Diploma-Diploma Electrical Engineering (DEE) 1st Sem Basic of Electrical Engineering(Gujarat Technological University-2013)
Thursday, 29 August 2013 06:44anudouglas
GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA - SEMESTER – I • EXAMINATION – WINTER 2012
Subject code: 3320901 Date: 07-01-2013
Subject Name: Basic of Electrical Engineering
Time: 10.30 am – 01.00 pm Total Marks: 70
Instructions:
1. Attempt any five questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. English version is Authentic.
Q.1 Answer the following questions in brief. (Any seven) 14
(1) Define the leakage factor. State its value for electrical machines.
(2) State the conditions for production of dynamically induced emf. Also state the
equation to find dynamically induced emf. (3)
Define coefficient of coupling. Two coupled coils of self inductances 0.8H & 0.2H have a coefficient of coupling is 0.9.Find the mutual inductance. (4)
The rms value of an alternative current is 50A. Find its max value & average value.(5)
Explain necessity of earthing. (6)
Define transformation ratio of a transformer. State its value for step up and
for step down transformer. (7)
Why single phase induction motor is not self starting? (8)
State various types of 3-φ induction motor & their applications. (9)
Write the full form of following.
(i) MCB (ii) HRC (iii) ELCB (iv) RCCB (10)
List any four precautions to be followed while carrying out electrical work.
Q.2 (a) Derive emf equation of transformer. 05
(b) Explain plate earthing with diagram. 05
(c) Give difference between single phase core type and shell type transformer. 04
OR
(a) A 50 kVA 1100/440 V, 50Hz, single phase transformer has iron loss of 1.5 kW and full load copper loss of 2 kW. Find efficiency at (i) full laod 0.8 lagging p.f.. (ii) half full load unity power factor. 05
(b) Explain the construction & working of MCB. 05
(c) Compare two winding transformer with auto transformer. 04
Q.3 (a) Explain direct on line starter with circuit diagram. 05
(b) Explain working of capacitor start capacitor run type induction motor using one capacitor. 05
(c) Prove that in pure inductive circuit current is lagging behind the voltage by
90° . 04
OR
(a) Explain star-delta starter with circuit diagram. 05
(b) Explain working of resistance start induction run type induction motor. 05
(c) Prove that in pure capacitive circuit current is leading the voltage by 90°. 04 Q.4 (a) (i) Explain Faraday’s low of electromagnetic induction. 04
(ii) Calculate the inductance of the coil having 400 turns linked with a flux of 10 mwb,when it carries a current of 10A. Also calculate the self induced emf if this current is reduced to a value of 2A uniformly in 20 ms. 03
OR
(i) State the relation between phase voltage and line voltage, phase current and line current for (i) star connection (ii) delta connection. Also write down equation of power for both type of connection. 04
(ii) Electrical power consumption per day in a house is as follow find the energy cost for 30 days @ Rs. 5.0 per unit (i) 3 tube lights each of 55 W for 5 hours (ii) 2000 W heater for 0.5 hour (iii) 3 fans each of 60W for 8 hour 03
(b) Explain R-L-C series circuit with necessary equations. 07
Q.5 (a) A 10 ohms resistor and a 20 mH inductor are connected in series across a 230V, 50 Hz supply. Find the circuit reactance, impedance, current, active power, reactive power, apparent power and power factor. 07
(b) Explain various losses in transformer. 04
(c) What is hysteresis loop ? Explain importance of hysteresis loop. 03
| Earning: ₹ 6.50/- |
