### Author Topic: How to measure Capasitance and leakage in transformers?  (Read 600 times)

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#### 001

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##### How to measure Capasitance and leakage in transformers?
« on: December 12, 2018, 01:53:04 am »
Hi

How to measure Capasitance in transformers?
- coil to coil
- coil to core
- windings itself cap

And how to read leakage (if DC test ok)?

Is some standard methods?

Thank You
« Last Edit: December 12, 2018, 02:25:15 am by 001 »

#### Berni

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##### Re: How to measure Capasitance and leakage in transformers?
« Reply #1 on: December 12, 2018, 02:14:50 am »
You stick a capacitance meter between the two things you want to measure.

Tho the DC leakage test is often done under high voltage conditions. There are dedicated insulation tester meters for that.

#### 001

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##### Re: How to measure Capasitance and leakage in transformers?
« Reply #2 on: December 12, 2018, 02:23:26 am »
You stick a capacitance meter between the two things you want to measure.

Tho the DC leakage test is often done under high voltage conditions. There are dedicated insulation tester meters for that.

It is not so simply

If I put capasitance meter between coils it will be mistake since coils have its own inductance

DC leakage is not ok too since I`m looking for AC current across coil-to-coil capasitance

#### Berni

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##### Re: How to measure Capasitance and leakage in transformers?
« Reply #3 on: December 12, 2018, 02:47:56 am »
For capacitance you simply wire the two ends of a coil together, that way you get a short connection to the outside edges of a coil so you get a reasonable capacitance measurement. The middle of the coil doesn't matter because its buried under its own windings.

As for testing the current i suppose you can stick a signal generator on there and then test for the current using a multimeter. Since the DC resistance tends to be very high this current would likely be mostly capacitive so you wouldn't gain much more understanding from this unless this for some reason a very important parameter in your design (Do note this is heavily frequency dependent).

#### 001

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##### Re: How to measure Capasitance and leakage in transformers?
« Reply #4 on: December 12, 2018, 03:10:56 am »
For capacitance you simply wire the two ends of a coil together, that way you get a short connection to the outside edges of a coil so you get a reasonable capacitance measurement. The middle of the coil doesn't matter because its buried under its own windings.

Any prooflinks?  You totally misunderstood me in the leakage part

#### T3sl4co1l

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##### Re: How to measure Capasitance and leakage in transformers?
« Reply #5 on: December 12, 2018, 03:36:33 am »
Capacitance between coils is done at a low enough frequency where the self inductance doesn't matter.

Self capacitance is done by measuring impedance over frequency, and modeling the equivalent inductance, resistance (core loss) and capacitance.  (Typically the equivalent circuit also has a number of RLC elements in parallel, representing skin effect, inter-layer capacitance and other complexities, depending on how complex the transformer is, and how accurate the desired model is.)

It can also be predicted using transmission line theory, for which it helps that the transformer was designed from TL theory as well.  A conventional windup in violation of good TL design, can still be estimated in part, in this way, but there will be more uncertainty regarding how much worse its bandwidth will be.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!

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