VT Fuse Failure Protection

Any undervoltage relay is connected to the secondary side of the VT. To protect the VT against any secondary side shorts, secondary side Fuses are provided. But, if one or more of the secondary side fuses blows, it would be incorrectly construed by the undervoltage relay as a primary side undervoltage, (even though it is not so) - and thus would cause unwanted interruption. To avoid such a happening VT Fuse Failure Relays are provided. Such relays monitor the voltage availabilty at both the incoming and out going sides of the VT Secondary side fuses (as they are connected across the VT secondary side fuses). If the voltage is absent at both the ends, then it is viewed by the relay as a genuine undervoltage and thus the UV relay would trip. But, if there is voltage at the Incoming and andf no voltage is available at the outgoing end - which is the case, when a VT secondary fuse fails, it is viewed as a VT Fuse Failure and then this VT Fuse Failure Relay would block the operation of the UV Relay. Thus avoiding unwanted interruptions.