short-circuittheorytransformer
I'm a newbie with electronic components and I never fully understood why transformers, while essentially being a short-circuit from a wire perspective, don't act like short circuits (i.e. they don't just blindly behave like a waterfall of electrons).
Why is that and how is it related to the "load" attached to the transformer itself?
I'd prefer a 'layman's terms' explanation but I don't mind some math if necessary.
I've never seen a seven-winding transformer but I have dealt with three-winding transformers.
The nameplate information for one particular three-winding transformer is as per below. (Graphic redrawn from photo to avoid showing the full extent of the very large nameplate.)
The impedances given are all on 60 MVA base. In this case tap no. 5 is the principal tapping, so consider the impedances as HV-LV 19.32%, HV-TV 33.08%, LV-TV 9.93%.
The impedance quoted for each pair of windings is with a voltage applied to the first winding, the second winding shorted, and all other windings open circuit. Refer IEC 60076.1:2005 Power Transformers - Part 1: General:
Therefore, assuming --
-- your fault current depends only on the impedance from the HV winding to the particular winding under fault.
In this example, a three-phase fault on the 33 kV winding would produce a maximum three-phase fault current of 60 MVA ÷ 19.32% ÷ 33000 V ÷ √3 = 5.43 kA. A three phase fault on the 11kV winding would produce 60 MVA ÷ 33.08% ÷ 11000 V ÷ √3 = 9.51 kA.
It's not like a solar panel being shorted i.e. the sun stays the same brightness despite the short. A transformer converts electrical energy to magnetic energy and then back to electrical energy. It does it with pretty good efficiency (90%+ on most transformers). If you short the secondary, the primary takes a lot of current. It's the same with an electric motor - if you lock the armature, you take a lot of current/power/energy.
Best Answer
As transformers are usually used with AC rather than with DC, there is what is known as inductance \$L\$, which is a property of a conductor to "resist" the changes in the current flowing in it due to the magnetic fields induced by that current (self-inductance). The magnetic field is "resisting" due to the fact that alternating magnetic field is in turn trying to induce current in the opposite direction. So when we speak of AC, it is an alternating current, i.e. constantly changing which will be resisted by such a conductor. The amount of magnetic field created by a conductor is relative to the density of the conductor windings, so a coil with many windings will create a stronger magnetic field, which in turn will resist more to the changes. In case of transformer, there is an additional coil "sharing" the magnetic field with the primary one, so the magnetic field trying to induce the current in this secondary coil as well. But when it is open, or connected to a load, it is "hard" to induce much current there, so it is "resisting" harder in the primary coil as well. This is pretty much of the intuitive understanding. If you want some math, you can easily find it.