Hall Ticket No:
Question Paper Code: A3213
VARDHAMAN COLLEGE OF ENGINEERING
(AUTONOMOUS) B. Tech IV Semester Regular/Supplementary Examinations, May 2018
(Regulations: VCE-R15) PRINCIPLES OF ELECTRICAL ENGINEERING
(Electronics and Communication Engineering) Date: 15 May, 2018 FN
Time: 3 hours
Max Marks: 75
Answer ONE question from each Unit
All Questions Carry Equal Marks
Unit I
1.
State faraday's laws of Electromagnetic Induction. Derive an expression for the value of induced EMF.
6M
i. A coil of 500 turns is linked by a flux of 0.4mWb. If the flux is reversed in 0.01sec, find the EMF induced in the coil
ii. If a coil of resistance 100Ω is placed in a magnetic field of 1mWb. The coil has 100 turns and a galvanometer of 400Ω resistance is connected in series with it. Find the average EMF and current if the coil is moved in 0.01sec from the given field to a field of strength 0.2mWb
9M
2.
Calculate the total inductance of two coils when joined in series aiding.
7M
The number of turns in a coil is 250. When a current of a 2A flows in this coil. The flux in the coils 0.3mWb when this current reduces to zero in 2 millisecond. The voltage in the coil lying in the vicinity of the coil is 63.75 Volts. If the co-efficient of coupling between the coils is 0.85, find self-inductances of the two coils, mutual inductance and the number of turns in the secondary coil.
8M
Unit II
3.
Derive an expression for current in RL series circuit for DC excitation.
6M
In the circuit diagram, steady state is reached with the switch closed. The switch is opened at t=0. Obtain expressions for and VL(t).
Fig.1
9M
4.
Derive an expression for current in RC Series Circuit for DC excitation.
7M
In the network, the switch is moved from 1 to 2 at t=0. Determine
Fig.2
8M
Unit III
5.
Explain speed control methods of DC shunt motor.
6M
Derive the emf equation of a dc generator. A 2 pole wave wound generator has 51 slots and 24conductors/slot. If the flux per pole is 0.01Wb, determine the speed at which the armature be driven to give an induced emf of 220V.
9M
Cont…2
2
6.
Explain principle of operation of DC machines with relevant diagrams.
8M
The current drawn from the mains by a 220V, DC shunt motor is 3A on no load. The armature and field resistance are respectively 0.5Ωand 200Ω. If the line current on load is 51A at a speed of 1200rpm, find the no load speed.
7M
Unit IV
7.
Explain the working principle of a single phase transformer with constructional features.
8M
A 150 KVA single phase transformer working at unity power factor has efficiency of 96% both at 70% full load and at full load. Find the load at which maximum efficiency occurs and also the value of maximum efficiency.
7M
8.
Explain the OC test of a transformer.
8M
The efficiency of a 400kVA single phase transformer is 98.77% when delivering full load at 0.8 p.f. and 99.13% at half load and unity power factor. Calculate iron losses and full load copper losses.
7M
Unit V
9.
Explain slip torque characteristics of a 3-phase Induction motor.
7M
Compare slip ring and squirrel cage induction motors with necessary figures.
8M
10.
Derive an expression for the torque developed by an IM under running condition. When does it achieve maximum value?
8M
The power input to the rotor of a 440V, 50Hz 3 phase, 12 pole IM is 75W. The rotor EMF has a frequency of 2Hz. Calculate:
i. Slip
ii. Rotor speed
iii. Rotor Copper loss
7M