The commutator is a device which converts alternating induced emf in a generator to DC emf. In case of motor it produces unidirectional torque.
Electric motors applications are: industrial f, blowers and pumps, machine tools, household appliances, power tools, and disk drives, record players.
A series-wound motor is known as a universal motor when it has been designed to operate on either AC or DC power. It operate well on AC because the current in both the field and the armature (and hence the resultant magnetic fields) will alternate in synchronism and hence, the resulting mechanical force will occur in a constant direction of rotation.
They are working on the fundamental principle based on Faraday’s Laws of Electromagnetic Induction.
This law states that, When a current carrying conductor moves in magnetic field, it induces an EMF.
An AC motor is an electric motor driven by an alternating current (AC). 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.
Advantages of AC Motors:
Disadvantages of AC Motors:
Advantages of DC Motors:
Disadvantages of DC Motors:
Three phase motors are having
compared to the single phase motors.
Turbo alternators are high speed alternators. Because of high speed of rotation, the rotor diameter is reduced and the axial length is increased. Two or four poles are generally used and steam turbines are used as prime movers.
Generally in alternators, the armature is stationary and the field rotates. Small low-voltage alternators often have a rotating armature and a stationary field winding.But in large alternators rotating armature field type is used.
The distance between the centres of two adjacent poles is called pole pitch. One pole pitch is equals to 180 electrical degrees. It is also defined as the number of slots per pole.
Three phase Induction motor is nothing but a rotating trformer.
If the coil span is less than the pole pitch, the winding is called as shot-pitched winding. It is also known as short-chorded winding.
If the coil span is equal to pole pitch, the winding is called as full pitched winding.
An electric motor is an electrochemical device that converts electrical energy into mechanical energy. Most electric motors operate through the interaction of magnetic field and current carrying conductors to generate force.
The distance between the two coil sides of a coil is called as coil span. It may be expressed in electrical degrees or in number of slots.
For the generation of emf, there should be two basic systems.
For having smoother output voltage from DC machines its commutation must be as ideal as possible.
In order to have good commutation the flux density in the air gap must decrease gradually from maximum value under the centre of the pole to zero on.
The Motor Principle: when a current-carrying conductor is located in an external magnetic field perpendicular to the conductor, the conductor experiences a force perpendicular to itself and to the external magnetic field.The physical principle behind production of mechanical force by the interactions of an electric current and a magnetic field.
The right-hand rule for force on a conductor can be used to determine the direction of the force experienced on the conductor.
The advantages are:
The disadvantages are:
Mainly there are two types of electric motors:
In any electrical machine ( AC/DC motor or generator) the stationary member is called as stator. Similarly in all machines the rotating member is known as rotor.
The series filed winding is always connected in series with the armature and thus has to carry the armature current which directly gets decided by the load.
Thus the current passing through series field winding is of high level.
The voltage drop across series field winding gets added to the voltage drop across armature winding while deciding the back emf. This voltage drop must be very small.
Hence as the current through series field winding is high, in order to keep voltage drop across it to a small value, its resistance is very low.
On the other hand, the shunt field winding is directly connected across the rated supply voltage hence to limit current through it, resistance is very high.
When the core is laminated and insulated from each other with paper or varnish the eddy current loss is minimized.
A DC motor is a mechanically commutated electric motor powered from direct current (DC). The stator is stationary in space by definition and therefore so is its current. The current in the rotor is switched by the commutator to also be stationary in space. This is how the relative angle between the stator and rotor magnetic flux is maintained near 90 degrees, which generates the maximum torque.