The soft starter uses this technique to start an induction motor. Reduced Voltage Starter it reduces the supply voltage during motor startup to reduce the inrush current.Full voltage or Across the line starting technique it connects the motor to the full voltage of the supply.The motor starter uses various kinds of techniques to start a motor such as However, they do need overcurrent protection that is available in DOL starter. Small motors below 1Hp does not require motor starter due to their high impedance. These motor starters are usually used for heavy power rated motors. It also offers protections against low voltage & overcurrent. Once the motor gains certain speed, the normal power supply is resumed. In order to prevent such high inrush current, we use motor starters that reduces the initial current for a short duration. Such high currents can also cause huge dip in the line voltage which is dangerous for other appliances connected to the same line. Induction motor cannot tolerate such amount of current as it can quickly damage or burn the windings, reducing the performance & lifespan of the motor. The High inrush current is 5-8 time larger than the full load rated current of the motor. Since the slip is reduced, the impedance of the rotor increases & the motor start drawing normal rated current. the rotor RMF speed approaches near stator RMF speed). Thus the rotor experience torque & as its speed starts increasing the slip of the motor decreases (i.e. The rotor current generates its own magnetic field that try to cancel its cause & starts rotating in the direction of RMF. The alternating current in the stator generates a rotational magnetic field (RMF) that induces current in the rotor windings. Connecting the motor to power supply draws a huge amount of current in the stator winding due to this low impedance called inrush current. It is inversely proportional to the slip of motor.Īt standstill (rest position), the slip of induction motor is maximum i.e. The slip of induction motor is not constant & varies throughout its operation thus the rotor impedance also varies. The rotor impedance depends upon the slip (Relative speed between the rotor & stator) of the induction motor.
It is due to the low rotor impedance of the motor in rest position. It is very essential for safe operation of induction motor. It is due to the low impedance of the windings of the motor at standstill. The induction motors draws a huge amount of current at starting. Since the induction motor is extensively used for various kinds of applications in industries, they need motor starter to safely start & stop it. It also offers protection against overcurrent & low voltage protection. A motor starter is an electrical device that is used for safely starting and stopping an electrical motor.
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