Electrical Engineering ⇒ Topic : Four-point starter
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Gaurav
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Four-point starter : Fig. (a) shows a simplified diagram of a four-point starter. In this starter the drawback/disadvantage of the three-point starter is eliminated. In addition to the same three-points that were used with the three-point starter, the other side of the line, L2 is the fourth point brought to the starter. The coil of the holding magnet is connected across the line when the arm is moved from the 'off position.The holding magnet and starting resistors function as in the three-point starter, The possibility of accidentally opening the field circuit is quite remote; hence the greater acceptance of the four-point starter over the three-point starter Fig. (a) Four-point starter 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 voltage will be applied to the armature without the benefit of starting resistors when power is restored. The holding magnet, being connected across the line, releases the arm when the voltage drops below a specific value, thus protecting the motor when the power is restored | |
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