Transformer Oil Power Factor
Transformer Oil Power Factor
(OP)
Can someone explain the meaning of "Transformer Oil Power Factor". An analysis of our transformer oil indicated a sudden change in Power Factor that gradually began to recover. When we refer to PF, we refer to the relationship of real and reactive power. How does it equate with oil analysis?
Thanks for any help.
Thanks for any help.






RE: Transformer Oil Power Factor
Mathematically, they are quite close at the small loss angles you find in oil. If oil contains water, that usually (always) means that tan(d) increases. Getting rid of water (filter or heating) takes tan(d) back again.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Transformer Oil Power Factor
The formula for real power is I2R and for reactive power is I2X so power factor also expresses the relationship between Resistance and Reactance. A change in power factor may indicate a change in either R or X or both.
Bill
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"Why not the best?"
Jimmy Carter
RE: Transformer Oil Power Factor
Link to ASTM D-924 test protocol for Oil Dissipation Factor
RE: Transformer Oil Power Factor
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(2B)+(2B)' ?
RE: Transformer Oil Power Factor
RE: Transformer Oil Power Factor
I think the bolded portion is incorrect. There is no special definition of power factor used for insulation testing, it is the same power factor as used in circuit analysis. Both are cos of angle between voltage and current, which I assume you're calling delta.
Examples:
Typical motor under load: Current lags voltage by 15 degrees, delta = 15 degrees, pf = cos(delta) = cos(15) = 0.966 (lagging)
Typical insulation specimen: Current leads voltage by 89 degrees, delta = -89, pf = cos(-89) = 0.017 = 1.7%.(leading)
Tan delta is often used abroad to measure the same insulation characteristics that are measured by power factor in US. For typical values small power factor angles below 5%, the two numbers (power factor and tan delta) are virtually the same.
I'm sure this is nothing you don't already know. Sorry if I have misunderstood something what you were saying.
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(2B)+(2B)' ?
RE: Transformer Oil Power Factor
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(2B)+(2B)' ?
RE: Transformer Oil Power Factor
Notation:
[*]pf = cos(theta)
[*]theta = power factor angle = angle by which current lags voltage.
[*]delta = loss angle
[*]delta = theta + 90 degrees
Examples
Typical motor under load: Current lags voltage by 15 degrees, theta = 15 degrees, pf = cos(theta) = cos(15) = 0.966 (lagging)
Typical insulation specimen: Current leads voltage by 89 degrees, theta = -89, pf = cos(-89) = 0.017 = 1.7%.(leading)
Tan delta is often used abroad to measure the same insulation characteristics that are measured by power factor in US. For typical values small power factor angles below 5%, the two numbers (power factor and tan delta) are virtually the same.
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(2B)+(2B)' ?
RE: Transformer Oil Power Factor
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Transformer Oil Power Factor
As an excuse for my misunderstanding, I'll mention that it was somewhat hard for me to follow the logic that suggested "power factor" is a misleading term to apply to insulation...... since power factor is applied in a perfectly consistently manner in both insulation measurements and circuits as I showed above. The less straightforward terminology imo comes from delta and tan delta... new terms to describe something we already know (power factor). It all just depends on what you're used to, I guess.
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(2B)+(2B)' ?
RE: Transformer Oil Power Factor
You have a sample cup filled with oil. Good oil is almost a perfect insulator, so in the sample cup you have a capacitance (essentially fixed: cup geometry and the dielectric constant of oil) so you have much more capacitive current than resistive, giving a LOW (very low) power factor, because you have a high resistance (real power loss) paralleling a very small capacitance.
It the oil is deteriorated, the resistive component changes due to polarized components in the oil, therefore the resistive component is higher. In any reasonable oil sample, there will be little change in the capacitive element, but with "bad" oil, the resistance goes down, the watts loss goes up, but the capacitance stays more or less the same. Therefore, the power factor INCREASES.
These changes are very small. Doble's literature says that oil with a power factor of 0.3% or less is acceptable for service, 0.5% is considered "doubtful" and should be tested by other means, and 1.0% should be investigated, reconditioned or replaced. Of course, the Doble oil power factor test setup is a field test and not as rigorously standardized as a laboratory test.
As to the change in your transformer, remember that the affinity for oil in the transformer is shared between cellulosic components, the paper and wood used in insulation and support, and the oil itself. Hot oil will absorb oil from "wet" cellulose. As the oil cools, the moisture will migrate back to the cellulose, as long as there is enough time for this to take place. If the change is rapid, the water in the oil may precipitate out of the oil, resulting in visible moisture in the tank.
It's all not very static, and that makes it interesting to interpret.
old field guy