Test: Reluctance - Electrical Engineering (EE) MCQ

The reciprocal of reactance is permeance. It is the ability of a material to allow the passage of magnetic lines of flux.

Reluctance is inversely proportional to the area of cross section of the material hence as area increases, reluctance decreases.

Resistance is the opposition to the flow of charge, similarly reluctance is the opposition to the flow of magnetic flux.

Reluctance is inversely proportional to the magnetic flux density, hence as magnetic flux density increases, reluctance decreases.

The formula for reluctance is:
S = l/µ₀ µ_r*A.
From the formula, we can see that reluctance is directly proportional to the length of the material.

Reluctance is directly proportional to the length of the material hence as length increases, reluctance also increases.

Reluctance is magnetomotive force per unit flux,
So unit of reluctance = unit of MMF / unit of magnetic flux = A/Wb.

Reluctance is directly proportional to the strength of the magnetic field, hence as the strength of magnetic field increases, the reluctance increases.

We know that:
F = ϕ*S
Substituting the given values from the question:
S = 2A/Wb.

Switched reluctance motor (SRM):

• The switched reluctance motor is a doubly salient, singly excited motor that produces torque at synchronous speed.
• It has salient poles on both the rotor and the stator, but only one member (usually the stator) carries windings.
• The rotor has no windings; magnet or cage windings but is built up from stacks of salient pole laminations.
• It is a stepper motor with closed-loop control and with rotor position sensor.
• It is designed for high speed and the closed loop system is necessary.
• It is normally necessary to use a rotor position sensor for communication and speed feedback. The turning ON and OFF operation of the various devices of the power semiconductor switching circuit are influenced by signals obtained from the rotor position sensor.

Advantages:

• Construction is simple and robust
• It requires less maintenance
• Its overall efficiency is better
• It is a flexible control driving motor as motoring mode and generating mode of operations of the machine can be easily achieved.