(a) eddy current loss
(b) hysteresis loss
(c) both eddy current and hysteresis loss
(d) weight of the stator
(e) windage and frictional losses
Answer: (a) eddy current loss
Explanation:
CONCEPT: Stator Core in Induction Motor
- The stator is the stationary part of the induction motor.
- It carries three-phase windings supplied with AC.
- Alternating current produces an alternating magnetic flux in the stator core.
- This changing flux induces circulating currents in the core material.
These currents are called:
👉 Eddy currents
PROBLEM: Eddy Current Loss
- Eddy currents flow in closed loops inside the iron core.
- They produce heat due to resistance of iron.
- This causes:
❌ Power loss
❌ Heating
❌ Reduced efficiency
❌ Reduced life of insulation
This loss is called:
👉 Eddy current loss
SOLUTION: Lamination of Core
- To reduce eddy currents, the stator core is laminated.
- It is made of thin steel sheets (stampings).
- Thickness ≈ 0.4 to 0.5 mm
- Each sheet is insulated by varnish coating.
- These sheets are stacked together.
This construction is called:
👉 Laminated Core
HOW LAMINATION REDUCES EDDY CURRENT LOSS
- Insulation between sheets increases resistance.
- Eddy current paths are broken.
- Circulating currents are reduced.
- Heat generation decreases.
- Power loss is minimized.
Therefore:
✔ Eddy current loss is reduced.
ROLE OF SILICON STEEL
- Stampings are made of silicon steel.
- Silicon steel has:
✔ High permeability
✔ Low hysteresis loss
- This reduces hysteresis loss.
But:
👉 Lamination mainly reduces eddy current loss.
PARTS OF STATOR
The stator consists of:
- Stator Frame
- Stator Core
- Stator Winding
1. Stator Frame
- Outer body
- Made of cast iron / steel
- Provides mechanical support
- Maintains air gap
2. Stator Core
- Laminated silicon steel
- Carries alternating flux
- Reduces eddy current loss
3. Stator Winding
- Three-phase copper coils
- Placed in slots
- Connected in star or delta
- Supplied with 3-phase AC
ADDITIONAL INFORMATION
Air Gap
- Air gap = distance between stator and rotor.
- Affects efficiency and torque.
- Must be uniform.
Commutator
- Used only in DC machines.
- Not present in induction motors.
WHY OTHER OPTIONS ARE INCORRECT
(b) Hysteresis Loss ❌
- Hysteresis loss is reduced mainly by silicon steel.
- Lamination has minor effect.
(c) Copper Loss ❌
- Copper loss occurs in windings.
- Depends on current and resistance.
- Not related to lamination.
(d) Mechanical Loss ❌
- Mechanical losses are due to:
- Friction
- Windage
- Lamination does not affect them.
IMPORTANT EXAM POINTS ⭐
One-Line Facts
✔ Lamination reduces eddy current loss
✔ Silicon steel reduces hysteresis loss
✔ Thin insulated sheets are used
✔ Thickness ≈ 0.5 mm
MCQ Tip
Q: Why stator core is laminated?
👉 To reduce eddy current loss
FINAL CONCLUSION ⭐
The stator core of a 3-phase induction motor is laminated to restrict the flow of eddy currents by breaking their paths. This reduces heat generation, minimizes power loss, and improves motor efficiency. Hence, the primary purpose of lamination is to reduce eddy current loss.
KEY ONE-LINE EXAM STATEMENT ⭐
Lamination of stator core is done mainly to reduce eddy current loss and improve efficiency.