Advantages and Disadvantages of Induction Motor

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Key learnings:

Induction Motor Definition: An induction motor is defined as an electric motor that operates on alternating current (AC) and uses electromagnetic induction to generate motion.
Simple Construction: Induction motors have a simple and robust construction, making them reliable and low maintenance.
Advantages of Induction Motors: They include low cost, high efficiency, high starting torque, and safe operation without sparks.
Disadvantages of Induction Motors: They include lack of self-starting torque in single-phase motors, poor power factor at light loads, and difficulty in speed control.
Efficiency Range: Induction motors are highly efficient, with efficiency rates ranging from 85% to 97%.

Advantages of Induction Motor

An induction motor is an AC machine that produces torque by induction in the rotor. The main advantage of an induction motor is simple construction. Stator cores look similar on Synchronous motors and induction motors. Many wound-field synchronous machines use slip rings for the rotor field. Squirrel cage induction motors do not. Cage motors are also easier to maintain than DC Motors because they have no brushes.
A well-built induction motor is mechanically robust. Enclosure, cooling and ambient limits still have to match the site.
A squirrel-cage induction motor has no brushes, slip rings or commutators, so the machine is cheaper to build and to look after. Wound-rotor induction motors still use slip rings so that external resistance can be added to the rotor winding at start.
Without brushes, a cage motor has no brush sparking. Hazardous-area use still needs a certified enclosure.
Unlike many synchronous motors that need a separate starting method, a 3 phase induction motor is self-starting. Speed regulation on a fixed-frequency supply is tight. Overload capacity is reasonable. Starting torque depends on design class: Design B is modest, Design C or D is higher.
Full-load efficiency of industrial induction motors is often about 85% to 97%, with the high end on large premium-efficiency machines. Small motors sit lower.

A single phase induction motor with only a main winding has no self-starting torque. An auxiliary winding, capacitor or shaded poles is needed to start it. A 3 phase induction motor is self-starting.
At light load the power factor falls. Magnetising current needed to push flux across the air gap stays large while the load current is small. Their vector sum lags the voltage by about 75 to 80 degrees, so the power factor is low. Copper loss from that magnetising current then cuts light-load efficiency. Starting inrush is a separate issue.
Speed control of an induction motor on a fixed-frequency supply is limited because slip stays small over the load range. A variable-frequency drive is the usual modern method of varying speed.
Induction motors draw a large starting current, often several times full-load current. That locked-rotor current can dip the supply voltage at start, which is why plants sometimes group it with transformer Magnetising Inrush currents. Locked-rotor current lasts through the start; transformer inrush is a short flux-offset spike.
A general-purpose Design B cage motor has only modest starting torque, so it is a poor fit for loads that must break away against a heavy load. Wound-rotor machines and Design C or D cages are the usual choice for that duty.