Class 2 (2nd Engineer) MET 📅 Dec 2024

Exam Question

(a) What is leakage flux as it applies to the iron-core transformer? How is it taken into account in the analysis of the transformer? (6)

(b) The following results were obtained on a 50 kVA transformer: open circuit test - primary voltage, 3300 V; secondary voltage, 415 V; primary power, 430 W. Short circuit test - primary voltage, 124V; primary current, 15.3 A; primary power, 525 W; secondary current, full load value. Calculate: (10)

(i) The efficiencies at full load and at half load for 0.7 power factor.

(ii) The voltage regulations for power factor 0.7 (i) lagging, (ii) leading

(iii) The secondary terminal voltages corresponding to (i) and (ii).

Reference Answer

In an iron-core transformer, when the primary winding is connected to a supply voltage, a current flows through the winding depending on the load and the winding resistance. This current generates a magnetic field , forming a magnetic north and south pole , thereby creating magnetic flux between them.
The magnetic flux consists of lines that ideally pass through the iron core and link both the primary and secondary windings . This mutual flux is responsible for the energy transfer from the primary to the secondary winding and is essential for transformer operation.
However, not all magnetic flux produced by the primary winding links to the secondary winding . Some of the magnetic lines spread into the surrounding air space and do not pass through the secondary coil. This portion of the magnetic flux is known as leakage flux .
Leakage Flux:

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