Switchyard Protection

Background:

In a recent trends, the power stations have 200/400 KV outgoing line arranged in a one and half scheme breakers.

Meaning there are 3 breakers per two outgoing lines i.e 1.5 breaker per line.These breakers are connected on two buses,main bus-I and Bus-II.

When one of the line ( say-1) is tripped breakers 1-52CB and 2-52 CB trips.Then line is isolated i.e isolator 1-89, 1-89A,2-89A and 1-89L is opened, that side becomes dead (or known as Stub).Isolator 2-89B is not opened as line -2 OR (Transformer T/F-1) is in service.

Now the area between ( 3-52CB & T/F-1 and 2-52CB i.e Stub or dead end) is protected by "Stub" protection on 3-52CB side which gives bus overcurrent trip if the line isolator is opened and the current exceedes pre-set value.

nascon

Is it a Line feeder protection only?

How this protection is provided in one and half breaker scheme.