Measurement Principle; Time Delay; Blocking; Design - ABB Relion 670 Series Technical Reference Manual

1MRK 505 208-UEN B
8.2.2.1
8.2.2.2
8.2.2.3
8.2.2.4
Technical reference manual

Measurement principle

The fundamental frequency of the positive sequence voltage is measured
continuously, and compared with the set value, StartFrequency. Overfrequency
protection SAPTOF is dependent on the voltage magnitude. If the voltage
magnitude decreases below the setting IntBlockLevel, SAPTOF is blocked, and the
output BLKDMAGN is issued. All voltage settings are made in percent of the
UBase, which should be set as a phase-phase voltage in kV. To avoid oscillations
of the output START signal, a hysteresis has been included.

Time delay

The time delay for Overfrequency protection SAPTOF (81) is a settable definite
time delay, specified by the setting TimeDlyOperate.
TRIP signal issuing requires that the overfrequency condition continues for at least
the user set time delay, TimeDlyReset. 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, TimeDlyReset, 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.

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 IntBlockLevel, both the
START 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 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 134.
Section 8
Frequency protection
263