Why there is high starting current in induction motor?
This high current in the rotor will create its own magnetic field which opposes the main stator magnetic field, this weakens the stator magnetic field so the back EMF in the stator will drop and the supply voltage will be much higher than the stator back EMF and so the supply current increases to a high value.
Why starting current is high when motors are connected direct on line?
When 3 phase voltage applied across the stator winding for starting of induction motor, high inrush currents magnetize the air gap between the stator and rotor. An induces emf is generated in the rotor windings of the induction motor because of the rotating magnetic field.
Why is starting current of induction motor kept low?
This results a high inrush current but in running condition the secondary circuit that is the rotor circuit provides some restrains that increasing the stator resistance – which keep the current low in running condition in induction motor.
How can we reduce the starting current of an induction motor?
To compensate for the reactive power during starting then a parallel capacitor bank can be used with the motor, either star of delta connected. The capacitances can be calculated for the starting transient and disconnected when the machine has run up to speed. This will help reduce the starting current.
How can I reduce my inrush current?
Inrush current can be reduced by increasing the voltage rise time on the load capacitance and slowing down the rate at which the capacitors charge.
Which AC motor have high starting torque?
DC Series motors have high starting torque but induction motors have wide range of speed control. So, If DC motor is used, then DC drives you can use, although it will be expensive and DC motors are tough to maintain than ac motors due to commutation Problem.
What is difference between VFD and DOL starter?
As a basic starting method, a DOL starter applies full voltage, current, and torque immediately to the motor after the start command. … A VFD converts the AC line voltage to DC voltage, and then inverts it back to a simulated AC voltage for the motor.
Why does current increase when motor load increases?
If the mechanical load increases, the rotor stops a bit (since it’s harder for the rotor to rotate a heavier load), which decreases the counter-EMF. This reduction in the counter-EMF thus increases the current in the coil, and so the power needed from the external voltage source.
When the speed of DC motor is increased?
From the equation. (3) we can say, speed is inversely proportional to armature current. Thus, when the speed of the dc motor is increased, the armature current will decrease. So, the correct answer is “Option B”.
What causes motor overload trip?
Causes may include a large change in load (e.g., a scrap grinder is fed too much at a time), misalignment, a broken drive gear, or improper motor drive settings. Power problems (e.g., low voltage or low power factor) also may cause an overload condition. It’s easy enough to determine the correct size overloads.
How can a motor limit current?
Make sure the load is never so high that the motor stalls or overloads. Make sure that the voltage is so low that the current through the windings will never be higher than rated. Use a current controller to drive the motor that can limit the current at the given maximum.
Why starters are used in induction motor?
The three phase induction motors are self-starting due to rotating magnetic field. But the motors show tendency to draw very high current at the time of starting. … Hence there should be a device which can limit such high starting current. Such a device which limits high starting current is called a starter.