Class 2 (2nd Engineer) MET 📅 Jul 2025

Exam Question

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

(b) Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates a maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find: (10)

(i) the r.m.s. value of the resultant voltage and

(ii) the 'breadth factor'. Using the basis of this problem, give

(iii) reason why are the factors which determine the synchronous speed of a motor?

Reference Answer

(a) 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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