Measurement Principle - ABB Relion Technical Manual

1MRK 502 048-UUS A
10.1.7.1
Technical manual
than 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.
BLOCK
freqNotValid
Frequency Comparator
f < PUFrequency
Comparator
f > RestoreFreq
ANSI09000034 V1 EN
Figure 149: Simplified logic diagram for SAPTUF (81)
Frequency protection
BLOCK
OR
Pickup
&
PICKUP
DefiniteTimeDelay
Trip
Output
TimeDlyOperate
Logic
TRIP
TimeDlyRestore
Section 10
BLKDMAGN
PICKUP
TRIP
100 ms
RESTORE
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