Elements of Electrical Engineering — Winter 2018

Derive an expression for temperature coefficient at temperature t,  /(1t).Where notation have usual meaning. t 0 0

Derive an expression for calculating equivalent start to delta transformation.

The resistance of a certain length of wire is 4.6 Ω at 20◦ Cand 5.68 Ω at 80◦ C. Determine (i) temperature co-efficient of resistance of the material of wire at 0◦ C (ii) resistance of wire at 60◦C.

Find the effective resistance of the network shown in Figure I. Fig. I

Compare electric circuit with magnetic circuit.

Two metal plates of area 100 cm2 are separated by a dielectric of a 2 mm having a relative permittivity of 5.When a dc voltage of 500 Vis applied across the capacitor plates, find (i) capacitance (ii) charge on the capacitor (iii) electrical field strength and (iv) electric flux density.

Define capacitance. Derive an expression for the total capacitance of a group of capacitance when (i) they are connected in series (ii) they are connected in parallel.

Two coils having 100 and 1000 turns respectively have common magnetic circuit of 25 cm diameter and 625 cm2 cross-section and a constant relative permeability of 2000.Calculate,

Self inductance of both the coils (ii) Mutual inductance between them if the co-efficient of coupling is 0.5.1

Prove that current in purely inductive circuit lags its voltage by 90◦ and average power consumption in pure inductor is zero.

An air-cored choke coil takes a current of 3 Aand dissipates 200 W, when connected to 200 V, 50 Hz supply. In another similar coil, current is 3 Aand power is 270 Wunder the same conditions. Calculate the (i) current taken (ii) power factor (iii) total power absorbed when two coils are connected in series to the same supply.

State relation between line voltage and phase value of voltage and current for

Balanced star connected load. (ii) Balanced delta connected load.

Explain variation of wattmeter readings for 3-phase power measurement by two watt method as power factor takes values of unity, 0.5, between 0.5 and 0 and 0.

Explain charging of battery from AC supply with schematic diagram.

Explain construction of cable. Explain each part and its importance.