Hello friends, I hope all of you are doing great. In today’s tutorial, we are gonna have a look at the Maximum (Pullout) Torque in an Induction Motor. The maximum or pull-out torque of the three-phase induction motor three-phase induction motor is the extreme bearable torque which motor can produce without any sudden decrease in its regular speed but for a short time interval. If the motor stays to work at its maximum or pullout torque, it will produce serious damage for the rotor of the motor and in conclusion, the speed of the motor will steadily slow down and motor stops to works.
In today’s post, we will have a look at how torque produced in the motor and its facts. So, let’s get started with the What is the Maximum (Pullout) Torque in an Induction Motor.
What is the Maximum (Pullout) Torque in an Induction Motor
- As we have discussed in the previous article that the induced torque in the induction motor is found by this equation.
Tind = PAG/Wsync
- The maximum (pullout) probable torque exists when the air-gap power (PAG) is extreme. As the air-gap power (PAG) is equivalent to the power spent in the resistance (R2 /s), the maximum (pullout) induced torque will arise when the power loss by that resistance is extreme.
- As we can see that in given circuit diagram, if we apply maximum power transformer theorem to this circuit, maximum power transfer theorem says that the maximum (extreme) power transmitted to the output (in this circuit the output is (R2/s) ) if the impedance (Z) at the output equals to the impedance at the input.
- The correspondent source impedance (Z) in the circuitry is given as.
Zsource = RTH + jXTH + jX2
- Thus, the maximum transfer of power will exit when this given below equation we get.
R2/s = √(R2TH + (XTH + X2)2)
- By resolving this equation, we can find the value of slip at the maximum (pullout) torque of induction motor which is given below.
Smax = R2/√(R2TH + (XTH + X2)2)
- From this equation, you can note that rotor resistor (R2) exits at the numerator of this equation, thus at maximum (pullout) torque slip (S) of the rotor is directly proportionate to the resistance (R2) of the rotor.
- To find the equation of extreme torque we put the slip equation in the given expression.
Tind= (3VTHR2/s)/ Wsync[(RTH+R2/s)2+(XTH+X2)2]
- This induced torque equation we have determined in the last article which is Derivation of the Induction Motor Induced-Torque Equation you can read it to get this expression.
- After putting the slip equation in induced torque equation get the expression of the maximum torque.
Tmax = 3V2th/(2wsync[RTH +√(R2TH + (XTH + X2)2)]
- From this equation, we can see that the maximum torque of the induction motor is proportionate to the square of the input voltage (V) and inverse proportionate to the impedance of the rotor and reactance of the rotor.
- If the motor has a smaller value of reactance, then it will have a large amount of maximum torque.
- From the slip equation, we can observe that the slip at which maximum torque exits is directly proportionate to the resistance of rotor, but from the maximum torque equation we can see that the maximum torque does not depend on the value of resistance of rotor.
Effect of varying rotor resistance on the torque-speed characteristic of a wound-rotor induction motor
- The torque-speed characteristic curve for a wound rotor induction motor is drawn in the given diagram.
- Remember that it is feasible to add resistance into the rotor circuitry of a wound rotor as the rotor circuitry is brought out to the stator over slip rings.
- You can note from the diagram that as the resistance of the rotor upsurges the pullout speed of motor declines, but the maximum (pullout) torque does not vary.
- It is likely to take benefit of this characteristic of wound-rotor induction motors to start very weighty loads.
- If resistance is adding to the rotor circuitry, the maximum (pullout) torque can be set to exits at initial situations.
- So, the maximum conceivable torque would be accessible to start weighty loads.
- On the other hand, when the load is rotating, the additional resistance can be detached from the circuitry, and the maximum (pullout) torque will transfer to near-synchronous speed (wsync) for the steady process.
So, friends, it is all about Maximum (Pullout) Torque in an Induction Motor, if you want to know something else about it ask in comments. Thanks for reading. See you in the next tutorial.
You can also read some related articles to the induction motor. That is described here.
- Introduction to Induction Motor
- Introduction to Three Phase Induction Motor
- Equivalent Circuit Induction Motor
- Induction Motor Torque-Speed Characteristics
- Variations in Induction Motor Torque-Speed Characteristics
- Power and Torque in Induction Motors
- Induction Motor Design Classes
- speed Control Method of Induction Motors
- Induction Motor Design
- No-load Test of Induction Motor
- Solid State Drive Induction Motor
- Derivation of the Induction Motor Induced-Torque Equation
- Induction Motor Induced-Torque Equation