Blocking voltage setting in under voltage protection relay 1

[Bira]

Some under voltage relays provide a blocking voltage setting as one of the relay parameters. The purpose of this setting is to block the operation of the UV relay if the voltage dropped below blocking voltage. Can anyone please provide the following clarifications.

1. What is the purpose of this setting.
2. What are the power system conditions that needs this setting.
3. what is single phase blocking, two phase blocking and 3 phase blocking voltage significance/application in power system

thanks

 

[slavag]

Hi Bira,
Very shortly.
Standard setting is 0.2Unom.
This setting avoid unwanted trips:
1. VT on the BB and main CB open, w/o thsi setting you have trip .
2. VT on the infeed cable, no voltages, continius trip to CB.
3. Fuse blown, MCB open.
Best Regards.
Slava