ELECTRICAL POWER AC MOTOR & DC MOTOR
INTRODUCTION • An electrical motor machine that converts electrical energy to mechanical energy in the form of torque and rotation. • The motor is classifies into 2 types:- • Direct Current (DC) motor • Alternating Motor (AC) motor • A DC motor uses DC power supply or a battery as its source of power. • An AC motor is classifies into 2:- • a single phase motor which uses 240V AC power supply, • a three phase motor which uses 415V AC power supply.
INTRODUCTION DC MOTOR AC MOTOR • The unit of power for electrical motor is watt (W). • Horsepower (HP) is also used to determine the power of an electric motor.
DC MOTOR • Commutator e. Shaft i. Carbon Brush • Frame f. Stator Winding j. Fan • Field Pole g. Armature • Ball Bearings h. Terminal Box
BASIC CONSTRUCTIONS The basic construction of a DC motor comprises the stator and the rotor. STATOR • has the field windings which produce the magnetic field flux. • fixed to the frame of the motor which is stationary. ROTOR • located at the centre of the motor is attached to the shaft. • rotates in the electric motor.
BASIC CONSTRUCTION OF DC MOTOR STATOR ROTOR
MAIN COMPONENTS OF A DC MOTOR • Armature • Commutator • Field poles • Carbon Brush • The armature and the commutator are mounted onto the rotor • The fields and the carbon brush are located in the stator.
ARMATURE • The part of the motor that rotates • Receives the electrical energy • Made up of :- • the armature core - functions as an electromagnet, producing the magnetic field that will react with the stator to force produce a rotation from the shaft. • The armature windings - to transform the armature core into an electromagnet when current flows through the windings and causing the armature core to become an electromagnet. • The slots act a path for the armature windings and divide the armature into several segments.
COMMUTATOR • A cylindrical shaped component that mounted in the rotor. • Made up of several segments metal bars that are insulated from one another. • The number of segments depends on the number of armature windings. • Allows the current from the power supply to the armature windings through the carbon brush.
FIELDS POLES • Produce a permanent magnetic field in the DC motor • Small DC motors use the permanent magnets for the field poles • Bigger DC motors use electromagnet produce by field • The windings that produce at the field poles are called field windings.
CARBON BRUSH • Shaped like a small cube acts as a connectors. • The current from power supply flows through the carbon brush via the commutator to the armature windings. • The carbon brush to feed current in and out of the armature windings
PRINCIPLES OPERATION OF A DC MOTOR • The rotation in a DC motor is due to the interaction between magnetic fields (the reaction between the field of the permanent magnet and the field of the armature magnet) • The interaction between these two fields produces a torque that causes the rotor to rotate.
TORQUE GENERATION • The strength of torque produced depends on the strength of the magnetic field of the armature and the field poles. • Figure (a) shows the magnetic flux that exists between the 2 field poles. • Figure (b) shows the direction of the flux in the armature through the commutator. • Figure (c) shows the interaction between magnetic flux and the field poles magnetic flux. This interaction will produce torque.
The direction of the torque is determined by the Fleming Left Hand Rule.
BASIC DC MOTOR CIRCUIT • DC motors are classified into three types: • Series motor • shunt motor and • Compound motor • The classification is determined by the connection between field winding and armature winding and the supply.
SERIES MOTOR • In a series motor, the field windings and the armature windings are connected in series to the supply • The current that flows in the field windings will flow in the armature windings. • When voltage is supplied, there is no back emf in the armature which enables a high initial current to flow in the field windings and the armature windings. • This condition generates a high initial torque. • Thus, the motor is suitable for operating systems with heavy loads
SHUNT MOTOR • Uses a parallel connection for connecting the field windings and the armature windings to the supply • The parallel connection causes the current in the field winding to be constant. The current in the armature winding depends on the back emf. • More suitable when constant speed is required without high initial torque. • Suitable for use in applications such as machine tools, polishers and sprayers.
COMPOUND MOTOR • The combinations of a series motor and a shunt motor. • Has the field windings and the armature windings are connected in series to the supply. • One is connected in series to the armature windings and the power supply. The other is connected in parallel to the supply. • Has a good starting torque and at constant speed • Usually used in heavy load machine. Such as in cutting and grinding.
THANK YOU ANY QUESTIONS?