Theory Of Operation; Ct Saturation Detection - GE G30 Instruction Manual

G30 Generator Protection System
Chapter 10: Theory of operation

Theory of operation

This chapter outlines advanced information on operation.
10.1 Saturation detector

10.1.1 CT saturation detection

The saturation detector of the G30 takes advantage of the fact that any CT operates correctly for a short period of time,
even under very large primary currents that would subsequently cause a very deep saturation. As a result, in the case of
an external fault, the differential current stays very low during the initial period of linear operation of the CTs while the
restraining signal develops rapidly. Once one or more CTs saturate, the differential current increases. The restraining signal,
however, yields by at least a few milliseconds. During internal faults, both the differential and restraining currents develop
simultaneously. This creates characteristic patterns for the differential - restraining trajectory, as shown.
Figure 10-1: CT saturation detection internal and external fault patterns
G30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 10-1