Electrical Machines 1

Chapter Test

Commutation process

Process of rectifying the alternate current into direct current.

Generator

A rotating machine used to convert mechanical energy to electrical energy

Tesla(T)

Unit of flux density in MKS

Gauss(G)

Unit of flux density in CGS

Air Gaps

The space between armature and pole shoe (from top of teeth to pole face)

Rotor

houses the field windings

Stator

rotates in magnetic field

Yoke or Magnetic Frame

It is made up of cast iron or steel. It not only provides mechanical strength to the whole assembly but also carries the magnetic flux produced by the field winding.

Poles and Poles Shoes

are joined to the yoke with the help of bolts or welding and serve two purposes; (i) they support field coils and (ii) spread out the flux in air gap uniformly.

Armature Core

Where the armature conductors are embedded

Armature Winding

The winding where the voltage is induced

Weber(Wb)

Unit of Flux in MKS

Armature Core

The rotor of a dc machine. It is cylindrical in shape with slots to carry armature winding.

Commutator

Physical connection to the armature winding is made through a commutator-brush arrangement. The function of a commutator, in a dc generator, is to collect the current generated in armature conductors. Whereas, in case of a dc motor, commutator helps in providing current to the armature conductors. A commutator consists of a set of copper segments which are insulated from each other. The number of segments is equal to the number of armature coils. Each segment is connected to an armature coil and the commutator is keyed to the shaft.

Reluctance/Magnetic Reluctance

The property of the material that resist the establishment of the magnetic flux

Brushes/Carbon Brush

Are usually made from carbon or graphite. They rest on commutator segments and slide on the segments when the commutator rotates keeping the physical contact to collect or supply the current.

EMF/Electromotive Force

An electric generator is based on the principle that whenever flux is cut by a conductor, an EMF is induced which will cause a current to flow if the conductor circuit is closed.

Magnetic Field, Conductors and Motion of conductor with respect to the magnetic field

essential components of DC machines

Faraday’s law of electromagnetic induction

This law states that when a conductor moves in a magnetic field it cuts magnetic lines of force, which induces an electromagnetic force (EMF) in the conductor.

Flux Cutting Rule

The principle that is the basis for the operation of all machines that convert mechanical motion into electrical energy.

Hall Effect

The creation of voltage across a current-carrying conductor by a magnetic field

Hall EMF

The electromotive force created by a current-carrying conductor by a magnetic field

Commutator/Stator

It provides electrical connections between the rotating coil and the stationary external circuit

October 21, 1831

Date when faraday’s disk was drawn into the diary of Michael Faraday

Rotor

A rotating machine which functions by producing a relative motion between electrical conductors and magnetic field

Brushes

It collects the current from the commutator

Poles Shoes

It spreads out the flux induced in the pole core