What protection does the four point starter offer ? The use of three point starter presents a problem .The speed of the motor is controlled by means of the field rheostat .To increase the speed of the motor it is necessary to set the field resistance to a higher value .The current through the shunt field is reduced and so is the current through the coil of holding magnet . The reduced current through the coil reduces the strength of the magnet. Thus it makes motor susceptible to line voltage variations .In the weakened condition a slight reduction in line voltage would further weaken the holding magnet , releasing the arm of the starter and thus disconnecting the motor from the connection line. As a result unscheduled stoppages of the motor makes the three point starter quite unpopular. The four point starter eliminates the disadvantage of three point starter .In addition to the same three point starter the other side of the line ,L2,i
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