Power System-II 2018 Question Paper — Government College of Engineeri…

Instructions

• Attempt five questions in all selecting at least two questions from each Section.
• Assume missing data wherever required.
• All questions carry equal marks.

Questions

Section - A

• Q1. (a) What materials are used for the insulation of cables? Discuss the advantages of each. (b) A $33\text{ KV}$, $3-\phi$, 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 $\text{K Var}$ (iv) dielectric loss per phase if the power factor of unloaded cable is $0.03$ (v) maximum stress in the cable. [20 marks]
• Q2. (a) Derive the formula for calculating current rating of a cable. What factors affect this rating? (b) A single core cable for $66\text{ KV}$, $3-\phi$ system has a conductor of $2\text{ cm}$ diameter and sheath of inside diameter $5.3\text{ cm}$. It is required to have two inter sheaths so that stress varies between the same maximum and minimum values in the three layers of dielectric. Find the positions of inter sheaths, maximum and minimum stress and voltages on the intersheaths. Also find the maximum and the minimum stress if the intersheaths are not used. [20 marks]
• Q3. (a) Derive necessary equations to find fault current and interconnection of sequence networks for line to ground fault at the terminals of the alternator. (b) Estimated short circuit $\text{MVA}$ at the bus bars of a generating station $1000\text{ MVA}$ and other station is $666\text{ MVA}$. The generated voltage of each station is $11\text{ KV}$. Determine the possible short circuit $\text{MVA}$ at each station when they are linked by an interconnected cable with a reactance of $0.5\text{ ohm}$. [20 marks]
• Q4. (a) Derive the expression for power in terms of symmetrical components for unbalanced three phase circuit to show that $V_a I_a^* + V_b I_b^* + V_c I_c^* = 3 V_0 I_0^* + 3 V_1 I_1^* + 3 V_2 I_2^*$ (b) One conductor of a three phase line is open. The current flowing to the $\Delta$ - connected load through line 'a' is $10\text{ A}$. With the current in the line 'a' as reference and assuming the line 'C' as open. Find the symmetrical components of the line currents. [20 marks]

Section - B

• Q5. (a) Classify the types of HVDC links. Discuss the applications of each of these links. (b) Briefly discuss the advantages and the operational problems of HVDC transmission. [20 marks]
• Q6. (a) What are various causes of over voltage surges in various parts of power system? Name different factors which affect the switching overvoltage due to circuit breaker. (b) What is the basic impulse level? Give its values for 33, 132, 220 and $400\text{ kv}$ effectively grounded system. [20 marks]
• Q7. (a) What is per unit system? Write different expressions that may be useful in per unit system for single phase and three phase systems. Derive the necessary expressions. (b) Show that the $p.u.$ equivalent impedance of a two winding transformer is same on both sides whether the calculation is made from the low voltage side or from the high voltage side. [20 marks]
• Q8. The one - line diagram of an unloaded power system is shown in Figure. Reactance of the two sections of transmission line are shown on the diagram. The generators and transformers are rated as follows: Generator 1 : $20\text{ MVA}, 13.8\text{ kV}, x'' = 0.20\text{ p.u.}$ Generator 2 : $30\text{ MVA}, 18\text{ kV}, x'' = 0.20\text{ p.u.}$ Generator 3 : $30\text{ MVA}, 20\text{ kV}, x'' = 0.20\text{ p.u.}$ Transformer $\text{T}_1$ : $25\text{ MVA}, 220\text{ Y}/13.8\text{ }\Delta\text{ kV}, x = 10\%$ Transformer $\text{T}_2$ : Single phase units each rated $10\text{ MVA}, 127/18\text{ KV}, x = 10\%$ Transformer $\text{T}_3$ : $35\text{ MVA}, 220\text{ Y}/22\text{ Y KV}, x = 10\%$ Draw the impedance diagram with all reactance marked in per unit. Choose a base of $50\text{ MVA}, 13.2\text{ KV}$ in the circuit of generator 1. [20 marks]

Related pages

• Power System-II syllabus
• All Power System-II papers from 2018

Other years

• Power System-II 2018 question paper — end-term
• Power System-II 2018 question paper — end-term