Table of Contents
- 1 Why does induction motor have low starting torque?
- 2 Why is the no load current drawn by 3 phase induction motor so high?
- 3 What causes a 3 phase motor to draw high amps?
- 4 What causes high amps on motors?
- 5 What is the starting torque of 3 phase induction motor?
- 6 How will you improve the starting torque of 3 phase induction motor?
- 7 How to choose the right motor for your load?
Why does induction motor have low starting torque?
It suffers from the disadvantage of a low starting torque. It is because the rotor bars are permanently short-circuited and it is not possible to add any external resistance to the rotor circuit to have a large starting torque.
Why is the no load current drawn by 3 phase induction motor so high?
As the air gap between the stator field winding and rotor winding is large, the more magnetizing current is needed to create flux which will cut the rotor conductor. So it is an important reason why Induction Motor draws more No Load Current than a transformer.
Do 3 phase motors have a low starting torque?
Single Phase induction motor uses single phase supply, for its operation. Three Phase induction motor uses three phase supply, for its operation. The starting torque is low. The starting torque is high.
How do you increase starting torque on an induction motor?
There are three ways to improve the starting torque of Single phase induction Motor
- Internal Rotor Resistance. The across the line starting torque at low speed can be increased by increasing the rotor resistance.
- External Rotor Resistance.
- Variable Voltage/Frequency.
What causes a 3 phase motor to draw high amps?
Probable causes of high current with load include mechanical overload, excessively high magnetic flux densities and, less frequently, an open rotor. An error in winding data that results in lower-than-design-level magnetic flux also can cause high current with load.
What causes high amps on motors?
What Causes a Motor to Draw Higher Amps? Motors require a certain output in watts in order to function, and this is the result of a voltage multiplied by amps. So when voltage falls, resistance scales up in order to supply the difference, and the motor will also draw more current.
How can you increase the starting torque of a three phase induction motor?
The starting torque of a three-phase induction motor can be…
- Increasing rotor reactance.
- Increasing rotor resistance.
- Increasing stator resistance.
- None of the above.
Why does a three phase motor have such high in rush current on start up?
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.
What is the starting torque of 3 phase induction motor?
A 3-phase induction motor has a starting torque of 100\% and a maximum torque of 200\% of the full load torque.
How will you improve the starting torque of 3 phase induction motor?
Therefore by reducing the cross-sectional area of rotor bars and by changing the conductor material, we can increase the rotor resistance. So by doing this Starting torque of the induction motor can be increased. An induction motor is similar to a poly-phase transformer whose secondary winding is short-circuited.
Why does induction motor have large current at start up?
Unlike in DC motors, large current at starting is due to the absence of back emf. If an induction motor is directly switched on from the supply, it takes 5 to 7 times its full load current and develops a torque which is only 1.5 to 2.5 times the full load torque.
From the torque equation of a three phase induction motor, the starting torque is approximately proportional to the square of the applied voltage. That means, if the applied voltage is 50\% of the rated value, the starting torque will be only 25\% of its normal voltage value.
What is the starting torque of a motor?
The rotating force that a motor develops is called torque. Due to the physical laws of inertia, where a body at rest tends to remain at rest, the amount of torque necessary to start a load ( starting torque) is always much greater than the amount of torque required to maintain rotation of the load after it has achieved normal speed.
How to choose the right motor for your load?
The more quickly a load must accelerate from rest to normal rotational speed, the greater must be the torque capability of the motor driver. For very large inertia loads or loads that must be accelerated quickly, a motor having a high starting torque should be applied.