PT / CPT SWAP

[wirepuller]

Can a PT be used as a CPT? . Iam working on a 42000 volt HV contactor that the cpt is missing.A person said why not use a PT ,We have some 42000 volt 750 VA , 35: 1 ratio.
I thought PTS were used for metering only.

 

[jraef]

PTs are designed to optimize accuracy, not capacity.
CPTs are designed to optimize capacity, not necessarily accuracy.
The ratio may be the same, but the capacity is not. The PT is not meant to have much of a load on it. If you have specs, see if they match what your load requirements are.

 

[waross]

We have some 42000 volt 750 VA

You should be safe as long as the loading does not exceed 750 VA.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

Hi wirepuller
Usually PT does not supply control circuitry as you already said.
If the contactor is located in an enclosure with other breakers or contactors you may use the local control source as more reliable [provided with reserve supply source] rather than PT.
Control power transformer usually is built for 5-15 KVA .But if you don't need more than 750 VA[ depends on the current required by the control coil of the contactor] it is possible to use PT .The problem is if the 42 KV will fail no control supply source for the contactor will be available.
I think as the PT is built specially for measurement an accuracy class of 3[or more] would be better. For CPT you could see:

http://library.abb.com/global/scot/...8b05dde0d85256d9c005dbc70/$File/CPT_Flyer.pdf

Best Regards