How to Increase Starting Torque of a Squirrel Cage Induction Motor
The squirrel cage induction motor operates at base torques and speeds and must attain a steady state through transient start-up. The torque-speed curve represents this process and defines the operating conditions of the motor. Figure 1 shows the key regions of the torque-speed curve. The higher the starting torque, the less the motor will spin, and the lower the speed, the more torque will be produced. To increase starting torque, consider adding a Starter resistor to the motor.
A starter resistor is a simple device that increases the starting torque of a squirrel cage induction motor. These devices are essentially a cylinder that mounts on a shaft. Internally, the rotor contains a number of conductive bars, usually copper and aluminium, that are connected to each other by shorting rings. Their resemblance to a squirrel cage is what gives the motor its name.
The main characteristic of a slip-ring induction model is its high starting torque and low starting current. This type of motor starts on a load, while the rotor conductors are connected in a series with the stator and have an external resistance. As the motor picks up speed, the rings are disconnected and short-circuited. The setup of the Slip-ring motor is similar to that of a squirrel cage induction model.
Electronic soft start
In this study, an ANN-based closed loop soft starting scheme is proposed for increasing the starting torque of a squirrel cage induction motor. We have also included THD into the analysis, which shows that the ANN technique is more effective than FLC. The ANN technique can be further enhanced by utilizing Adaptive Neuro Fuzzy Inference System technology. Genetic Algorithm is also used to fine-tune the ANN-based soft starting.
A squirrel cage induction motor’s maximum starting torque is approximately 7 percent of the rated rotor speed. When all the resistance is present in the rotor circuit, the controller will not start the motor. A contactor, however, will increase the starting torque to a value of one and a half times the full load torque. A typical controller will not start the motor with all of the resistance in the rotor circuit.
Rotor bar skewed
The skewed rotor bar in a squirrel cage induction motor increases the starting torque by increasing the length of the copper bar. The bar is not straight and lies under the alternate harmonic poles of the same polarity. This design increases starting torque and decreases the starting current. The rotor is an important part of the motor. It is essential to keep a careful eye on its performance and conductor bar.
Rotor bar skewed slightly
The AC impedance of the rotor bar of a squirrel cage induction motor depends on the cross-section. When the rotor bar is skewed slightly to increase starting torque, it can be a source of friction and loss. The AC impedance of the rotor bar is lower than that of the inner part at high frequencies. The low-frequency AC impedance of the outer part does not suffer from the skin effect.
Class B motor
If you are wondering how to increase starting torque of your squirrel cage induction motor, there are a few ways you can do so. You can make the motor’s rotor sturdier by reducing its resistance. The rotor is made of four bars, with one bar on each phase. As the rotor turns at a high rate, the current flowing through it will decrease, reducing the starting torque.
Class C motor
The squirrel cage induction motor is one of the most common types of induction motors. It is relatively inexpensive and durable, but it has a poor starting torque. Large starting torque is usually obtained using permanent magnet synchronous motors with rare earth, but these are expensive. By improving the design, starting torque of squirrel cage motors can be increased. Listed below are several methods for enhancing starting torque.
Class A motor
When considering how to increase starting torque of a squirrel cage induction motor, one needs to understand that the starting resistance of an induction motor is directly proportional to its rated torque. However, because the rotor’s fixed resistance is low, it is not possible to adjust this resistance. In fact, starting torque is low due to the high reactance and low power factor. To overcome this, you can increase the starting resistance of your motor. However, increasing the starting resistance may cause copper loss and decrease the efficiency of the motor.
What is the primary reason for low starting torque in a squirrel cage induction motor?
Low starting torque in a squirrel cage induction motor is typically due to the low rotational speed of the motor.
This low rotational speed is a result of the low resistance of the rotor windings.
Why is a high resistance rotor winding desirable for starting torque?
A high resistance rotor winding is desirable for starting torque because it enables the rotor to rotate at a higher speed.
This is due to the increased back EMF generated by the rotor.
What is the relationship between the rotor resistance and the starting torque?
The relationship between the rotor resistance and the starting torque is that the starting torque is inversely proportional to the rotor resistance.
Why is an induction motor typically not started at its rated slip?
An induction motor is typically not started at its rated slip because doing so would result in a very low starting torque.
How can the starting torque be increased without increasing the slip?
The starting torque can be increased by increasing the rotor resistance.
What is the effect of an increase in rotor resistance on the starting torque?
An increase in rotor resistance will increase the starting torque.
How can the rotor resistance be increased without affecting the running torque?
The rotor resistance can be increased by adding a resistor in series with the rotor winding.
What is the effect of an increase in rotor resistance on the power factor?
An increase in rotor resistance will decrease the power factor.
How can the power factor be improved?
The power factor can be improved by adding a capacitor in parallel with the rotor winding.
How does an increase in rotor resistance affect the efficiency?
An increase in rotor resistance will decrease the efficiency.
Is it possible to increase the starting torque without affecting the efficiency?
Yes it is possible to increase the starting torque without affecting the efficiency by using a soft start.
What is a soft start?
A soft start is a technique used to slowly ramp up the voltage to the motor windings.
This prevents the inrush current from damaging the motor.
How does a soft start differ from a hard start?
A soft start differ from a hard start in that a hard start applies the full voltage to the motor windings immediately whereas a soft start slowly ramps up the voltage.
What are the benefits of a soft start?
The benefits of a soft start include reduced inrush current reduced torque pulsations and reduced voltage stressing of the motor windings.
How can the starting torque be increased without using a soft start?
The starting torque can be increased by increasing the rotor resistance.
Jessica Watson is a PHD holder from the University of Washington. She studied behavior and interaction between squirrels and has presented her research in several wildlife conferences including TWS Annual Conference in Winnipeg.