(a) reduce the reluctance of the magnetic path.
(b) increase flux density in the air gap.
(c) permit mechanical clearance.
(d) avoid saturation of field.
Answer: (c) permit mechanical clearance.
Explanation:
CONCEPT: Electromechanical Energy Conversion
- An electromechanical
energy conversion device converts:
- Electrical
energy into mechanical energy, or
- Mechanical
energy into electrical energy.
- Energy
conversion takes place through a magnetic field, which acts as
a coupling medium.
- Magnetic
fields are preferred because their energy storage capacity is high.
- An
electromechanical energy converter consists of three main parts:
- Electrical
system
- Magnetic
coupling medium
- Mechanical
system
Role of the Air Gap
- A physical
air gap is provided between the stationary stator and
the rotating rotor.
- The
primary purpose of this air gap is to:
- Allow
free rotation of the rotor
- Prevent
physical contact, friction, and mechanical damage
- The
air gap ensures mechanical clearance for:
- Manufacturing
tolerances
- Shaft
misalignment
- Bearing
play
- Thermal
expansion during operation
Electrical vs Mechanical Considerations
- From
an electrical point of view, a smaller air gap is
desirable because:
- It
improves magnetic coupling
- It
increases efficiency
- From
a mechanical point of view, a minimum air gap is
essential to ensure safe and reliable operation.
- Hence,
the air gap size is a compromise between electrical performance
and mechanical safety.
Types of Electromechanical Energy Converters
- Gross-motion
devices:
- Electrical
motors
- Generators
- Incremental-motion
devices:
- Microphones
- Loudspeakers
- Electromagnetic
relays
- Electrical
measuring instruments
EXPLANATION
- Without
an air gap, the rotor would rub against the stator, causing:
- Excessive
friction
- Heating
- Mechanical
failure
- Therefore,
a small air gap is mandatory to permit mechanical
clearance while allowing magnetic energy transfer.
Final Answer
✅ Correct option: (c)
To permit mechanical clearance
✔️ Key One-Line Exam Statement
A small air gap is provided between stator and rotor to
allow mechanical clearance and safe rotation.