Mell Why induction motor is started at no load?
Theory of No Load Test of Induction Motor The impedance of magnetizing path of induction motor is large enough to obstruct flow of current. Therefore, small current is applied to the machine due to which there is a fall in the stator-impedance value and rated voltage is applied across the magnetizing branch.
Why should induction motors not allow to run under no load or light load conditions?
At low load or no load condition because of presence of only magnetizing current in the stator windings, causes low power factor operation of the power system, since magnetizing current is highly inductive in nature.
What is no load in induction motor?
The no-load test of an induction motor is similar to the open-circuit test of a transformer. The motor is not connected from its load, and the rated voltage at the rated frequency is applied to the stator to run the motor without a load. The 2-wattmeter method measures the input power of the system.
When motor runs on no load then?
When the motor is connected across the supply mains without load, it draws small current from the supply mains. This current will flow through the series field and armature, the speed tends to increase so that back emf may approach the applied voltage in magnitude.
Why the no load current drawn by the 3 phase induction motor is so high?
The RMF in a motor has to travel thru a high reluctance path {air gap} twice. That makes it draw a higher current from the three phase line. Hence it’s line and no load currents is higher. In case of a 3 phase transformer, whole flux passes thru the lower reluctance path {iron core}.
What will be the efficiency of motor at no load?
Normally, electric motors are designed to have high efficiency at or near full load. at no load efficiency is zero (as output is zero). at part load efficiency may be maximum is fixed losses and variable losses of the motors become equal.
Which loss in the motor is significant in no load test Why?
As the motor is running at no load, the total input power is equal to the constant iron loss, friction, and windage losses of the motor. Since the power factor of the induction motor under no-load condition is generally less than 0.5, thus the Wattmeter reading of one of the Wattmeter will show a negative reading.
What type of motor should never be operated at no load?
A series motor should never be started at no load. With no mechanical load on the series motor, the current is low, the counter-EMF produced by the field winding is weak, and so the armature must turn faster to produce sufficient counter-EMF to balance the supply voltage. The motor can be damaged by overspeed.
Why does starting current of induction motor is high-Inst tools?
Once the rotor starts picking up the speed, current drawn by the machine decreases. The time required for staring of the motor depends on the time required for the acceleration which depends on the nature of the connected load. High inrush currents drawn by induction motor during starting can result in large dip in connected bus voltages.
What are the disadvantages of an induction motor?
Disadvantages of High Starting Currents in Induction Motor: High inrush currents drawn by induction motor during starting can result in large dip in connected bus voltages. This dip in bus voltages can impact the performance of other motors operating on the bus.
What is the impedance of an induction motor?
The impedance of magnetizing path of induction motor is large enough to obstruct flow of current. Therefore, small current is applied to the machine due to which there is a fall in the stator-impedance value and rated voltage is applied across the magnetizing branch.
What is the running light test for induction motor?
This test is also well-known as running light test. This test is used to evaluate the resistance and impedance of the magnetizing path of induction motor. The impedance of magnetizing path of induction motor is large enough to obstruct flow of current.