BE Computer Engineering (Pokhara University) Basic Electrical Engineering (PU, ELE 120) Question Paper 2079

For the network shown below, two voltage sources of 24 V and 12 V are connected through resistances. The 24 V source has a 4 Ω series resistor, the 12 V source has a 6 Ω series resistor, and a 8 Ω resistor connects the common node to ground.

(a) Using mesh (loop) analysis, write the loop equations and determine the current supplied by each source. (7)

(b) Verify your result for the current through the 8 Ω resistor using nodal analysis, and hence calculate the power dissipated in the 8 Ω resistor. (7)

(a) State Thevenin's theorem and explain the step-by-step procedure for obtaining the Thevenin equivalent of a linear two-terminal network. (4)

(b) A network consists of a 20 V source in series with a 5 Ω resistor, with a 10 Ω resistor connected in parallel across the output terminals A-B. Determine the Thevenin equivalent circuit as seen from terminals A-B. (5)

(c) Using the maximum power transfer theorem, find the value of load resistance connected across A-B that will absorb maximum power, and calculate that maximum power. (3)

(a) Distinguish between star (Y) and delta (Δ) connections in a three-phase system, deriving the relationship between line and phase values of voltage and current in each case. (6)

(b) A balanced three-phase star-connected load of impedance (8 + j6) Ω per phase is supplied from a 400 V, 50 Hz, three-phase line. Calculate the line current, power factor, total active power and total reactive power drawn by the load. (8)

(a) Derive the EMF equation of a single-phase transformer and explain the principle of operation on the basis of mutual induction. (5)

(b) A 50 kVA, 2200/220 V, 50 Hz single-phase transformer has a primary winding of 400 turns. Determine the number of secondary turns, the maximum flux in the core, and the full-load primary and secondary currents. (4)

(c) Draw the approximate equivalent circuit of a transformer referred to the primary side and label all parameters. (3)

A series RLC circuit having R = 10 Ω, L = 0.1 H and C = 100 μF is connected across a 230 V, 50 Hz supply. Calculate the impedance, the current drawn, the power factor and state whether the circuit is inductive or capacitive.

Define RMS value, average value and form factor of an alternating quantity. For a sinusoidal voltage v(t) = 311 sin(314t), determine its peak value, RMS value, frequency and form factor.

An iron ring of mean circumference 40 cm and cross-sectional area 5 cm² has a relative permeability of 1000. It is wound with a coil of 200 turns carrying a current of 2 A. Calculate the MMF, the reluctance of the magnetic circuit and the flux produced in the ring.

Derive the EMF equation of a DC generator. A 4-pole, lap-wound DC generator has 600 armature conductors and runs at 1000 rpm. If the flux per pole is 20 mWb, calculate the generated EMF.

(a) Explain the principle of operation of a DC motor and state the significance of back EMF. (3)

(b) A 220 V DC shunt motor has an armature resistance of 0.5 Ω and draws an armature current of 20 A. Calculate the back EMF developed by the motor. (3)

With a neat sketch, explain the construction and working principle of a Permanent Magnet Moving Coil (PMMC) instrument. State two advantages and two disadvantages of this type of instrument.

Describe, with a circuit diagram, the working of a Wheatstone bridge for the measurement of an unknown resistance. Derive the balance condition of the bridge.

State the Superposition theorem. Using it, determine the current flowing through a 5 Ω resistor in a circuit energised simultaneously by a 10 V voltage source and a 2 A current source, clearly showing the contribution of each source.

Explain the two-wattmeter method of measuring power in a three-phase circuit. How can the power factor of the load be determined from the two wattmeter readings?