How do you find the starting current of a motor?
You need to check the spec sheet for the motor. The number you are looking for is called Locked Rotor Amps (LRA). This number is usually also on the spec plate attached to the motor, along with the voltage, frequency and running current.
What is starting time of induction motor?
Normally, the starting current of an induction motor is six to eight time of full load current. Plenty of methods have been discovered to start motor in a quick time, but due to un-economic nature, use are limited.
What is the need of starter in 3 phase 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. Such a current can be 6 to 8 times of full load or rated current and it can damage the motor winding.
What is starting current of induction motor?
The starting current of the induction motor is about 5 or 6 times the motor full load current. An induction motor of rating 11 KW,22 Amps,440 volts takes a high starting current of about 132 Amps.
How do you calculate starting amps?
You can multiply the code (amps) times the Horsepower of motor to determine starting amps. Find a list of codes and the amps here. Cycles (Hz) – All U.S. electrical appliances run at 60 cycles per second.
How the starting current is limited?
The main principal of this being the addition of external electrical resistance Rext to the armature winding, so as to increase the effective resistance to Ra + Rext, thus limiting the armature current to the rated value. The new value of starting armature current is desirably low and is given by.
Why motor starting current is high?
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 the current is high at starting in induction motor?
At start, the reactance of the rotor is high because the slip of the motor is equal to unity. The value of Rr/s increase as the slip gets decrease. When the induction motor is started the rotor reactance is more than the rotor resistance and because of the large Xr/Rr ratio the motor takes large inductive current.
What are the disadvantages of a three phase induction motor?
The disadvantages of 3 phase induction motor are: The induction motors have a poor starting torque. As a result, they draw inrush currents causing momentary voltage drop. So the motor is not suitable for high power applications like traction systems etc.
What is purpose of three phase induction motor?
Three-phase squirrel-cage induction motors are widely used as industrial drives because they are self-starting, reliable and economical. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed-speed service,…
What is the principle of 3 phase induction motor?
The working principle of Three phase Induction Motor is basically based on the principle of mutual induction as in case of transformer. The major difference between them is that transformer is static in nature i.e. it doesn’t have any moving parts whereas Induction Motor is a dynamic one.
How does 3 phase induction motors work?
How does an 3-phase induction motor work? In short, it works based on the principle of electromagnetic induction . When the stator windings are supplied with three-phase alternating current, a rotating magnetic field is generated between the stator and the rotor.
