Theory Of Operation - GE G60 Instruction Manual

G60 Generator Protection System
Chapter 10: Theory of operation

Theory of operation

This chapter outlines advanced information on operation.
10.1 Phase distance through power transformers
As a Wye-Delta transformer introduces discontinuity for the zero-sequence circuit, the ground distance protection cannot
be applied, except special circumstances, to respond to faults behind the transformer.
The phase distance elements, however, can be developed so that both accurate reach and correct fault phase
identification is retained for faults behind the power transformer as seen from the relaying point. Without appropriate
compensation, the reach of the relay depends on a type of fault, creating considerable difficulties in applying the relay.
The G60 provides for any location of the VTs and CTs with respect to the involved power transformer and the direction of
any given zone.
In the following equations, the VT and CT locations are referenced as "None" if the transformer is not present between the
CT/VT and the intended reach point. Otherwise, the location is to be selected as a type of a transformer as seen from the
VT/CT position towards the intended reach point. The following figure explains the adopted rules.
G60 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 10-1