4160/115/230 VAC Control Transformer Failure and Motor trip

[adityalagudu]

We have the following CPT installed for our motor circuit controls;

Primary 4160 VAC
Secondary 115/230 VAC
3KVA, 60HZ, K-Factor 1
3A fuse on primary, 20A fuse on Secondary

We installed these CPTs a few months back in 4 of our motor feeder units.

We had trip incidents on all 4 motors and didn't have any event report on the relay. We thought to test these transformers and measured winding resistance and turns ratio. Turns ratio comes as 41.54, 26.22, 27.44, etc, and winding resistance as 277 ohms, 11.1Kilo Ohms, 53.2 Kilo Ohms, etc. So these values are consistent.

We are trying to understand what makes these transformers fail and questioning their integrity? As these transformers are tested well in the factory. How we can eliminate this issue moving forward?

 

[waross]

Something to check.
I once encountered a lot of dual voltage ballasts with a factory mistake in the connections to the terminal strip.
The normal order of leads on a terminal strip is X4, X2, X3, X1. For low voltage, jumpers are used between X4 and X2, and between X3 and X1. For high voltage one jumper is used between X2 and X3.
If the leads to X3 and X2 are interchanged at the factory, the transformer will work and test as expected.
However when the jumpers are changed to the low voltage position as per the nameplate information, Both 115V windings will be short circuited. Burnout will be almost instantaneous.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[adityalagudu]

Waross,

Thank you for your input.

We are using secondary voltage as 115V for our applications. SO there is a jumper between X2 and X4; X1 and X3. Our circuit is connected to terminals X1 and X4. So I think the connections are good. See the attached for reference.

There is another aspect we are looking into which is K-Factor. These transformers have K-Factor as 1, which is more susceptible to harmonics and poor power quality. Is this something we can change?

 

[waross]

In the case that I cited, the numbers were on the terminal strip, not on the wires. two wires were crossed when the transformer was built.
This was determined by visual inspection. There wasn't enough left to check continuity.
There are not many harmonics in a motor control circuit, compared to the loads that do need consideration of harmonics.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

I had a 10KVA transformer with about 5 factory mislabeled leads. Happens too frequently.

Keith Cress
kcress -

http://www.flaminsystems.com