# Transformer heating

I have difficulty grasping the concept of transformer heating and the overall effect on voltage, current and magnetic induction. I assume that for a transformer to heat up the current should increase as H = I2RT. So the volatge in the secondary coil should drop.

But from what I came across internet it seems that the volatge drop in the secondary coil is not significant when discussing transformer losses. This made me think that perhaps it is due to the load resistance that the heat is produced and thus it should be the current in the which should decrease and voltage increase.

And for the third scenario, if current is decreased then magnetic induction should decrease ( oppose the cause producing it) and voltage should also decrease.

My question is what actually happens to the voltage, current and magnetic induction when a transformer is heated.

• Do you understand the difference between magnetization current and load current in the primary winding? Commented Sep 15, 2021 at 14:38
• I guess. Magnetization current is when the transformer has no load in secondary winding . And load current is when there is a load in the secondary winding which demands more current in the primary winding. I am sorry but I can't seem to relate it with transformer heating. According to this, the current should increase and the magnetic induction should also increase, right?
– mia
Commented Sep 15, 2021 at 14:49
• If something causes the permeability of the core to change, it affects both primary winding and secondary winding equally so, would you really expect induction to alter? Commented Sep 15, 2021 at 15:02

It sounds not a trivial task for a high-school-er. I will try to help, but I wouldn't be able to go in depth with you.

We can say heat with a transformer is from a part of loss. First, I searched "transformer" on WikiPedia. In that page, search (^f) for "heat", and found what causes the heat of a transformer: Winding joule losses, Hysteresis losses, Eddy current losses, and Stray losses. And, it seems those are not only the source of heat, but major losses as well. Meantime, magnetic induction may need to be considered separately from heat and losses.

Winding joule losses: Current flowing through a winding's conductor causes joule heating due to the resistance of the wire. As frequency increases, skin effect and proximity effect causes the winding's resistance and, hence, losses to increase.

Hysteresis losses: "Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core, caused by motion of the magnetic domains within the steel. According to Steinmetz's formula, the heat energy due to hysteresis is given by.."

Eddy current losses: Eddy currents are induced in the conductive metal transformer core by the changing magnetic field, and this current flowing through the resistance of the iron dissipates energy as heat in the core.

Stray losses: Any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat.

Besides the main losses, Radiative losses may not contribute much to heat;

Radiative losses: There are also radiative losses due to the oscillating magnetic field but these are usually small.