Electrical Machines 1

• A DC machine is one in which the source of energy is a direct current (DC) source.
• Energy cannot be created nor destroyed as it can only be transformed from one form to another.
• Electromechanical energy conversion is the link between electrical and mechanical system.
• electrical input -> motor -> mechanical output
• mechanical input -> generator -> electrical output
• Dynamo is a rotating machine that converts mechanical energy into electrical energy, and electrical energy into mechanical energy.
• Principles of a dynamo are generator action and motor action
• generator action develops voltage
• motor action develops force or torque
• DC generator are similar to DC motors in appearance and construction.
• The common parts of a DC generator are magnetic frame, pole coils or field coils, pole cores and pole shoes, armature core, armature winding, commutator, and brushes and bearings.
• Magnetic frame provides mechanical support for the poles.
• Magnetic frame acts as protecting cover.
• Magnetic frame carries the magnetic flux produced by the poles.
• Field magnets are consist of pole cores and pole shoes.
• One of the purpose of pole shoes is to spread out the flux in the air gap.
• Pole cores reduce the reluctance of the magnetic path.
• Pole cores and pole shoes support exciting coils.
• Pole coils consist of copper wire or strip
• Field windings are constructed into three types: (1) shunt field, (2) series field, and (3) compound field.
• Compound field winding consists of both shunt and series fields.
• Shunt field consists of many turns of fine wire
• Series field has fewer turns but thicker wire than shunt field
• Armature core houses the armature conductors or coils.
• Armature core causes the coil to rotate and cut the magnetic flux of the field magnets.
• armature winding is the heart of the dynamo
• commutator facilitates the collection of current from the armature conductor
• brushes are used to collect current from the commutator
• commutator converts the current induced in the armature conductor into unidirectional current.
• brushes are made of carbon
• brushes are held stationary in position by brush holders
• ball bearings are employed to freely rotate the commutator shaft
• shafts are made of steel that holds the commutator
• conductor is the length of wire lying in the magnetic field and in which an EMF is induced
• coil span or coil pitch is the distance measured in terms of armature slots between two sides of a coil