January 2015

The principle of dynamic breaking discussed earlier in connection with poly phase induction motors, also applies well to split phase motors. The procedure, as already explained, is to disconnect the stator windings from ac supply while the motor is running and instead, connect dc supply across the windings. Full wave rectifier is used to obtain […]

The capacitor start motors suffer from the disadvantage that they are not easily reversible due to the centrifugal switch connected in the auxiliary winding. The motor cannot be instantaneously reversed by simple control as the auxiliary winding remains disconnected till the motor comes near to zero speed. However, by proper design of the control circuit

Speed control of split phase motors (without capacitors) is obtained by either pole changing method or by using special winding arrangements. These methods will, however, increase the size of such motors and make them expensive. To obtain two speed operation of a split phase motor, the motor will have two main windings and two auxiliary

The speed of a permanently split capacitor motor can be adjusted by connecting it to a variable voltage source such as an auto-transformer. The limitation of this method is that the starting torque developed is very low, especially when the motor is started on low speed. Another limitation is that speed is sensitive to voltage

There are various methods of controlling the speed of a universal motor. A wide range of speed control is possible by inserting a rheostat in the line circuit which causes variable voltage to appear across the motor terminals resulting in reduced motor speed. Another method of speed control, not very commonly used is by brush

The construction and principle of working of a universal series motor are similar to a dc series motor. To enable the motor to work satisfactorily on ac supply also, some modifications are required in its construction. The important modification required are: (i) Field structure should be completely laminated to avoid losses due to eddy currents:

DC motors are classified into three types depending on the way their field windings are excited. Field winding connections for the three types of dc motors have been shown in Figure. Brief description of different types of dc motors are given as follows: SHUNT MOTOR In this type of motor, the field winding is connected

Control of a machine can be semi-automatic or fully automatic. There are probably more machines operated by semi-automatic control than by manual or fully automatic controls. Consider, for example, an over-head tank which supplies drinking water to a factory. If we provide a manual switch near the pump motor and depute an operator to switch

Having discussed the starting and stopping of a motor by using control devices like push buttons, contactors and over-load relays, we are in a position to discuss the advantages of magnetic control over the manual control. The various advantages are listed as follows: 1) Magnetic control permits installation of power contacts close to motor whereas

When electric motors were first introduced, simple manual switches were used to start and stop the motor. The only protective device used was the fuse. Progress was subsequently made along the lines of improving the reliability, flexibility and make-break performance of the manual switches. In those days one large motor was used to drive a