Under Voltage Protection

[Arba]

Anybody can tell me if I set to block the under voltage protection on a main 5 KV BUS, when one of the relay PT fuses would blows (The 27 Relay has the feature to supervise the PT voltage), with the excuse that probability of two events: under voltage phenomena and PT Relay Disruption happening in the same time would be very slim. At the end I can eliminate the main breaker trip when a PT fuse is blown, by just alerting the personnel to replace the fuse in a better time.

 

[slavag]

Hi.
Yep, its standard fro lot of protection functions are used undervoltage detector, like to : 27, 21, 67, etc...

You block undervolatege function by fuse failare supervision/monitor, possible block undervoltage function by undervoltage block level, about 0.2Un, less 27 will blocked.
Best Regards.
Slava

 

[SMB1]

Hi,

usually 27 relay operates with time delay to avoide any operation during loss of PT or transient voltage dip.

to detect loss of PT, FFR fuse failure relay (98) is installed. this relay compare two voltages from two PT secondary windings.

if your 27 relay is numerical there is a feature to do so, however, it could not detect the three phase PT failure.

I do recommend to use stand alone relay for this function.

thanx
smb