Tan delta Tests

[govender1]

Could some one please explain what is tan delta testing of transformers.

At my work environment, my colleagues are adamant to conduct these tests as they feel these tests damage the transformers.

Thanks

 

[scottf]

Tan Delta is also called dissapation factor. It's very similar and comparable to insulation power factor. Where power factor is the cosine of the angle between the applied voltage and the insulation charging/leakage current and tan delta is the tangent of that same angle.

For small angles, the difference between the tangent and the cosine is negligable.

Bottom line is that if done properly, it will not damage your transformer. It is mostly applicable to oil-filled units.

 

[DougMSOE]

What scottf said.
Also if properly performed this test con be used on almost every type of electrical power equipment. See Doble Engineering.

 

[sngpl]

If you aren't even sure what C & DF Tesing is all about then I would recommend atleast not to do it yourself. Get a properly trained company or person to do it for you.

 

[Saut]

Also, I'd like to add that if you don't intend to trend your test results, don't do it. Tan Delta testing, like all other preventive maintenance testing, needs proper trending and records. If you're just concerned about safety during energisation, a megger test is sufficient

 

[BMJabbar]

Insultion in transformers are : DC and AC.

DC insulation is measured by Megger, to measure the DC resistance in Giga ohm and DC leakage current.

AC insulation is measured by measuring the capacitance. From the capacitance, some people get the [red]tan[/red] and called tan delta, other people get the [red]cos[/red] and called pf.

Note that there is an argument between Americans and Europeans about conducting Transformer AC insulation.

Americans say it is a must in routine inspections / periodical checks and tests. The most famous brand of capacitance test equipment is Doble. This is why people call it Doble test. This test can be done even for seperate bushings, arresters & oil.

In the other hand, Europeans say Doble test harms the transformer, although they conduct it on bushings, arresters & oil. Also, they say, if it is done on a transfomer and you get a bad reading, it will not show you where is the problem in the transformer.

Still Americans and Eorpeans argue about conducting Doble test on the transfomers.