Electra

Single phase motors

                  There are large types of single phase induction motors. Since single phase induction motors is not self starting a second winding namely auxiliary winding is inserted to the stator which provides the necessary displacement for starting and this type is named as split phase induction motor.

 If the inductance or resistance used in the split phase is replaced by the capacitance it is Capacitor start motor. Here the capacitance is used only on starting.

The capacitor is used for starting as well as for run in Capacitor start capacitor run motor.  There is one motor which operates on AC and DC which is known as Universal motor. It is used in blowers, hair dryers and sewing machines.

The application where there is a need for constant speed and high torque we can make use of Repulsion motor. It consists of single stator winding with two rotor winding. Shaded pole motor consists of shading coil of low resistance copper ring which gives the torque.

It is used in clocks and small fans where the power requirement is less.

Speed Management of a Direct Current series motor

                There are various methods to control the speed of series motor

. 1) The variation of flux by means of field diverter in which the variable resistance is connected in parallel with the field winding. If the speed has to increase the resistance is reduced which results in the reduction of main field.

2) The variation of flux by means of armature diverter gives speeds below the normal value. It is obtained by connecting the diverter across the armature.

 3) In the Tapped field method the higher speeds results by cutting out the series turns while with the full field motor runs as its minimum speed.

4) The variable resistance in series with the motor helps in controlling the speed. If the resistance increases the voltage across motor reduces. Since the voltage is proportional to speed the speed drops. T

he demerit of this method is the wastage of power as the resistance is in series.

Shunt Motor Versus Compound Motor

                            The field winding of the motor connected in parallel to the armature is known to be Shunt Motor.

Here the field consists of many turns of fine wire since it does not carry the entire armature current. The current path is divided to go to armature and field.

The Shunt motor is a constant speed motor because speed of the shunt motor remains practically constant with varying loads.

It is used where the constant speed operation is necessary. It is widely used in Lathe machines where one speed is maintained constant for a longer period.

The compound motor consists of both the shunt and series winding which is required for certain applications. Both the fields can be varied to operate the motor nearer to series or shunt motor.

When it operated nearer to series motor it is known as cumulative compound and when it is nearer to shunt motor it is known as differential compound.

Series motor has the disadvantage that we cannot operate it in decreasing light loads which can be overcome by this compound motor. It is also used in applications where there is a fluctuating load.

Introduction to Series Motors

            The field of DC motor connected in series of armature is Series motor. Here the winding is made up of thick wire as it passes the full armature current through it.

The armature current is same as that of field current in DC Series motor. Speed and Torque of the motor determines its application. When there is light load the torque developed is less and the speed is higher but at heavy loads the speed is small and the torque is higher.

The series motor is used in variety of application because of it has higher starting torque. So it is useful for lifting heavy loads in cranes, electric trains and trams.

The series motor should not be operated in low loads. Since the torque is inversely proportional to the speed in decreasing loads the speed will increase dramatically to the dangerous extent. It is wise to use series motor in applications where the demand requirement is higher.

DC Motors – Principle and Operation

                 The Motors plays a major role in this current era. It is a machine which provides us the mechanical energy when the electrical energy is supplied to it.

It works on the law of interaction. The conductors are placed in the slots of the armature periphery which carries current. Since the armature is placed in the magnetic field it results in the development of torque.

The mechanical force developed makes the armature to rotate. As we know that emf will be generated when the current carrying conductor cuts the magnetic field.

The emf produced is the back emf in the DC Motor. It opposes the input voltage supplied to the armature.

The mechanical energy produced from the motor can be used in large industries. It is necessary to know about the shaft torque at this point.

 All the developed torque is not available for the useful work. The Torque obtained for the useful work can be described as the Shaft Torque.