Overall Generator & Transformer Differential Protection

The 889 provides overall generator and transformer differential

protection (87O). It covers the protection zones from the generator

neutral to the Generator Step-Up (GSU) Transformer’s High

Voltage (HV) winding. For mid to large-size machines, the typical

protection philosophy and architecture is to implement a dedicated

transformer protection device along with a single function

differential relay to provide the overall differential protection

between the transformer and the generator. With support for 3

sets of phase CT inputs, the 889 can replace the single function

device, providing the necessary overall differential protection

with the added benefit of protection redundancy for both the

Transformer and the Generator, when there is no tapping between

the generator and GSU or unit transformer.