GE Multilin MIB - Measure at Frequencies below the Rated Frequency

C-4 MIB High Impedance Bus Differntial Relay GEK-106426A
C.3 MEASURE AT FREQUENCIES BELOW THE RATED FREQUENCY (FREQUENCY TRACKING) APPENDIX C
C
C.3MEASURE AT FREQUENCIES BELOW THE RATED FREQUENCY (FREQUENCY TRACKING)
As already mentioned, the digital filter is related to the fundamental frequency, so higher multiple frequency values are
annulled
During the start-up of generators, the voltage frequency in terminals and currents that can appear in the event of a fault,
will depend on the machine speed. During the start-up process, the machine will rotate at very low speed, and therefore,
the obtained DFT measure will be affected, as it works on values that are related to the fundamental frequency.
In order to guarantee the correct operation of the protection units during this transitory process of acceleration, the MIB
relay incorporates a metering capability for maximum values (not RMS) that is applied to the protection units not using I
1
,
I
2
and I
0
values only during this acceleration process. Therefore, protection units 51P/51G, 48 and 37 operate using the
maximum values algorithm, while protection units 50P/50G, 49, 46, 66 y 87R operate using the DFT algorithm.