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Associate

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# Capacitance and Tan Delta Measurements

12/02/2017 6:28 AM

When determining quality of an insulator, sometimes both capacitance and the dissipation factor (tan delta) are measured.

What is the significance of measuring both? Can't measurement say of the dissipation factor only suffice to determine the quality of an insulator?

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Guru

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#1

### Re: Capacitance and Tan Delta Measurements

12/02/2017 10:18 AM
Score 1 for Good Answer
Guru

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#2

### Re: Capacitance and Tan Delta Measurements

12/02/2017 10:18 AM

If you know the cable capacitance, you can then determine the cable leakage resistance from the tan delta. R = C tan(θ).

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#5
In reply to #2

### Re: Capacitance and Tan Delta Measurements

12/05/2017 11:43 AM

That equation is not strictly correct, since it is the impedance leading the voltage and the in-phase impedance that matters. You left out the 2π factor.

Your equation would have been true had you simply mentioned the current ratio.

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#3

### Re: Capacitance and Tan Delta Measurements

12/03/2017 6:31 PM

Yes, the capacitance is of no value when measuring an insulator. They are probably both measured together in an LCR bridge, though. Just the DC resistance might tell you the condition of the insulator. If the problem is related to arcing, too low of test voltage will not find the problem. Dissipation factor (D) = 1/Q, so it is telling you the inverse of the quality of the insulator. There may be cases where the DC value won't find the fault, so the LCR bridge or equivalent might be necessary.

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#4

### Re: Capacitance and Tan Delta Measurements

12/05/2017 11:41 AM

If already doing the tan δ test, you are intrinsically measuring the capacitance as part of the test. Lyn's original link should have told you everything you needed to know.

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Associate

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#6
In reply to #4

### Re: Capacitance and Tan Delta Measurements

12/05/2017 12:03 PM

True. In fact that's why I asked because I have been at a number of factories where they measure both the tan delta and capacitance independtly

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#7
In reply to #6

### Re: Capacitance and Tan Delta Measurements

12/05/2017 12:19 PM

One confirms the other?

Left hand washes the right, etc....

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#8
In reply to #7

### Re: Capacitance and Tan Delta Measurements

12/06/2017 6:46 AM

Thanks

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### Users who posted comments:

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