Machine Parts

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 additi...

How does a four point starter overcome the objections of a three point starter? 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 rheostat to a higher resistance value. The current through the shunt field is reduced and is the current through the Coil of the holding electromagnet. The reduced current through the coil reduces the strength of the magnet and makes it susceptible to line voltage variations. In the weakened condition a slight reduction in line voltage would further weaken the holding reduction in line voltage would further weaken the holding magnet, releasing the arm of the starter and thus disconnecting the mother from the line. Unscheduled stoppages of the motor make the three point starter quite unpopular. The four-point starter provides the motor with no-voltage protection. Should the power fail, the motor must be disconnected from the line. If not full line v...