Phase between two transformers.

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electricity86

New Member
Hello.

I connect two different transformers to the same socket in my home.
I coonect each output to a resistor (different resistors though).
Using two probes and oscilliscope, i present on screen the two resistors' voltages at the same time.
I measure the phase (in seconds) between both signals, and calculate power factor:
Power_Factor = COS(2pi * Phase/Period).

What power factor should i expect?
Do transformers have quite large ESR and capacitance, meaning i should expect a Power_Factor that is not close to 1?

Thanks.

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electricity86

New Member
One more question which is related to the first one:

If I take one of the transformers, and connect its output to both resistors.
Now I measure the phase between the voltages of the two resistors, and calculate Power Factor.
should I expect to receive Power Facot which is very close to 1?
What would you say the max tolerance that the power factor can reach in this case?

Thank you.

ccurtis

Well-Known Member
Hello. I connect two different transformers to the same socket in my home. I coonect each output to a resistor (different resistors though). Using two probes and oscilliscope, i present on screen the two resistors' voltages at the same time. I measure the phase (in seconds) between both signals, and calculate power factor:
Power_Factor = COS(2pi * Phase/Period).

What power factor should i expect? Do transformers have quite large ESR and capacitance, meaning i should expect a Power_Factor that is not close to 1? Thanks.

You should expect the "power factor" (as you define it) to be very near unity. (Power factor is usually applicable to a single load, not between two separate loads.) The ESR is dependant upon the winding resistances of the particular transformers. The ESR will not affect the power factor, because the same current flows through both the ESR and your load resistor. The reactances (capacitive and inductive) of the transformers are insignificant at power line frequencies, but are one reason for slightly less than unity power factor. I am assuming you are using transformers designed for power line frequencies.

One more question which is related to the first one: If I take one of the transformers, and connect its output to both resistors. Now I measure the phase between the voltages of the two resistors, and calculate Power Factor. should I expect to receive Power Facot which is very close to 1? What would you say the max tolerance that the power factor can reach in this case. Thank you.

The power factor (again, as you define it) will be exactly unity. The current through the resistors is the same, therefore, the phase between the voltages across the two resistors is the same (assume pure resistors). In the first example, above this one, if the two transformers are so made and/or resistors so chosen, you could in theory get exactly unity (using your definition of power factor) between the two separate resistors.

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