## Equivalent circuit of induction motor

## Lecture 40: equivalent circuit of 3-phase induction motor

On the left, a three-phase totally-enclosed fan-cooled (TEFC) induction motor with end cover, and on the right, a TEFC induction motor without end cover to reveal the cooling fan. Interior heat losses in TEFC motors are dissipated indirectly by enclosure fins, primarily through forced air convection.

Cutaway view of a TEFC induction motor’s stator, displaying the rotor and internal air circulation vanes. Since many of these motors have a symmetric armature, the frame can be turned around to position the electrical link box (not shown) on the opposite side.

The electric current in the rotor used to generate torque is obtained by electromagnetic induction from the magnetic field of the stator winding in an induction motor, also known as an asynchronous motor.

1st As a result, an induction motor can be built without any electrical connections to the rotor. [a] [a] The rotor of an induction motor may be wound or squirrel-cage style.

Since they are self-starting, dependable, and cost-effective, three-phase squirrel-cage induction motors are commonly used as industrial drives. Single-phase induction motors are often used for smaller loads, such as fans in the home. Induction motors, which have historically been used in fixed-speed applications, are increasingly being used in variable-speed applications with variable-frequency drives (VFDs). VFDs in variable-torque centrifugal fans, pumps, and compressor load applications provide particularly significant energy savings opportunities for current and future induction motors. Induction motors with squirrel cages are commonly used in fixed-speed and variable-frequency drive applications.

## Induction motors vi: equivalent circuit of the induction motor

The Equivalent Circuit of an Induction Motor allows for the evaluation of output characteristics in steady state conditions. An induction motor operates on the theory of voltage and current induction. For operation, voltage and current are induced in the rotor circuit from the stator circuit. An induction motor’s analogous circuit is identical to that of a transformer.

As compared to a transformer, the total magnetizing current I0 of an induction motor is substantially higher. This is due to the induction motor’s air gap, which causes a higher reluctance. As we know, the no load current in a transformer ranges from 2 to 5% of the rated current, while the no load current in an induction motor ranges from 25 to 40% of the rated current, depending on the motor size. In an induction motor, the magnetizing reactance X0 is also very small.

A voltage is generated in the machine’s rotor windings when a three-phase supply is applied to the stator windings. The greater the relative motion of the rotor and stator magnetic fields, the greater the rotor voltage that occurs. At a standstill, there is the greatest relative motion. The locked rotor or blocked rotor condition is another name for this problem. The induced voltage at any slip is given by the equation below if the induced rotor voltage at this condition is E20.

### Induction motors xii: equivalent circuit of the induction motor

This paper proposes a new equivalent circuit for medium voltage and high-power induction motors that takes into account the manufacturer’s more comprehensive details. The equivalent circuit has the advantage of enabling the electrical measurement of all power losses and the realization of the power balance, so a technique for obtaining its parameters is provided. A new method of measuring and describing additional losses using a resistance in the rotor circuit is a result of this work. Then, as part of a power balance, three types of losses are considered: conventional or joule effect variable losses, persistent losses, and additional losses. The suggested approach is non-iterative and straight. It was tested on a 6000 V, 2500 kW case study motor at the Maximo Gomez Power Plant in Cuba.

### Equivalent circuit of the three phase induction motor

An induction motor’s stator model has a stator phase winding resistance R1 and a stator phase winding leakage reactance X1. These two parts can be found on the right side of the computer model. A pure inductive reactor X0 takes the magnetizing part I and a non-inductive resistor R0 carries the core-loss current I0 to simulate the no-load current I0.

In an induction motor, the magnetizing reactance X0 would be much lower. I0 is approximately 2 to 5% of the rated current in a transformer, while it is approximately 25 to 40% of the rated current in an induction motor, depending on the motor size.

When a 3 supply is applied to the stator windings of an induction motor, a voltage is produced in the rotor windings of the unit. The higher the relative motion of the rotor and stator magnetic fields, the higher the rotor voltage that results. When the rotor is stationary, the highest relative motion occurs, which is known as the Standstill state. The condition is also known as “closed rotor” or “blocked rotor.”