fuse failure supervision relay - 98

[bejoyengineer]

How and for what purpose does a fuse failure supervision relay work. as the name suggests - it's understood that it checks the status of the fuse but i have noticed that both the measureing and reference voltages are taken form the same primary source. . so which part of the circuit does it try protecting. any good links to get a good idea of this supervision relay. thanks in advance

 

[sii]

We use them in industrial applications to send a signal to a PLC. One example is on arm drives on a rotational molding machine. If a motor fails, it can be a costly event if no one notices immediately. It provides a quick and easy way to tell the PLC and sound an alarm buzzer instantly when the drive has stopped. It also allows ease of troubleshooting for the operators as well as us as maintenance personnel.

 

[bejoyengineer]

fuse failure supervision relay

fuse failure supervision relay

thanks for the answer but the relay that i was talking about is used in substation. it is connected from the Voltage transformer and there r two voltages taken from the secondary side of the VT - one is the reference voltage and the other is the measuring voltage.this relay blocks the distance relay from operating incase a fuse blows off. but the only doubt that i have is which part of the circuit does it protect.so i really don't understand the connection between a failed motor and the fuse relay

 

[richxtlc]

thanks for the answer but the relay that i was talking about is used in substation. it is connected from the Voltage transformer and there r two voltages taken from the secondary side of the VT - one is the reference voltage and the other is the measuring voltage.this relay blocks the distance relay from operating incase a fuse blows off. but the only doubt that i have is which part of the circuit does it protect.so i really don't understand the connection between a failed motor and the fuse relay

In a distance relay the potential also acts as a restraining voltage and holds the contact in the open position, if the potential fails the contact can close on vibration alone causing a unintended trip.

 

[rcwilson]

A distance relay trips if the measured impedance of the circuit is less than the trip setting. Z=V/I. If a fuse blows, V=0, so the relay measures 0 ohms; the same impedance it would see for a bolted fault on the breaker terminals. The fuse failure relay prevents false trips, but it still has to let the distance relay work for an actual fault when the voltage is very low.

Some fuse failure relays compare voltages from two VT's on the same bus on the assumption that the same event won't blow both VT's fuses.

Many digitial relays detect fuse or VT failure by monitoring negative sequence voltages and currents. If it sees negative sequence voltaes but no negative sequence currents, it must be a fuse failure.

Another application is on generator voltage regulators to prevent overvoltage when the regulators sensing voltgage goes away. (Imagine unplugging the speed signal from your cruise control set at 70 MPH.) The fuse failure relay trips the AVR or puts it in manual mode.

 

[mayanees]

i really don't understand the connection between a failed motor and the fuse relay

Sii was likely referring to fuse-loss detection for the purpose of phase-loss protection for a 3 phase motor. If left undetected, it could do damage to the motor or to some VFDs.
It's also done at a typical medium to high voltage facility service entrance point for the same reason - phase-loss protection, using the methods described by Bob Wilson in his post.
John M

 

[bejoyengineer]

Fuse failure

Fuse failure

Thanks a lot for the answer.
now i have understood on what basis it works