The major advantage of shunt motor is its ease of speed control. With the use of rheostat in the shunt field circuit, the field current and flux per pole may be varied at will, and variation of flux causes the inverse variation of speed to maintain counter emf approximately equal to the impressed terminal voltage. A maximum speed range of about 4 or 5 to 1 may be obtained by this method. By variation of impressed armature voltage, very wide speed ranges may be obtained.
