Tan (Delta) in Capacitor

It may just be that the angle is convenienty measured as a tangent. E.G For angles near 0 or 90 degrees the sin changes very little with the angle (maximum rate of change being at 45...) whereas the tan will change rapidly with small changes of angle.

Any other suggestion folks?

Feel free to thow things...rotten tomatoes, money, fish?

Yes. Tan(90deg) is infinity.

Bluestone, Del & PW got it: true, tangent 90 = infinity, but that happy condition only applies for *perfect* capacitors...assuming (correctly) that no capacitor (or insulator) is perfect, it does have a (measureable) value, and it changes rapidly with relation to the applied voltage, which we know very accurately.

Indeed, you typically use a Schering-bridge to measure it, e.g.from these guys:

http://www.haefely.com/ (Tettex)

I think these guys make a (small) box that reads it directly:

http://www.pdtech.ch/index1.php

Any good HV text will explain the principle involved (Kuffel & Zaengl, for instance).

Its a good question... But my thoughts are that the function tan is used because the angle is tiny (usually) and the main used sides of the triangle are the capacitive and resistive sides, not the hypotenuse.

So as tan is a function of opposite (resistive) over adjacent (capacitive) it is more easily linked to the actual properties of loss in a capacitor.

I could have got it mixed up above as its many decades since I did Pythagoras at school, but you get the general idea don't you?

John.

hypotenuse in Delta?

you're kiding right? isn't delta configuration a equal phase shift?

No, no ,no delta is the big fan shaped bit where the river deposits silt and splits into smaller rivulets before entering the sea!

(This isn't delta as in star - delta three phase stuff... it's a capacitoor quality measurement thing...)

lol!

very funny. And here's me thinking everyone was talking about my cousins brother in law. Me and Delts haven't been fishing for years.

The measurement you describe is the capacitor dissipation factor which, by definition, is the tangent of the capacitor current loss angle (between 90 degrees and actual). Also, by definition, power factor is the cosine of the phase angle between current and voltage. For loss angles <= 10 degrees, dissipation factor and power factor are essentially identical.

Schering or modified Schering Bridges (C TanDelta Bridges) are frequently used to measure capacitance and dissipation factor because the loss angles are typically small.

U can't get much clearer thant that mate. great mark!