The effects of reluctance and hysteresis with respects towards the magnetic circuits?

Answer 1

You can compare a magnetic circuit to an electric circuit, where

• magnetomotive force is equivalent to electromotive force
• flux is equivalent to current
• reluctance is equivalent to resistance

For a magnetic circuit, the equivalent of Ohm's Law is: flux = mmf/reluctance.

So, for a given value of magnetomotive force, the greater the reluctance, the lower the resulting flux. For example, iron will have a very low value of reluctance whereas air will have a very very high reluctance, so if a magnetic circuit has an airgap, then the overall reluctance of the circuit will be far greater than for a magnetic circuit without an airgap.

Hysteresis comes from a Greek word, meaning to 'lag behind'. It describes how a magnetic circuit's flux density behaves when it is continuously magnetised and demagnetised. For example, when we apply a magnetising force, the flux density increases but, if we then remove the magnetising force, some flux density remains and, in order to remove this, we need to apply a magnetising force in the opposite direction. The amount of flux density remaining after we remove the magnetising force is called 'retentivity' and, for materials such as steel, this is quite large; but for other materials, such as iron, this is very small. So, hysteresis is a way of describing whether a metal is going to be suitable for use as a permanent magnet or for use as a temporary magnet. In particular, we need to understand the significance of hysteresis when choosing a suitable metal to manufacture transformer cores or motor magnetic circuits.

Answer 2

Reluctance in a magnetic circuit refers to the opposition to magnetic flux, which can result in magnetic energy being stored as magnetic potential energy. Hysteresis, on the other hand, pertains to the lagging of magnetization behind the changing magnetic field, leading to energy losses in the form of heat. Both reluctance and hysteresis impact the efficiency and performance of magnetic circuits by affecting the magnetic flux and energy transference within the system.