SIL-D relay is designed to protect MV systems with isolated neutral. In switchgears with isolated neutral, the earth fault calculation cannot be done as an exact value due to it is not dependent from the short circuit power. It depends on the MV system capacitor it is connecting to. For this reason, the earth fault is related with the network voltage and with the features of the lines connected to the mentioned system.
Apart from the phase and neutral instantaneous overcurrent, and protection against phase inverse time overcurrent, the relay provides directional neutral overcurrent and directional isolated neutral overcurrent as well as circuit breaker failure supervision, neutral overvoltage and trip block for switch disconnector.
A recloser is fitted. This automated control shall permit closure (up to five attempts) with the possibility of programming each reclosing time
Further functions have been included, such as the cold load pickup, or the trip circuit supervision.
Main Applications: Distribution and transformation substations. RMUs and SF6 insulated Switchgears.