Explain the working principle of electromagnetic induction is used to make generators?

Answer 1

In an induction motor, a rotating magnetic field is sent sideways through the walls of a copper cylinder. The field cuts the copper, generating a current in it, and also a powerful magnetic field, and the magnetic field in the copper repels the rotating field. This 'pushes' the copper forward, making the coper try to move. If the copper cylinder is able to spin freely, it will coast along at a slightly slower speed than the rotating field, as the moving magnetic field has to keep 'cutting' the copper to create the other magnetic field. In this case the rotating cylinder is not doing any work, since no energy is being used to drive a load. It's just coasting frictionlessly.

If we place a friction load upon the motor shaft, (add a washing machine,) then the copper cylinder will slow down in the magnetic field moving through it. In this case the magnetic field is cuts the copper faster, generates more current and flux, and pushes the copper along harder, so the device becomes a motor. Energy from the rotating magnetic field sets up an opposite field in the copper cylinder, and drives it forward.

If instead we *drive* the copper cylinder forward, making it spin at a faster speed than the moving magnetic field, then the copper cylinder will push the field forward, creating a rotating field in the copper, and this generates electrical energy in the coils.

So for a 2-pole motor running at 60Hz, it becomes a motor if it spins slower than 3600RPM, and it becomes a generator if it's spun faster.

Here's a second way to visualize things: the rotating copper cylinder generates its own trapped magnetic field. This means that the copper cylinder is itself a magnet. If this magnet is allowed to spin freely, then it will turn at exactly the same rate as the magnetic field from the coils. Then if we grab the motor shaft to try to slow down the spinning "copper magnet," the poles of the magnet within the copper will lag behind the moving magnetic poles from the coils, and the coils will pull the copper strongly forward. The "copper magnet" doesn't need to slow down, but instead it will suck energy out of the coils as its gets dragged forward by the moving poles from the coils. On the other hand, if we try to spin the "copper magnet," it won't turn faster. Instead its poles will get ahead of the moving poles of the coils, and it will inject electrical energy into them, and drive the mains with this energy. In other words a moving magnet can generate a current in a nearby coil, *OR* a current in a coil can force a nearby magnet to start moving. All motors are generators and all generators are motors. It just depends on which side is driving forward and which side is being dragged along.

If induction motors and generators make your brain hurt, just remember that there's a good reason for this. They weren't invented by a bunch of engineers. Instead they sprang from the twisted mind of Nikola Tesla, who no doubt could ride along with his mental squirrel-cage rotor while seeing how the fields and currents behaved.