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The residual overvoltage relay SPAU 110 C is a secondary relay which is to be connected to the voltage transformers of the protected object. When a fault occurs, the residual overvoltage relay can be used for tripping a circuit breaker or for signalling an earth-fault only, as required by the protection application.
When the energizing voltage exceeds the set start value of the low-set voltage stage U0>, the residual overvoltage relay starts. After the set operate time t> the low-set stage operates, if the fault still persists. The high-set voltage stage operates in the same way. When the measured voltage exceeds the set start value U0>>, the high-set stage starts, and after the set time t>> the high-set stage operates, if the fault still persists.
Start information from the residual overvoltage relay is obtained as a contact function, which further can be used for controlling other cooperating protection relays, e.g. neutral current measuring earth fault relays.
The relay contains one optically isolated logic input to be controlled by an external control voltage. In the residual overvoltage relay the control input is used as a blocking input.