Question

What is the self excited induction motor?
How it is work?
What is the limitation of self-excited?
When is the advantages and disadvantages of self-excited induction motor?
What is the c\Cs curve of self-excited induction motor?

Answer 1

1)  

When a suitable capacitance is connected across the stator winding of an induction machine, self-excitation may occur under favorable conditions, and a machine operating in this mode is called a self-excited induction motor.

2)  Working of self excited induction motor

* In an induction motor, the rotor rotates because of slip (i.e. relative velocity between the rotating magnetic field and the rotor). Rotor tries to catch up the synchronously rotating field of the stator but never succeeds. If rotor catches up the synchronous speed, the relative velocity will be zero, and hence rotor will experience no torque.

* A capacitor bank can be connected across the stator terminals to supply reactive power to the machine as well as to the load. When the rotor is rotated at an enough speed, a small voltage is generated across the stator terminals due to residual magnetism.

3) Limitation of self-excited

Dependency of the output voltage and frequency of the isolated self-excited induction motor on the speed, load, and terminal capacitance causes certain limitations on its performance.

* It is found that the machine operates only in certain element ranges and that all generated currents and voltages are bounded.

* It is also shown that a combination of these elements exists that is optimal for maximum power generation.

4) Advantages and disadvantages of self-excited induction motor?

Advantages:

* The advantages of induction motors are simple construction, less expensive, robustness, high efficiency, and satisfactory drive characteristics for most applications.

Disadvantages:

* Induction motors must operate at lagging power factors, meaning that they draw a considerable amount of reactive power from the power supply.

* Moreover, speed control is difficult and expensive to achieve.

* Before the advent of power electronics, induction motors were used mainly for constant-speed applications.