Transformer loading and ampere-turn balance: In a transformer, if the secondary current (and thus the secondary ampere-turns and magnetic field) increases due to increased load, what happens to the primary current Ip?

Introduction / Context:
Transformers operate by mutual induction and the balance of ampere-turns. The primary and secondary currents interact via the core flux. Understanding how primary current responds to secondary loading is vital for interpreting input current measurements and selecting protective devices.

Given Data / Assumptions:

• Ideal transformer approximation (tight coupling, negligible leakage and copper loss).
• Primary is fed by a constant-voltage AC source.
• Secondary load current increases.

Concept / Approach:
Core flux is set primarily by applied primary voltage and frequency. When secondary load current increases, its ampere-turns produce a demagnetizing component of flux that would reduce net core flux. The transformer responds by drawing additional primary current to supply the load’s power and to maintain the original core flux (ampere-turns balance). Therefore, increased secondary current results in increased primary current according to the turns ratio and power balance.

Step-by-Step Solution:
Primary voltage sets a near-constant magnetizing flux in the core.Secondary load current produces opposing ampere-turns (demagnetizing).To keep net flux near constant, primary draws extra current so Np * Ip approximately cancels Ns * Is (plus magnetizing current).Hence, Ip increases as secondary load increases.

Verification / Alternative check:
Power balance: P_primary ≈ P_secondary (neglecting losses). If secondary power rises, primary apparent power and hence current must rise.

Why Other Options Are Wrong:
Ip canceled or remains the same: contradict power and ampere-turn balance.Ip decreases: opposite of observed behavior under increased load.

Common Pitfalls:
Assuming core flux varies widely with load; in practice, with constant applied voltage, flux stays nearly constant while currents adjust.

Final Answer:
Ip will increase.