B.TechSemester 42025-26Electrical Machines IBEE402

Electrical Machines I (BEE402) - AKTU Question Paper 2025-26

B.Tech · Semester 4 · Free PDF Download

This is the official AKTU Electrical Machines I Previous Year Question Paper for B.Tech Semester 4, academic session 2025-26. Published by Dr. A.P.J. Abdul Kalam Technical University (AKTU/UPTU), Lucknow. Free PDF download — no login required.

Course:B.Tech

Semester:Semester 4

Session:2025-26

University:AKTU / UPTU

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Questions Asked in 2025-26

Electrical Machines I (BEE402) — complete question paper · 70 marks · 3 Hours

Section AAttempt all questions in brief. 02 x 7 = 14

a
Define co-energy in an electromechanical system
b
What is armature reaction in DC machines?
c
A DC motor draws 20 A from a 220 V supply. Armature resistance is 0.5 Ω. Find back EMF
d
Differentiate between 3-point and 4-point starters
e
Draw phasor diagram of ideal transformer at no load condition
f
What is voltage regulation in a transformer?
g
Give conditions for three parallel operation of three phase transformer

Section BAttempt any three of the following: 07 x 3 = 21

a
Show that the field energy in a linear magnetic system is given by
b
Describe the process of commutation. Also explain its types and the methods to improve the commutation in DC machines
c
A 250 V dc shunt motor has an armature resistance of 0.5Ω and a field resistance of 250 Ω. When driving a constant torque load at 600 rpm, the motor draws 21 A. What will be the new speed of the motor if an additional 250 Ω resistance is inserted in the field circuit?
d
The maximum efficiency of a 100 kVA, 1100/440 V, 50 Hz transformer is 96%. This occurs at 75% of full load at 0.8 power factor lagging. Calculate the efficiency of transformer at half load and at 0.6 power factor lagging
e
Describe the 3-phase to 2-phase conversion in transformers with suitable diagram. Also, derive the expression for positioning of neural point

Section CAttempt any one part of the following: 07 x 1 = 07

a
Derive the expression for force and torque in a singly excited magnetic system
b
Explain the generation of EMF in electrical machines with cylindrical air gap. (SEM. IV) THEORY EXAMINATION 2025-26 ELECTRICAL MACHINES-I
a
Explain the armature reaction in DC generators using armature and field MMF waveforms. Describe the effects of armature reaction?
b
Discuss commutation and methods of improving commutation
a
A 230V DC series motor develops its rated output at 1500rpm while taking 20A. Armature and series field resistances are 0.3 Ω and 0.2 Ω respectively. Neglecting saturation, determine the resistance that must be added to obtain rated torque i) at starting and ii) at 1000 rpm
b
Explain Swinburne’s test to calculate no-load losses in a DC machine. State its limitations over Hopkinson’s test
a
Describe the construction, working, and advantages of autotransformers
b
A 200 kVA, 2000/440 V, 50 Hz, single phase transformer gave the following test results: O.C Test (hv) : 2 kV, 1.75 kW, 1.8 A S.C Test (lv) : 13 V, 1 kW, 300 A (i) Calculate the parameters of equivalent circuit as referred to H.V side (ii) Determine voltage regulation and efficiency at full-load, 0.8 power factor lagging
a
What is V-V connection? Show that the open delta connection has a kVA rating of 57.7% of the rating of the normal delta-delta connection
b
Explain Sumpner’s test in transformer with neat diagram

Question text is extracted from the official AKTU question paper PDF above. Hindi translations are omitted — every question is printed in English in the original paper. Last verified: 2026-08-23.

Repeated Questions — BEE402

Questions that appeared in more than one session, found by comparing 3 years of Electrical Machines I papers (2023-24, 2024-25, 2025-26)

Give conditions for three parallel operation of three phase transformer

Appeared in: 2023-24 · 2024-25 · 2025-26

The maximum efficiency of a 100 kVA, 1100/440 V, 50 Hz transformer is 96%. This occurs at 75% of full load at 0.8 power factor lagging. Calculate the efficiency of transformer at half load and at 0.6 power factor lagging

Appeared in: 2023-24 · 2024-25 · 2025-26

What is V-V connection? Show that the open delta connection has a kVA rating of 57.7% of the rating of the normal delta-delta connection

Appeared in: 2023-24 · 2024-25 · 2025-26

What is armature reaction in DC machines?