Tangent Delta Test
Tangent Delta Test
(OP)
Hi,can someone tell me more about tangent delta test especially for auto-transformer i.e. purpose of tangent delta test and test procedures.
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RE: Tangent Delta Test
In both cases we are applying a high-voltage to the insulation (up to 10kv but no more than normal L-G voltage) and measuring the phase angle of the resulting current.
The insulation itself is primarily capacitive (power factor 0.0), but contamination introduces some resisitve component (can raise power factor above 0.0). The higher the power factor, the more likely contamination is present in the insulation. Also the magnitude of the current is also measured which enables calculation of insulation capacitance. All of these parameters can be trended over time for even better diagnostic value. There is a lot that goes into interpreting the data... Doble Engineering is a great resource in this area.
Back to the difference between Tan-delta test and "power factor". In both cases we are characterizing the angle delta between voltage and current. Tan delta is the tangent of this angle while power factor is the cos of this angle. For almost any insulation specimen, this angle will be less than 10 degrees and the cos and tan are virtually identicial. I prefer to talk in terms of power factor because it is a concept already familiar to most electrical types.
RE: Tangent Delta Test
http://www.dse.dk/eng/wire/wire_profile.htm
etc. for more info. It is a generic test not applicable to transformers, only.
RE: Tangent Delta Test
RE: Tangent Delta Test
They ARE very nearly identical for most test specimens. But my reasoning was incorrect.... cos and tan are not equal for small angles, but sin and tan are equal. The tan delta looks at the tangent of the angle delta which is "complementary" to the power factor angle theta (ie delta = 90-theta). The trigonometry gives the same result, since cos(theta)=sin(delta) which is very near to tan(delta).