## Basic Electrical & Electronics Engg - May 2015

### First Year Engineering (Semester 1)

TOTAL MARKS: 80

TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.

(2) Attempt any **three** from the remaining questions.

(3) Assume data if required.

(4) Figures to the right indicate full marks.
**1 (a)** Convert the star circuit into its equivalent delta circuit.

(3 marks)
**1 (b)** For the given circuit find the Norton equivalent between point A and B.

(3 marks)
**1 (c)** Draw an a.c. waveform indicate there on and explain (i) instantaneous value, (ii) peak value and (iii) time period for one cycle of the alternating quality.(3 marks)
**1 (d)** Differentiate between series and parallel resonance wth respect to

i) Impedance at resonance

ii) Current at resonance

iii) Magnification factor(3 marks)
**1 (e)** Draw the phasor diagram for 3 phase delta connected load with a lagging power factor. Indicate line and phase voltage and currents.(2 marks)
**1 (f)** Derive the emf equation for a single phase transformer.(4 marks)
**1 (g)** Draw a neat circuit diagram for a full wave bridge rectifier using 4 diodes and the corresponding inputs and output waveforms for voltage.(2 marks)
**2 (a)** Find the current through 1 ? resistance using Mesh Analysis.

(6 marks)
**2 (b)** A coil having a resistance of 10? and an inductance of 40 mH is connected to a 200V, 50 Hz supply. Calculate the impedance of the coil, current, power factor and power consumed.(8 marks)
**2 (c)** Draw the phasor diagram of a transformer on no load and explain the various currents and voltage in it.(6 marks)
**3 (a)** Three similar coils each having a resistance of 10? and inductance of 0.04 H are connected in star across a 3 phase, 50Hz, 200V supply. Calculate the line current, total power absorbed, reactive volt amperes and total volt amperes.(8 marks)
**3 (b)** With the help of a neat diagram explain how short circuit test is conducted on a single phase transformer.(6 marks)
**3 (c)** Draw the circuit diagram of a full wave centre tapped rectifier with capacitor filter and the corresponding input and output waveforms.(2 marks)
**3 (d)** With the help of a neat diagram explain the output characteristics of an NPN transistor in common emitter configuration.(4 marks)
**4 (a)** Using source transformation find the current flowing through the 8? resistance

(7 marks)
**4 (b)** Find the rms value for the given waveform.

(5 marks)
**4 (c)** Two wattemeters are used to measure power in a 3? balanced star connected load using the two wattmeter method. The readings of the 2 wattmeters are 500W and 2500W respectively. Calculate the total power consumed by the 3? load and the power factor.(4 marks)
**4 (d)** With the help of a neat circuit diagram and input and output waveform explain the working of a half wave rectifier.(4 marks)
**5 (a)** Find the current through 8? resistance using Thevenins theorem.

(8 marks)
**5 (b)** A resistance of 10? and a pure coil of inductance 31.8 mH are connected in parallel across 200V, 50 Hz supply. Find the total current and power factor.(4 marks)
**5 (c)** A 5KVA, 1000/200V, 50Hz, single phase transformer gave the following test results.

OC test (hv side): 1000V 0.24A 90W

SC test (hv) side: 50V 5A 110W

Calculate the equivalent circuit parameters of the transformer and draw the equivalent circuit diagram.(8 marks)
**6 (a)** Find the value of current flowing through the 5? resistance using superposition theorem.

(7 marks)
**6 (b)** A series KLC circuit has the following parameter value: R=10?, L=0.014H, C=100?F Compute the resonant frequency, quality factor. Bandwidth, lower cut-off frequency and upper cut-off frequency.(7 marks)
**6 (c)** With the help of a neat circuit diagram and phasor diagram explain the 2-wattmeter method to measure power in a 3? balanced star connected load.(6 marks)