138kV bus diff protection

[Sn00ze]

I've seen these take the CT inputs as well as breaker a/b contact input. But i've also seen them jsut taking the CT input.

Can someone explain when do you need the breaker open/close input? and why?

 

[stevenal]

You can reconfigure your protection zones when the bus is reconfigured. Link

 

[davidbeach]

There is no inherent reason to go one way or the other. There are lots of people who have varying preferences though. Hi impedance or low? Probably low given that most high impedance relays aren't going to take a bunch of inputs. Status inputs make event analysis easier, but maybe you get all that from the position relays instead. Status inputs mean more wires and more test switches. If breaker status figures into your breaker failure scheme and your bus relay is doing breaker failure you're probably going to want to wire them in. What do your neighbors do, why? That may matter much more than what somebody else half a country or half way around the world does. What do you want to do? How much of a driver is cost?

 

[Mbrooke]

My guess would be breaker failure thats done by the bus protection. The 487B is capable to doing such. Some POCOs use the 52a contact in breaker failure protection and others do not. Ie, 52a or 50BFP will trigger a BF trip, for others 52a and 50BFP= BFT, yet for others just current is used. Each has its own advantage or disadvantage. *And* logic is more secure, but can miss certain breaker failures; while *or* logic is less secure but is best used for transformers or anywhere current may be below the 50BF pickup. There are other reasons like SCADA, MOD switching, ect, ect.


What are you doing or is being done?

 

[Sn00ze]

Hey,

thanks for the replies.

It is actually, a simple project. I am just adding a "B" bus protection so I guess i can just follow what they've done with the "A" protection I just wanted to understand why. I remember when i was first starting as a P&C designer they always said to me that you grab the status of anything you have to trip or open. But in this sub not only do they not have any of the inputs but it looks like they were taken out from the "A" protection during the last revision (judging by the revision clouds, but i can't be sure of that).

it is a GE-B30 87 bus prot (see attached)

 

[Mbrooke]

Attachment is not working for me.