuations
or interference, the evaluation time can be set by the user. The operate
conditions must be satisfied for at least the duration of the set evaluation time in
order for a signal to be issued.
47Z0151A
f<>:
VMeas
305 725
f<>:
No. periods reached
305 701
f<>:
fMeas
305 726
f<>:
Undervolt. block. V<
[ 018 200 ]
f<>:
Evaluation time
[ 018 201 ]
f<>:
Blocked by V<
[ 042 102 ]
Fig. 3-138: Undervoltage blocking and evaluation time setting.
3.27.3 Operating Modes of Over-/Underfrequency Protection
For each stage of the over-/underfrequency protection function, the user can
choose between the following operating modes:
●
Frequency monitoring
●
Frequency monitoring combined with differential frequency gradient
monitoring (df/dt)
●
Frequency monitoring combined with mean frequency gradient monitoring
(Δf/Δt)
3.27.4 Frequency Monitoring
Depending on the setting, the P634 monitors the frequency to determine
whether it exceeds or falls below set thresholds. If an operate threshold in excess
of the set nominal frequency is set, the P634 checks to determine whether the
frequency exceeds the operate threshold. If an operate threshold below the set
nominal frequency is set, the P634 checks to determine whether the frequency
falls below the operate threshold. If it exceeds or falls below the set threshold, a
set timer stage is started. The timer stage can be blocked by way of an
appropriately configured binary signal input.
3.27.5 Frequency Monitoring Combined with Differential Frequency
Gradient Monitoring (df/dt)
In this operating mode of the over-/ underfrequency protection function, the
frequency is also checked to determine whether the set frequency gradient is
P634
3 Operation
3-186 P634/EN M/R-42-A // P634‑311‑653
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