Watt Transducer Problem

[BearB]

I am rebuilding a 2400vac Induction Motor Starter. It all seems to work except for the Watt Transducer. I am using 2 CT's and a PT. The Watt Transducer has negative output or low positive when moving CT and PT wires around trying to troubleshoot. The CT's are bar type and bought new without any markings (polarity or X1, X2) I contacted GE and they said they did not know how that happen and sent me a FAX of the markings. The PT is A, B, C on primary and X1, X2, X3 on the secondary. The Watt Transducer is a Weschler and has the schematic on the device. I know I should have the phase and polarity correct and by static checks (ohm out connections) it looks correct. But I must be over looking something. Any help would be appreciated.

 

[oldfieldguy]

BearB--

You don't have to be alone in this. A good high voltage service company can test the CT's and determine actual polarity for you as well as give you valuable support in the entire project.

A good field service technician with one of these companies has experience in the problems you're facing.

old field guy

 

[waross]

You may be able to test the connections by connecting the CTs one at a time. If the transducer reads negative reverse the connections of that CT.
Have the zero and span of the Watts transducer been properly calibrated?
respectfully

 

[BearB]

The vendor claims the WT has been calibrated. I did this same rebuild to another starter two months ago using the same vendors WT and it worked ok,

 

[BearB]

Follow up. Today I rechecked all PT and CT wires with meter. All were landed where they should have been. I rolled the wires on both CT secondary and the Watt Transducer work. So the information that was supplied from the Vendor for the CT's that were not labled or marked was incorrect.

 

[oldfieldguy]

Yu can also do a single-phase test of the transducer with a single AC voltage and a variable current source.

Since it's a three-phase unit and you're testing with single phase, the chance is pretty good that you will have to allow for the phase relationship of your test setup being different that what the transducer would usually see, but this is not a big hurdle if all you're trying to do is verify some sort of correct operation.

If you have access to a three-phase relay test set, then you can replicate actual circuit conditions and fully verify the operation.

I typically run watt transducers through tests at different loads and power factors to verify that the things are really metering watts correctly.

I know you are aware that transducers come in many different varieties and it is not unheard of to have been sent the incorrect one for the application. I've seen more than one case of "well, the catalog numbers are different but it has the same the old one, so it should work".

old field guy