Basic Electrical Engineering (BEE) - Jun 2015

First Year Engineering (Semester 1)

TOTAL MARKS:
TOTAL TIME: HOURS

Answer any one question from Q1 and Q2

1 (a) If a coil of 150 turns is linked with a flux of 0.01 Wb when carrying a current of 10 A, then calculate the induced emf.
i) if this current is uniformly reversed in 0.1 second.
(ii) if this current is interrupted in 0.05 second.(6 marks) 1 (b) Define insulation resistance and obtain an expression for insulation resistance of a single core cable.(6 marks) 2 (a) Explain what do you mean by statically induced EMF and dynamically induced EMF(6 marks) 2 (b) A coil of insulated copper wire has a resistance of 150 Ω at 20°C. When the coil is connected across a 240 V supply, the current after several hours is 1.25 A. Calculate the temperature of the coil, assuming the temp. co-efficient of resistance of 20°C to be 0.0039 per °C.(6 marks)

Answer any one question from Q3 and Q4

3 (a) Derive an EMF equation of 1-ph transformer.(6 marks) 3 (b) Derive an expression for instantaneous current and power consumed when voltage of V = V_m sin ( t) is applied to pure inductance alone. Also draw the phasor diagram.(6 marks) 4 (a) A single phase 4 kVA transformer has 400 turns on its primary and 1000 secondary turns. The net cross-sectional area of the core is 60 cm². When the primary winding is connected to 500 V, 50 Hz supply, calculate:
i) the max. value of flux density in the core
(ii) the voltage induced in the secondary winding and
(iii) the secondary full load current.(6 marks) 4 (b) The expression of the alternating current is given by i = 5.48 sin Ωt:
Calculate:
(i) the average value
(ii) RMS value of the current
(iii) power consumed if the current is passed through a resistance of 10 Ω.(6 marks)

Answer any one question from Q5 and Q6

5 (a) What is admittance of an AC circuit ? What are its two components? State units of these quantities. How the admittance is expressed in rectangular and polar form?(6 marks) 5 (b) An impedance Z₁ = (100 + j0) Ω is connected in series with another impedance Z₂ = (50 + j80) . The circuit is connected to a single phase 230 V, 50 Hz supply. Calculate:
i) current drawn by the circuit
(ii) power consumed by whole circuit
(iii) circuit power factor.(7 marks) 6 (a) Draw and explain phasor diagram of an RLC series circuit, When :
i) X_C > X_L.
ii) X_C < X_L
iii) X_C = X_L(7 marks) 6 (b) A delta connected balanced load across a 400 V 3-phase supply consist of three identical impedances, each equal to (15+j12) Ω Find the line current, active power and reactive power.(6 marks)

Answer any one question from Q7 and Q8

7 (a) State and explain Superposition Theorem.(6 marks) 7 (b) Using Kirchhoff's Law, determine the current flowing through 6 &Omelga; resistance.

(7 marks) 8 (a) Derive the expressions to convert delta connected resistances into equivalent star circuit.(6 marks) 8 (b) Using Thevenin's Theorem, determine the value of current flowing through 6 Ω resistance.

(7 marks)