Metering Algorithms - GE Multilin MIGII Instruction Manual

2 PRODUCT DESCRIPTION

2.4 METERING ALGORITHMS

2.4METERING ALGORITHMS
During generator startup, the frequency value for voltage in terminals and currents that may appear if a fault occurs in that
moment will depend of the machine speed. MIGII incorporates a metering algorithm for maximum values (not RMS) that is
not influenced by the frequency value of the measured magnitude, as it happens with other algorithms such as DFT, which
are affected by frequency. The relay calculates for each measure semi cycle the maximum or minimum value. The effective
measure is calculated as follows:
2
In order to guarantee proper operation of the protection elements, independently from the frequency, timed overcurrent
(51P/51G), undercurrent (37) and locked rotor (48) protection elements use the maximum values algorithm, while
instantaneous overcurrent (50P / 50G), thermal image, negative sequence overcurrent, number of starts, and restricted
ground differential protection elements use DFT algorithm for metering.
GEK-113188A MIGII Digital Protection for Electrical Machines 2-5