Placement of VTs/PTs

[mbrooke]

Is any one aware of, or sees an advantage in placing PTs within breaker bays (between the circuit breaker and disconnect) instead of on the outgoing line positions?

 

[AZElectrical]

We have bus (line) side PTs installed at our plants, which I suppose would be upstream of both the CB and disconnect in your case. This is because the bus voltage is a permissive in the start circuit associated with each motor (motor cannot start if bus voltage is too low).

 

[ATSman]

If they are part of the protection scheme then typically they are fed from the line side of the breaker.

 

[Tony S]

Horses for courses.

We used VT’s (PT’s) on the busbars for metering of the various outgoing ways and on the circuit side for incoming feeders. Being cheapskates one busbar VT would serve the metering for several outgoing ways.

 

[mbrooke]

Thanks for the replies This is a 115kv substation. Normally the VTs attach to the lightning arrestor leads, however its being considered whether or not to place them in the breaker bays.

 

[Bugman1400]

For transmission substations, there are a variety of reasons for doing it either way. Its more common to put the line PT on the line side of the disconnect because it indicates the actual state of the line regardless of the position of the disconnect or breaker. For lines that have power line carrier, the PT is typically on the line side.

I think some utilities put the PTs before the disconnect for maintenance or replacement purposes. It allows you to PM or replace the PT without dropping the line out.

 

[mbrooke]

For transmission substations, there are a variety of reasons for doing it either way. Its more common to put the line PT on the line side of the disconnect because it indicates the actual state of the line regardless of the position of the disconnect or breaker. For lines that have power line carrier, the PT is typically on the line side.

I think some utilities put the PTs before the disconnect for maintenance or replacement purposes. It allows you to PM or replace the PT without dropping the line out.

Thats the driver here, that and if the PT fails, the line can immediately be put back into service by isolating the breaker bay.

But, I want to ask, how important is it in general to know the line's condition?

 

[Bugman1400]

Thats the driver here, that and if the PT fails, the line can immediately be put back into service by isolating the breaker bay.

But, I want to ask, how important is it in general to know the line's condition?

Most substation operators and lineman will tell you that they prefer to have a local status of the line.....whether it be a panel indicator light or a panel meter. That lets them know that the line is heated up from the other end.

 

[mbrooke]

Most substation operators and lineman will tell you that they prefer to have a local status of the line.....whether it be a panel indicator light or a panel meter. That lets them know that the line is heated up from the other end.

But you could always close the disconnect with the breaker open and determine the line's condition from there? FWIW this is a main and transfer buss application so if one bay is out for service the spare bay will pick up PT, CT and breaker function for the given line.