Electric machine
Electric machines were developed beginning in the mid 19th century and since that time have been a ubiquitous component of the infrastructure.
A generator forces electrons to flow through an external electrical circuit.
An AC generator converts mechanical energy into alternating current electricity.
Because power transferred into the field circuit is much less than power transferred into the armature circuit, AC generators nearly always have the field winding on the rotor and the armature winding on the stator.
An AC motor converts alternating current into mechanical energy.
It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.
The brushed DC electric motor generates torque directly from DC power supplied to the motor by using internal commutation, stationary permanent magnets, and rotating electrical magnets.
Brushes and springs carry the electric current from the commutator to the spinning wire windings of the rotor inside the motor.
The Ward Leonard set is a combination of machines used to provide speed control.
The magnetomotive force in a PM (caused by orbiting electrons with aligned spin) is generally much higher than what is possible in a copper coil.
Still the magnetic field created by modern PMs (Neodymium magnets) is stronger, which means that PM machines have a better torque/volume and torque/weight ratio than machines with rotor coils under continuous operation.
Brushed machines are machines where the rotor coil is supplied with current through brushes in much the same way as current is supplied to the car in an electric slot car track.
The advantage is that it is possible to control the rotating speed of the machine with a fractionally rated inverter.
Induction eliminates the need for brushes which is usually a weak part in an electric machine.
Since it has two moving magnetic fields in the stator, it gives no meaning to talk about synchronous or asynchronous speed.
Another name is step motor, and it is suited for low speed and accurate position control.
Reluctance machines can be supplied with permanent magnets in the stator to improve performance.
The armature of polyphase electric machines includes multiple windings powered by the AC currents offset one from another by equal phasor angles.
[7] In electrostatic machines, torque is created by attraction or repulsion of electric charge in rotor and stator.
