Answer Posted / boo123pavani

In three point starter NVR (no voltage relay)is series with
Shunt if voltage falls certain value NVR De energized due to
insufficient magnetic field and motor turned off. But in
four point starter NVR energized directly from DC supply
thus the draw back of 3 point starter rectified


A motor can be run for a higher speed than normal speed by reducing the field current. reduced the field current may not produce enough magnetic force to hold the handle in on position. so handle returns to off position. this is the disadvantage of three point starter.this is the advantage of four point starter. it will not returns to off position

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