5-134 G30 Generator Protection System GE Multilin5.6 GROUPED ELEMENTS 5 SETTINGS5Figure 5–52: PERCENT DIFFERENTIAL CALCULATIONSThe G30 percent differential element is based on a configurable dual-breakpoint / dual-slope differential restraint character-istic. The purpose of the preset characteristic is to define the differential restraint ratio for the transformer winding currentsat different loading conditions and distinguish between external and internal faults. Differential restraint ratio variationsoccur due to current unbalance between primary and secondary windings and can be caused by the following:1. Inherent CT inaccuracies.2. Onload tap changer operation: it adjusts the transformer ratio and consequently the winding currents.3. CT saturation....∑Winding 1currentwaveformWinding 2currentwaveformWinding ‘n’currentwaveformMagnitudephase angle, andzero sequencecompensation(as required)Magnitudephase angle, andzero sequencecompensation(as required)Magnitudephase angle, andzero sequencecompensation(as required)Decaying dcoffset filterDecaying dcoffset filterDecaying dcoffset filterDiscrete FourierTransformMAXDifferentialphasorDiscrete FourierTransformDiscrete FourierTransformRestraintphasor828714A1.CDR
