- Trending Categories
- Data Structure
- Networking
- RDBMS
- Operating System
- Java
- iOS
- HTML
- CSS
- Android
- Python
- C Programming
- C++
- C#
- MongoDB
- MySQL
- Javascript
- PHP
- Physics
- Chemistry
- Biology
- Mathematics
- English
- Economics
- Psychology
- Social Studies
- Fashion Studies
- Legal Studies

- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who

# Torque Slip Characteristics of 3-Phase Induction Motor

The graph plotted between the torque and slip for a particular value of rotor resistance and reactance is known as *torque-slip characteristics* of the induction motor.

The torque of a 3-phase induction motor under running conditions is given by,

$$\mathrm{\tau_π =\frac{πΎπ πΈ_2^2π _2}{π _2^2 + (π π_2)^2}… (1)}$$

From the eqn. (1), it can be seen that if R_{2} and X_{2} are kept constant, the torque depends upon the slip 's'. The torque-slip characteristics curve can be divided into three regions, viz.

- Low-slip region
- Medium-slip region
- High-slip region

## Low-Slip Region

At synchronous speed, the slip s = 0, thus, the torque is 0. When the speed is very near to the synchronous speed, the slip is very low and the term (π π_{2})^{2} is negligible in comparison with R_{2}. Therefore,

$$\mathrm{\tau_π \propto\frac{π }{π _2}}$$

If R_{2} is constant, then

$$\mathrm{\tau_π \propto π … (2)}$$

Eqn. (2) shows that the torque is proportional to the slip. Hence, when the slip is small, *the torque-slip curve is straight line*.

## Medium-Slip Region

When the slip increases, the term (π π_{2})^{2} becomes large so that π
_{2}^{2} may be neglected in comparison with (π π_{2})^{2}. Therefore,

$$\mathrm{\tau_π \propto\frac{π }{(π π_2)^2} =\frac{1}{π π_2^2}}$$

If X_{2} is constant, then

$$\mathrm{\tau_π \propto\frac{1}{π }… (3)}$$

Thus, the torque is inversely proportional to slip towards standstill conditions. Hence, for intermediate values of the slip, the torque-slip characteristics is represented by a *rectangular hyperbola*. The curve passes through the point of *maximum torque* when R_{2} = π π_{2}.

The maximum torque developed by an induction motor is known as *pull-out torque* or *breakdown torque*. This breakdown torque is a measure of the short time overloading capability of the motor.

## High-Slip Region

The torque decreases beyond the point of maximum torque. As a result of this, the motor slows down and eventually stops. The induction motor operates for the values of slip between s = 0 and s = s_{m}, where sm is the value of slip corresponding to maximum torque. For a typical 3-phase induction motor, the breakdown torque is 2 to 3 times of the full-load torque. Therefore, the motor can handle overloading for a short period of time without stalling.

**Important** – It may be seen from the torque-slip characteristics that addition of resistance to the rotor circuit does not change the value of maximum torque but it only changes the value of slip at which maximum torque occurs.

- Related Articles
- Starting Torque of 3-Phase Induction Motor; Torque Equation of 3-Phase Induction Motor
- Three-Phase Induction Motor Torque-Speed Characteristics
- Torque-Slip Characteristics of Double-Cage Induction Motor and Comparison of Cage Torques
- Running Torque of Three-Phase Induction Motor
- Synchronous Speed and Slip of a 3-Phase Induction Motor
- Split-Phase Induction Motor β Operation and Characteristics
- Construction of 3-Phase Induction Motor
- Rotating Magnetic Field in a 3-Phase Induction Motor
- Methods of Starting Single-phase Induction Motor
- Three Phase Induction Motor Starting Methods
- Three Phase Induction Motor β Working Principle
- 3-Phase Induction Motor β Definition, Working Principle, Advantages and Disadvantages
- Torque-Pulse Rate Characteristics of a Stepper Motor
- Difference between Slip Ring & Squirrel Cage Induction Motor
- 3-Phase Induction Motor Rotor Frequency, EMF, Current and Power Factor