**broken link removed**
I have a multi tap transformer like in the picture above. I want to learn what happens when I don't use a winding between two taps, and the power distribution when I use multiple windings.
Question #1:
Suppose that I'm using the windings B-C and C-D. Is there any power wasted on the winding A-B when;
a) the transformer is ideal,
b) the transformer is realistic?
With an ideal transformer there is no power lost in winding A-B
In a real transformer the extra losses from unused windings is minimal, and only comes from second-order effects.
The only current flowing in an unused winding is due to the capacitance of the winding, so the current is tiny. The power loss due to that would be so small that it would be very difficult to measure.
Unused windings make a transformer larger than it would otherwise be, so the leakage inductance on the other windings will be larger.
Question #2:
Sin: Power drained from the AC source by the primary windings.
Vxy, Ixy: Respectively the voltage and current between windings X and Y.
Is there a relationship like
Sin = Vab.Iab + Vbc.Ibc + Vcd.Icd
a) the transformer is ideal,
b) the transformer is realistic?
In an ideal transformer there are no losses. However, there will still be power absorbed magnetising the core, that is given out later.
If there is no load, the input inductance means that there will be input current, so the instantaneous power is not zero, although the average power over a cycle will be zero.
So for instantaneous power the equation is incorrect because the magnetising power is not included.
If there are loads, the loads might not be resistive. If the loads are not resistive, the average power is the voltage * current * power factor.
So for average power the equation is incorrect because the power factors are not included.
For a real transformer, the power losses should be added to the equations.
Question #3:
When the transformer is ideal, is there any power drained from the AC source when there is no load connected on the secondary side? If no, what is the explanation?
There is no average power taken by an ideal transformer, but there is current, and instantaneous power, because of the inductance of the primary winding.
Question #4:
Do the wave forms on A-B and B-C corrupt if I drain only the positive alternance of the sine wave on the windings C-D?
In a real transformer, especially smaller ones, the input winding has significant resistance, so when current is taken, the effective input voltage drops, and that will be shown in the unloaded windings.