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Join Date: Jan 2009
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Tan Delta Testing

01/26/2009 8:16 AM

When performing the tan delta test on a power transformer, which is more effective in diagnosing problems,

1. varying the frequency say from 10 hz to 400 hz and test voltage at a constant value say 10 kV, or,

2. varying the voltage and the frequency constant at 60 or 50 hz?

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Power-User
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#1

Re: Tan Delta Testing

01/27/2009 4:38 PM

It would depend on what the problem is likely to be...

If it has voltage, load or insulation resistance problems, then varying the voltage would most likely produce evidence of the problem.

However if the tranformer has frequency or stablilty issues, (less common), then frequency variations is what would be helpful in diagnosing problems.

i.e. half the battle is knowing what sized "hammer" to use :)

Tony

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#2
In reply to #1

Re: Tan Delta Testing

01/28/2009 6:00 AM

Tony,

Tan delta test is for testing insulation. It's not for testing voltage, load or frequency problems.

Obviously, it is an insulation problem since it is a tan delta test.

Okay, let me put it this way.

What specific insulation problems will show with tan delta performed in low, medium and high frequency or voltage that will not show in 60 hz or nominal voltage tan delta testing?

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#3
In reply to #2

Re: Tan Delta Testing

02/24/2009 4:05 AM

With VARIABLE VOLTAGE AND CONSTANT FREQUENCY(say 50Hz or 60Hz)

Usually Tan delta value should not vary with voltage, it will vary only when the power transformer is tested in very high interferece area.If Tan delta vary with voltage then it indicates that the instrument that is used to measure the tan delta of any transformer has the effect of interference and the tan delta value measured also could be wrong due to interference effect on instrument. So the tan delta value will be constant at different voltage at constant frequency.

With VARIABLE fREQUENCY AND CONSTANT VOLTAGE

This method of testing tandelta is used to detect the moisture content in the transformer insulation. As the study says that the tan delta value will increases linearly as the frequency increases. But if the transformer insulation has some moisture in it then the tandelta value tested at lower frequency (say at15Hz) will be slighly higher than the tan delta value tested at frequency(30Hz).

If we plot a graph of tan delta at various frequency, for a transformer with no moisture (say very low moisture) graph will be linear with respect to frequency, for graph you can refer below

and for a transformer with considerable moisture, in graph their will be a steep high at lower frequency as you can see from the graph below

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Power-User

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#5
In reply to #3

Re: Tan Delta Testing

12/02/2009 12:34 PM

GOOD one........thank you.

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#4

Re: Tan Delta Testing

05/17/2009 10:43 PM

There is a simple way to counter interference in tan delta measurements in high voltage sub stations. Just reverse the test voltage, by reversing the line and neutral so that there is 180 degrees phase shift. Now the interference will act in reverese direction. Take two measurement of Capacitance and Tan Delta one with direct test voltage and other with reversed test voltage.

The average value of the above two measurements will give you the interference free values of both capacitance and tan delta. So no need to vary frequency or voltage just reversal will do

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