# Mention three speed control method In a d.c machine

#### BRIEFLY EXPLAIN THE PRINCIPLE OF OPERATION OF THE FOLLOWING SPEED-CONTROL METHODS OF A D.C MACHINE

(I) Fux control. (Ii) Rheostat control. (III) voltage control
1) Flux control: For shunt motor, flux control method is frequently used because it’s simple and inexpensive. In this method, a variable resistance (known as shunt field Rheostat) is placed in series with shunt field windings.For series motor, in this method the flux produced by the series motor is varied and hence the speed. The variation of flux can be achieved in the following ways.
(I) Field diverters. (Ii) Armature diverters (III) tapped field control (IV) paralleling field coils.
(2) voltage control method: In this method, the voltage source supplying the field current is different from that which supplies the armature. This method avoids the disadvantages of poor speed regulations and low efficiency as in armature control method. However, it’s quite expensive.
3) Rheostat control DC shunt motor: In this method, speed variation is accomplished by means of variable resistance in series with the shunt field. An increase in controlling resistance will reduce the field current with a reduction in flux and an increase in

Speed

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### Oluwamuyide Peter

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