Electrical Machines and Applications- I — Winter 2025

State the principle of Electromechanical Energy Conversion. Also, state the formula for the energy stored in a magnetic field system.

Explain the concept of Co-energy and derive the expression for the magnetic force in a singly excited linear magnetic system using the energy stored in the field.

With the help of a neat diagram, explain the construction, working principle, and applications of a PMDC (Permanent Magnet DC) Motor.

Draw the neat cross-sectional view of a DC machine and list the function of any four major parts, such as yoke, pole shoe, and commutator.

Explain the effect of Armature Reaction in a DC Generator and describe the function of a Compensating Winding used to counter its effects.

A 4-pole, wave-connected DC generator has 60 slots with 10 conductors per slot. The armature resistance is 0.1 Ω. When driven at 1200 rpm, the generator supplies a load of 10 Ω resistance at 200 V. Find (i) the total armature current (Ia) and (ii) the flux per pole (Φ). Neglect shunt field current for approximation.

A 230 V DC series motor draws an armature current of 40 Aand runs at 900 rpm. The armature resistance and series field resistance are 0.1 Ω and 0.2 Ω, respectively. Assuming the flux is reduced by 50% due to saturation when the current increases from 40 Ato 60 A, calculate the new speed when the motor draws 60 A.

Define All-day Efficiency for a transformer. Why is it more significant for a distribution transformer than a power transformer?

Draw the Phasor Diagram of a single-phase transformer operating at a lagging power factor load. Clearly show the primary and secondary voltages and currents.

The maximum efficiency of a 100 kVA single-phase transformer is 98% and occurs at 80% of full load at unity power factor. Calculate the (i) iron loss and (ii) full-load copper loss of the transformer.

Derive the EMF equation of single-phase transformer. Page 1 of

Draw the vector diagram of single-phase transformer considering the effect of winding resistance and magnetic leakage for capacitive load and explain in brief.

A 20 kVA, 2000/200 Vsingle-phase transformer has 66 turns in the secondary winding. If the core cross-sectional area is 40 cm2, calculate (i) the number of turns in the primary winding, (ii) the maximum flux density in the core, and (iii) the full- load primary current. Assume 50 Hz supply.

List and briefly describe the essential conditions that must be fulfilled for the successful parallel operation of two single-phase transformers.

Explain the principle of operation and draw the schematic diagram of a 3-point starter used for a DC shunt motor.

With the help of necessary diagrams, explain the Y−Δ (Star-Delta) and Δ−Y (Delta- Star) connection of a three-phase transformer. State one main application for each connection.

Explain Core type and Shell type single-phase transformer.

Explain the principle of operation and draw the schematic diagram of a 4-point starter used for a DC shunt motor.

With the help of necessary diagrams, explain the connection of a Scott-connected transformer. State the main purpose of this connection.

Why is a Δ−Δ connected three-phase transformer bank converted to an open-delta (V−V) connection? Calculate the power rating of the open-delta bank if the original rating was 100 kVA.

With the help of neat sketches, explain the working and torque-speed characteristics of a Variable Reluctance Stepper Motor.

Describe the concept of reactance voltage during commutation in a DC machine. Explain the role of interpoles in improving commutation.

Amagnetic field system has a coil with a current of 5 Aand an inductance of 0.1 H. The air gap length is 0.5 mm. Calculate the magnetic force developed in the system.

Draw and Explain Power Flow Diagram for DC Generator and DC Motor.

Define Generator. Explain the Classification of DC Generator with diagram. Derive EMF equation of DC Generator. Page 2 of