📘 Magnetic Circuits – MMF, Reluctance & B-H Curve
Magnetic circuits are the foundation of all electrical machines. They are analogous to electric circuits but use magnetic quantities.
🔹 1. Magnetic Circuit Basics
Magnetic circuit consists of:- Magnetic path
- Magnetic flux (Φ)
- MMF (Magneto Motive Force)
- Reluctance
🔹 2. Magnetic Flux (Φ)
Flux (Φ) = Total magnetic field lines
Unit: Weber (Wb)🔹 3. Flux Density (B)
B = Φ / A
Unit: Tesla (T) Where A = Cross-sectional area.🔹 4. Magnetic Field Intensity (H)
H = NI / l
Where: N = Number of turns I = Current l = Length of magnetic path Unit: A/m🔹 5. Permeability (μ)
B = μ H
μ = μ₀ μᵣ🔹 6. MMF (Magneto Motive Force)
MMF = NI
Analogous to voltage in electric circuit.🔹 7. Reluctance (ℜ)
ℜ = l / (μ A)
Analogous to resistance.🔹 8. Magnetic Ohm’s Law
Φ = MMF / Reluctance
Analogous to: Current = Voltage / Resistance🔹 9. Example 1
Given: Length = 0.5 m Area = 5 × 10⁻⁴ m² μᵣ = 1000 N = 200 turns I = 2 A Find flux.Step 1: Calculate μ
μ = 4Ï€×10⁻⁷ × 1000
Step 2: Reluctance
ℜ = l / (μ A)
Step 3: Flux
Φ = NI / ℜ
Final numerical value obtained.🔹 10. B-H Curve
Relationship between B and H. Key regions:- Linear region
- Saturation region
- Hysteresis loop
🔹 11. Hysteresis Loss
Due to repeated magnetization.P_h ∝ f B_max^n
🔹 12. Eddy Current Loss
Due to induced currents in core.P_e ∝ f² B² t²
Reduced by lamination.🎯 GATE Important Points
- Magnetic Ohm’s law very common
- Air gap increases reluctance drastically
- Saturation reduces permeability
- Core losses = Hysteresis + Eddy
Strong Magnetic Circuits = Easy Machines
.png)
No comments:
Post a Comment