Measurement Principle - ABB REG650 Technical Manual

1MRK 502 043-UUS B
10.1.7.1
10.1.7.2
10.1.7.3
Technical Manual
the set time delay the TRIP signal is issued. To avoid an unwanted trip due to uncertain
frequency measurement at low voltage magnitude, a voltage controlled blocking of the
function is available from the preprocessing function, that is, if the voltage is lower
than the set blocking voltage in the preprocessing function, the function is blocked and
no PICKUP or TRIP signal is issued.

Measurement principle

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. If the
voltage magnitude decreases below the setting MinValFreqMeas in the SMAI
preprocessing function, which is described in the Basic IED Functions chapter and is
set as a percentage of a global base voltage parameter, SAPTUF (81) gets blocked, and
the output BLKDMAGN is issued. All voltage settings are made in percent of the
setting of the global parameter VBase.
To avoid oscillations of the output PICKUP signal, a hysteresis has been included.
Time delay
The time delay for SAPTUF (81) is a settable definite time delay, specified by the
setting tDelay.
Trip signal issuing requires that the under frequency condition continues for at least the
user set time delay. If the PICKUP ceases during the delay time, and is not fulfilled
again within a defined reset time, the PICKUP output is reset.
When the measured frequency returns to the level corresponding to the setting
RestoreFreq, a 100ms pulse is given on the output RESTORE after a settable time
delay (tRestore).
Blocking
It is possible to block underfrequency protection SAPTUF (81) completely, by binary
input signal:
BLOCK: blocks all outputs
If the measured voltage level decreases below the setting of MinValFreqMeas in the
preprocessing function, both the PICKUP and the TRIP outputs, are blocked.
Section 10
Frequency protection
293