Measure At Frequencies Below The Rated Frequency - GE Multilin MIWII Instruction Manual

A.3 MEASURE AT FREQUENCIES BELOW THE RATED FREQUENCY (FREQUENCY TRACKING) APPENDIX A
A.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
A
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 MIWII
relay incorporates a metering capability for maximum values (not RMS) that is applied to the protection units not using I
I and I values only during this acceleration process. Once an admissible speed is reached (closed to the nominal
2 0
speed), the system will automatically switch the metering technique to the DFT. These protection units are the overcurrent
units, locked rotor and number of starts.
All protection units measure phase-by-phase and sample-by-sample using both metering techniques separately. When
the obtained values are very close to each other and steady, then the system switches to DFT.
A-4
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MIWII Directional Power Protection System
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1
GEK-113308