Electromagnetics Principles and Rules in electric machines

Right Hand rule

Rather than having a straight conductor we have coils, If we apply same principle there will be flux like this:

The dashed lines represent the magnetic flux

Faraday’s Law

A steady magnetic field can be produced by steady current

But the steady magnetic field cannot produce a steady current

However if the switch was constantly turned on and off there is a rate of change of flux which induces a voltage then hence a current

If the battery was changed into an AC source and the primary and secondary are not physically connected

The Primary AC Inducts an AC Voltage in the secondary.

Lenz Law

Instead of using a power supply Lenz used a magnet

A permanent magnet

He moved the permanent magnet in and out of the coil which induces a current in such a direction that the field will oppose the change of the magnetic field(produced by magnet)

The induced current wants to oppose the change in the magnetic field and that is called Lenz’s law

Ampere’s Law

For the average Path at the mean radius r , the magnitude field intensity H is related to its source N * I by ampere’s circuital law.

Magnetic Flux density

Magnetic flux phenomena

Fringing

Air Gap Fringing

The flux across an air gap will not be confined to the surface area of the iron core

We can quantify the left region but not right (image)

Leakage

Flux behave non usefully (usually as it passes through the air regions or non preferred magnetic paths instead of the desired path.

Power Flow Diagram

the input power is ideal so there will be joules lost in primary maybe in coil There is also losses in the iron core called iron losses then the remaining power goes to secondary where there is also secondary losses and finally the remaining power goes to output .

Efficiency is given by: