In a transformer core, what effect does adding an air gap have on inductance and leakage inductance?

In a transformer core, what effect does adding an air gap have on inductance and leakage inductance?

• A. Inductance decreases; leakage inductance increases; reluctance increases.
• B. Inductance increases; leakage inductance decreases; reluctance decreases.
• C. Inductance unchanged; leakage unchanged; reluctance unchanged.
• D. Inductance decreases; leakage inductance decreases; reluctance increases.

Answer: (B)

When you insert an air gap into the magnetic path, the reluctance of the core rises because the gap is a high-reluctance region (air has a much lower permeability than iron). Inductance is inversely related to reluctance for a given number of turns, so the magnetizing inductance drops as the gap increases. At the same time, coupling between the windings weakens. The flux is less tightly tied to both windings, so more flux leaks away from linking the secondary. That means leakage inductance tends to rise when an air gap is present. Reluctance increases due to the gap, inductance decreases because of the higher reluctance, and leakage inductance increases because coupling worsens.

When you insert an air gap into the magnetic path, the reluctance of the core rises because the gap is a high-reluctance region (air has a much lower permeability than iron). Inductance is inversely related to reluctance for a given number of turns, so the magnetizing inductance drops as the gap increases.

At the same time, coupling between the windings weakens. The flux is less tightly tied to both windings, so more flux leaks away from linking the secondary. That means leakage inductance tends to rise when an air gap is present.

Reluctance increases due to the gap, inductance decreases because of the higher reluctance, and leakage inductance increases because coupling worsens.