PT Fuse Failure Relay Working Principle VTFF:
PT Fuse Failure Relay VTFF is used to sense the PT fuses healthiness. Generally, In high voltage power system all the voltage reference will be taken from the potential transformer. To protect the potential transformer against secondary short circuit over load, the fuse is installed in primary side of the potential transformer. At that same time the PT secondary is connected through a MCB to avoid frequent PT fuse failure. However, the PT fuse failure relay sense the output voltage of the potential transformer for that, the reference voltage is taken from the secondary output of the MCB.
First configuration 1 (Medium voltage) PT Fuse Failure Relay :
Under voltage takes the voltage reference from the secondary of the PT. Under voltage relay should trip or operate only at that time of both primary and secondary supply failure. Here, the under voltage relays are connected across the two potential transformer which means phase to phase, but PT fuse failure relay is connected in a single potential transformer which means phase to ground. Therefore, upon failure of single fuse phase, the relay gives necessary annunciation on your annunciator panel.
Note: The Under voltage only operates when the voltage falls be 90% (as per setting).
Configuration 2 Low voltage configuration:
This is very simple method that, the relay sense the voltage across the fuse element. Since the voltage across the fuse reach high the relay operates. Under Normal condition, the voltage across the fuse is equal to zero. At the same time, The voltage across the fuse will be reach high, only when the fuse is failured.
Configuration 3 high voltage configuration:
Normally, In high voltage application, the PT primary is connected with the fuse. Since they use mcb to avoid PT overload. Here the same configuration 2 concept is used to sense the PT fuse.
PT Fuse Failured relay ANSI code: VTFF
- VTFF relay acted
- Low forward power annunciation
- Fluctuation in the MW output at the TCP Panel, when the Metering PT Fuse failured.
- 86M relay opted when the protection PT fuse failured
- Fluctuation in the MW output at the TCP Panel. The other protection relay operation is purely depending upon the Type of PT fuse failured either metering PT or Protection PT.