ABB Relion 670 Series Technical Reference Manual page 565

1MRK505222-UUS C
9.2.2.3
9.2.2.4
Technical reference manual
TRIP signal issuing requires that the overfrequency condition continues for at least the
user set time delay, TimeDlyReset. If the PICKUP 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, TimeDlyReset, the PICKUP output is reset, after that
the defined reset time has elapsed. It is to be noted that after leaving the hysteresis area,
the PICKUP condition must be fulfilled again and it is not sufficient for the signal to
only return back to the hysteresis area.
Blocking
It is possible to block overfrequency protection SAPTOF (81) 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 IntBlockLevel, both the
PICKUP and the TRIP outputs, are blocked.
Design
The frequency measuring element continuously measures the frequency of the positive
sequence voltage and compares it to the setting PUFrequency. 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 (81) is schematically described in figure 284.
Section 9
Frequency protection
559