ABSTRACT
The best protection technique now and for more than 50 years is that known
as differential protection. Here the electrical quantities entering and leaving
the protected zone or area are compared by current transformers (CTs). If the
net between all the various circuits is zero, it is assumed that no fault or
intolerable problem exists. However, if the net is not zero, an internal problem
exists and the difference current can operate the associated relays. In general,
internal faults provide significant operating current, even for fairly light
faults.
