Admittance relay

A field failure relay (40) is usually an admittance relay wifh an offset admittance zone. The tripping zone is usually determined from a circle. The relay receives a current signal and a voltage signal from the stator terminals. The impedance circle of the generator is determined and located by the following features. 

Figure 12.8 Loss of excitation characteristic of an admittance relay. The diagram is drawn in the impedance domain.

The type of feeder cables described in this section are those between switchboards within an oil industry site, rather than those between a utility power plant and an oil industry site. These feeders may be described as primary feeders as opposed to secondary feeders downstream in the system. Feeders from a utility power plant or a transmission network have protective relaying systems that are more sophisticated than those described herein, e.g. multi-zone distance protection, admittance relays, carrier protection schemes. 

Distance relay is a device that functions when the circuit admittance or impedance... 

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