There are many similarities and differences between the induction motor and transformer.
Similarities between Induction motor and Transformer
- The Induction motor is similar as a Transformer with a rotating short-circuited secondary.
- The stator winding in induction motor corresponds to the primary winding in the transformer and the rotor winding in induction motor corresponds to the secondary winding in the transformer.
- Both machines are works on the principle of electromagnetic induction.
- The equivalent circuit and vector diagram of both machines are almost the same.
- In the transformer, the electrical load connects at the secondary winding. If the load increase, the secondary current increases and therefore, the primary current is increase. The same thing happens with the induction motor. In that case, the mechanical load is connected with the rotor shaft and primary current replaced with the stator current and secondary current replaced with the rotor current. Now, if the mechanical load increase, the rotor current of induction motor increases and hence, the stator current increase.
Differences between Induction motor and Transformer
But there are some differences also.
- The Induction motor converts electrical power into mechanical power. In other words, the input of the induction motor is electrical energy and output is mechanical energy. In the case of a Transformer, input as well as output is electrical energy. The transformer uses to convert the voltage level of electrical power.
- In the case of the induction motor, the flux path is complete through the air gap. It means, between the stator winding and rotor winding, there is air gap. In the case of the transformer, the flux path is complete through the core. The core made up of low reluctance material. Therefore, the magnetizing current of the induction motor is about 30-40% of the rated current and the magnetizing current in the transformer is about 1-5% of the rated current.
- The transformer is a static device and an induction motor is a rotating device. Because of this reason, the efficiency of the induction motor is lower than the efficiency of the transformer.
- In case of the transformer, the both windings distribute around the periphery of the air gap. In case of a transformer, the winding is concentrated on a core. Therefore, the leakage reactance of the induction motor is large compared to the transformer.
- In an induction motor, the rotor voltage, reactance, and frequency are proportional to the slip s. Similarly, in transformer frequency is constant. For any value of slip s, rotor values are;
EMF per phase (E2’ = sE2)
Reactance per phase (X2’ = sX2)
Frequency (f’ = sf)
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