67 and 67N relays

[bejoyengineer]

Just a silly question but just to make my curious mind bac to normal - Why was not 67 and 67N
relays built into a single relay as i have noticed that the R,Y,B CT wiring end up into the 67 relay
while the common of the R,Y,B CT wiring end up into the 67N relay. Then it was better if a single relay was manufactured
just like the distance relay (21). Another question i would like to ask is - how do we know where the 67 and 67 N
relay has to be placed.why is it not placed at the transformer bay? In the substaion that i am working -i have noticed that it is placed between a breaker and
a common double bus bar and this line bay is connected to another substation at a remote place which is furthur connected to a load.


B
U
S___________CT for 67 and 67N_________Breaker____________ remot s/s.
B
A
R

 

[richxtlc]

Just a silly question but just to make my curious mind bac to normal - Why was not 67 and 67N
relays built into a single relay as i have noticed that the R,Y,B CT wiring end up into the 67 relay
while the common of the R,Y,B CT wiring end up into the 67N relay. Then it was better if a single relay was manufactured
just like the distance relay (21). Another question i would like to ask is - how do we know where the 67 and 67 N
relay has to be placed.why is it not placed at the transformer bay? In the substaion that i am working -i have noticed that it is placed between a breaker and
a common double bus bar and this line bay is connected to another substation at a remote place which is furthur connected to a load.


B
U
S___________CT for 67 and 67N_________Breaker____________ remot s/s.
B
A
R

Here's a diagram from Basler Relays. Both the 67 and 67N relays can be part of a multifunction relay or individual electromechanical relays.

 

[bejoyengineer]

CT for 67 and 67N

CT for 67 and 67N

So i have understood that it can be built as a single relay but another question i would like to ask is - how do we know where the 67 and 67 N
relay has to be placed.why is it not placed at the transformer bay? In the substaion that i am working -i have noticed that it is placed between a breaker and a common double bus bar and this line bay is connected to another substation at a remote place which is furthur connected to a load. Down i am just showing how the line diagram would be.


B
U
S____CT for 67 and 67N_____Circuit Breaker_______ remot s/s---load.
B
A
R

 

[richxtlc]

The current transformer is placed as shown in my previously attached drawing. It detects changes in direction of current when the circuit breaker is closed. it is designed to prevent current from flowing back to the source where you have more than one source feeding the bus to minimize circulating current between the two stations. It will also open the secondary circuit breaker in the event of a phase-to-phase fault on the primary or a phase-to-ground fault on the secondary.