should be set as a phase-phase voltage in kV. To avoid oscillations of the output
START signal, a hysteresis has been included.
10.2.7.2 Time delay
The time delay for Overfrequency protection SAPTOF is a settable definite time
delay, specified by the setting tDelay.
TRIP signal issuing requires that the overfrequency condition continues for at least the
user set time delay, tReset. If the START condition, with respect to the measured
frequency ceases during this user set delay time, and is not fulfilled again within a user
defined reset time, tReset, the START output is reset, after that the defined reset time
has elapsed. It is to be noted that after leaving the hysteresis area, the START
condition must be fulfilled again and it is not sufficient for the signal to only return
back to the hysteresis area.
The total time delay consists of the set value for time delay plus
minimum operate time of the start function (80 - 90 ms).
10.2.7.3 Blocking
It is possible to block overfrequency protection SAPTOF partially or completely, by
binary input signals or by parameter settings, where:
BLOCK:
blocks all outputs
BLKTRIP: blocks the TRIP output
If the measured voltage level decreases below the setting of MinValFreqMeas in the
preprocessing function both the START and the TRIP outputs are blocked.
10.2.7.4 Design
The frequency measuring element continuously measures the frequency of the
positive sequence voltage and compares it to the setting StartFrequency. The
frequency signal is filtered to avoid transients due to switchings and faults in the
power system. The time integrator operates due to a definite delay time. The design of
overfrequency protection SAPTOF is schematically described in figure
266.
1MRK502052-UEN B Section 10
Frequency protection
551
Technical manual
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