6.6kV to 415 ONAN Transformer Maintenace 5

[jsearl]

We have 3no. 2MVA 6.6kV to 415 volt transformers on site and I want to put together an enquiry for a contractor to inspect them and report and then undertake any necessary maintenace on them. What would anybody suggest I ask for in my enquiry (works specification) documents.

Thanks in advance for any help.

 

[EEIre]

Suggest the following:

1) Insulation resistance test
2) Oil analysis
3) Testing on instrumentation (oil level, oil temp, etc)

Regards

Sean

 

[ScottyUK]

Hello jsearle,

I agree with the above, but add in the following:

Low resistance measurement of the windings at a reasonably high current. You'll need a true DC source, as the mains-powered types have significant AC ripple which produces inaccurate results on a highly inductive load like a transformer winding.

Check joint torque on bushings, especially if transformer has seen cyclic service.

Physical inspection of the bushings and seals for cracking or leakage.

Check your earthing (grounding in US) arrangements.


Scotty.

 

[jbartos]

Suggestion: The transformer grounding, protective relaying, etc. should not be ruled out. Also, the transformer manufacturer might be contacted for recommended transformer inspections, testing, and maintenance/repairs.

 

[DanDel]

Turns ratio on all taps and Doble Power Factor tests are typically performed also along with the other tests mentioned. The NETA spec for testing is quite helpful for all electrical equipment. Search this forum for more info about NETA.

 

[ignitorgun]

Good Day jsearle,

I agree with those above suggestions. you should also include the winding resistance test to ensure the same resistances between windings. For the oil analysis ,aside from Dielectric breakdown voltage test it is necessary to have laboratory test such us total acidity number test, water content and color test, also the dissolved gas formation. For SOP Annual Preventive maintenance test is required for all the transformer so that the substation engineer will know the trend of the transformer.