1-phase bus differential relay using auxiliary summation CT's
In gas insulated switchgears the current transformer cores in the bushings can preferably be used. The total gas insulated switchgear will then be included in the measuring zone of the bus protection.
Intermediate summation current transformers are used for adjustment of the CT-ratios and to reduce the secondary current. They are also used to galvanically separate the primary from the measuring circuit of the relay.