There are some of the advantages of induction motors compared to DC motors and synchronous motors. We will also discuss disadvantages of induction motors compared to other motors. An induction motor is the best choice for industrial applications. The AC power is used in generation, transmission and distribution. Therefore, it is easy to use an induction motor which works on the principle of electromagnetic induction.
Almost 65 % of the machines used in the industries were 3 phase induction motor. However, nowadays application of the induction motor escalated, and about 85 % machines in the industries are induction motor. The use of induction motor increased because nowadays it is very easy to use motor with VFD for speed control.
Earlier for speed control, DC motors were used in industries. Now, most of the industries are using induction motor with variable frequency drive (VFD) for speed control application. There are two types of induction motor: Squirrel cage induction motor and slip ring /wound rotor induction motor. The use of the slip ring motor is almost obsolete because it requires more maintenance.
The squirrel cage motor with VFD has taken the place of slip ring induction motor. Now, we will discuss about the advantages and disadvantages of induction motor over other types of motor.
Advantages of Induction Motor
- The most important feature of an induction motor is that it is very simple in construction. The stator construction of the induction motor is similar to the construction of stator of the Synchronous motor. The induction motor rotor does not have slip ring, the rotor conductors internally short circuited at the end rings. However, a synchronous motor has a slip ring to feed DC supply to its exciter. Thus, squirrel cage motor is better than synchronous motor because it requires very less maintenance.It has low maintenance cost.
- A slip ring motor or wound rotor motor has slip rings and, the slip ring and carbon brushes require frequent maintenance. The squirrel cage induction motor does not have slip rings and brushes and, therefore it requires very less maintenance.
- The induction motor is robust in construction, and its performance does not affect with environmental conditions.
- A squirrel cage induction motor has few number of parts as compared to DC motor, synchronous motor and slip ring induction motor.The Squirrel cage induction motor does not have slip rings, carbon brushes and commutator, therefore the cost of the Squirrel cage induction motor is low as compared to other types of motor.However, a slip ring or Wound rotor type induction motor, synchronous motor and DC motor have slip rings, carbon brushes and commutator, and because of increased parts procurement cost and operating cost both are more compared to squirrel cage induction motor.
- The Squirrel cage induction motor does not have slip rings and carbon brushes. The sparking between the slip ring and brushes may happen in the case of slip ring or DC motor. In the case of Squirrel cage induction motor sparking is absent, therefore the motor can be operated in hazardous conditions like polluted & explosive environment.
- The three phase induction motor has a reasonable starting torque, fair speed regulation. The motor is almost a constant speed motor and it gives fair speed regulation. The motor has reasonable overload capacity.
- The efficiency of an induction motor varies between 85 to 98 %.
- 3 phase induction motor is self starting type motor and no additional starting method required unlike synchronous motor.
- Squirrel cage induction motor is almost constant speed motor and its speed slightly changes with change in loading.
All these above mentioned advantages make induction motor the most popular and important for use in domestic and industrial application.
Disadvantages of Induction Motor
- A single phase induction motor can not generate the rotating magnetic field and hence it is not self starting motor. Some added auxiliaries make the single phase induction motor self starting.
- The induction motor takes high reactive power at no load operation and its power factor is very low at no load or light load. At start,the motor draws a very large magnetizing current and it cause low power factor. The lower power factor cause higher I2R loss, and the system efficiency gets poor with lower power factor. The power factor improves with higher loading. Additionally, power factor compensation capacitor bank can be used for power factor improvement.
- The induction motor is almost a constant speed motor, and the speed control of induction motor is very difficult to attain because there is slight change in the speed for the entire loading range. However, the induction motor is most suitable for speed control if used with variable frequency drives
- The induction motor draws large magnetizing current at start. This can cause system voltage drop if power system rating is not proper. Thus, it affects the system voltage stability.
- The starting torque of the Squirrel cage induction motor is low and hence it is not suitable for the applications which require high starting torque. However, squirrel cage induction motor with VFD can deliver higher starting torque at start. The other option of getting higher starting torque is use of slip ring induction motor. A DC motor also provides highest starting torque among squirrel cage and slip ring induction motor.
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