CT/PT Problems

Ragotham,

You can start with a few of the links on this page.

If you find nothing useful on those links try working the problem backwards.

You have had no CT/PT failures over the last thee years.

You have had multiple CT/PT failures over the past two months.

Something has obviously changed.

A good place to start your investigation would be:

The first time that the CT and/or PT was changed, was the correct replacement CT/PT used?

Were the conductors re-landed on the correct terminals?

Are the connections clean and tight?

Have you checked the wiring harness for breaks or shorts between the CT/PT's and the display(s)?

Is there a selector switch controlling how the display shows the CT/PT status? If so, check between corresponding terminals for continuity when closed/open and check tightness of conductor terminations.

Is there anything in the circuit that would cause an intermittent open across any CT/PT?

Check back with us and let us know what you find - Good Luck!

Dear RAGOTHAM,

There are different reason for C.T.and P.T. failure. System high voltage and spike in the system is the common cause for C.T. and P.T. failure.Following are the posibilties for failure of C.T.and P.T.

1) Open secondary circuit or became high resistive.(for C.T. only)

2) Internal insulation failure due to aging or degradation of insulating oil or paper.

3) Ferro-resonance in the system.

4) Improper creepage distance of the insulator.

5) Higher harmonic level in the system.

RAKHOLIA B.K.

Dear Mr.BKR,

do you mean insulating oil or paper in the transformer?

We have many AC motors on VFDs, SCR controlled heaters, etc.. Is harmonics filters the solution, if so how to specify?

I also wish to inform you that on the same EB feeder there has been PT and CT failures at 4 more consumers factories.

Thanks

Ragotham

Dear Ragotham,

Due to operation of many AC Drives and SCR controlled heaters and other non-linear electrical loads, definitely the power system pollution level increases beyond acceptable /normal level and which may cause ferro-resonance effect and abnormal heating effect in CTs and PTs. This issue must be solved immediately by proper harmonic study of the existing power system and installation of harmonic suppressor reactors, harmonic filters etc.This will prevent further damage of CTs,PTs and other costly electrical equipments. Hiring of electrical consultant in this specialised field is suggested to do the above work.

Manindra