WHAT IS THE PRIMARY INDUCTANCE OF A 20va 50 HZ OR 60 HZ TRANSFORMER?

The model of a power transformer is an inductance in parallel with a resistance that depends on the secondary loading. 20VA tells us about the secondary loading, resulting in a minimum resistance of about

230*230/20 = 2645 Ohms. But we don't know what the idle current is. That would tell us what the inductance is. We could assume it is about 5% of the rated operating current, so the inductance would be about 168Henries for 50 Hz transformer and 140 Henries for 60Hz. Note how a cheap or small transformer has less inductance and therefore more idle current and wasted heat.

I guess it does depend on manufacturer. however the idle current does not add to actual current directly but vectorially. So I would think that even an inductance of 16 henry may b e adequate. At 50 Hz, the idle - no load- current will be about 46ma, but at full load the current will be 98mA as against 86mA if inductance were to be 168H

The formula for inductance is as follows

XL = 2 * Pi * f * L

For 50 Hz this is

XL = 2 * 3.1416 * 50 * 16

XL = 5026.56 ohms

For 60 Hz this is

XL = 2 * 3.1416 * 60 * 16

XL = 6031.872 ohms

Unfortunately, you have not give the coil's resistance or the copper losses of the transformer. This prevents the no load current from being calculated.

If you know the resistance, you can calculate the impedance of the coil with the following formula

Z = Sqrt(R^2 + XL^2)

The current for the coil can then be calculated with the formula I = E / Z.

Then you must add the current required for the copper losses.

I am sure you know you can use a clamp on meter to determine the no load current.

EDIT

It was I who made the mistake, I read (in my mind) "it is about 16 h". I apologize for that.

The actual inductance will vary from manufacturer ti manufacturer. I was working out the reactance based on the inductance being 16 H.

My answer is obviously wrong, if the inductance is not 16 H. There is just not enough data for an answer.

Sorry.

TexMav