Subject 2018 Question Paper — Government College of Engineering and T…

Instructions

• Attempt five questions in all selecting at least two questions from each Section.
• Assume data wherever necessary.
• Each question carries 20 marks.

Questions

Section - A

• Q1. (a) Draw single line diagram of a typical power system. Locate various sections of it and mention these on typical voltages of generation, transmission and distribution. (b) A single phase A, C distributor AB is fed from end a and has a total impedance of $(0.2 + j 0.3)$ ohm. At the far end, the voltage $V_B = 240\text{V}$ and the current is $100\text{A}$ at a p.f. of $0.8$ lagging. At the mid - point M, a current of $100\text{a}$ is tapped at a p.f. of $0.6$ lagging with reference to the voltage $V_m$ at the mid-point. Calculate the supply voltage $V_A$ and phase angle between $V_A$ and $V_B$. [20 marks]
• Q2. (a) What are the bundled conductors? Discuss the advantages of bundled conductors when used for overhead lines. (b) The three conductors of a 3 - phase line are arranged at the corners of a right angled isosceles triangle. If each equal side of this triangle is $2\text{m}$, find line to neutral capacitance per $\text{km}$. Take the diameter of each conductor as $1.24\text{cm}$. The conductor are transposed at regular intervals. [20 marks]
• Q3. (a) Discuss why: (i) Transmission lines in heavily polluted area are provided with greater number of insulator discs. (ii) Insulators are fitted with arching horns. (iii) Insulators are polished. (iv) Pin type insulators are not preferred over $33\text{ KV}$. (b) A string of five suspension insulators is to be fitted with a grading ring. If the pins to earth capacitance are equal to C, find the values of line to pin capacitances that would give a uniform voltage distribution along the string. [20 marks]
• Q4. (a) How the size of the conductor used as distributor and feeder are decided? (b) Describe briefly the different types of d.c distributors. (c) Explain briefly the 'Skin effect' in a transmission line. On what factors do it depends? [20 marks]

Section - B

• Q5. (a) What is corona? What are the advantages and disadvantages of corona? How can the corona loss be minimized in transmission lines? (b) A certain 3 - $\phi$ equilateral transmission line has a total corona loss of $53\text{kw}$ at $106\text{kv}$ and a loss of $98\text{kw}$ at $110.9\text{kv}$. What is disruptive critical voltage? What is the corona loss at $113\text{kv}$? [20 marks]
• Q6. (a) What material are used for insulating of cables? Discuss advantages and disadvantages of each. (b) Derive expression for insulation resistance and capacitance of a single core cable. [20 marks]
• Q7. (a) Discuss the different ways of classifying the sub-stations. (b) Draw the key diagram of a typical $11\text{kv}/400\text{v}$ indoor sub-station. [20 marks]
• Q8. (a) Derive the formula for the electric stress in a single core cable. Where the stress is maximum and where it is minimum? (b) A $33\text{kv}$ 3-phase underground feeder, $3.4\text{km}$ long uses three single core cable. Each cable has a conductor diameter of $2.5\text{cm}$ and the radial thickness of insulation is $0.6\text{cm}$. The relative permittivity of dielectric is $3.1$. Find: (i) Capacitance of the cable per phase (ii) Charging current per phase (iii) Total charging $\text{kVar}$ (iv) Dielectric loss per phase if the p.f of the unloaded cable is $0.03$. (v) Maximum stress in the cable. [20 marks]