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 suitable data wherever missing.

Questions

Section-A

• Q1. (a) Derive a formula for the electric stress in a single core cable. Where is the stress maximum? Where is it minimum? (10) (b) A single core cable for $66\text{ kV}$ 3-phase 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 inter sheaths. Also find the maximum and the minimum stress if the inter sheaths are not used. (10) [20 marks]
• Q2. (a) What materials are used for the insulation of cables? Discuss the advantages of each. (10) (b) A single core cable $1.0\text{ km}$ long has a core diameter of $0.5\text{ cm}$ and diameter under sheath $2.0\text{ cm}$. The relative permittivity of the insulating material is $3.5$. The power factor on open circuit is $0.05$ and the supply voltage is $11\text{ kV}$, $50\text{Hz}$. Determine: i) The capacitance of the cable ii) The charging current per conductor iii) The dielectric loss and iv) The equivalent insulation resistance. (10) [20 marks]
• Q3. (a) Derive the expression for power in terms of symmetrical components for unbalanced three phase circuit to show that $V_a I_a^* + V_b I_b^* + V_c I_c^* = 3 V_0 I_0^* + 3 V_1 I_1^* + 3 V_2 I_2^*$ (10) (b) What do you understand by sequence networks? What is its importance in unsymmetrical fault calculations? (10) [20 marks]
• Q4. (a) Derive necessary equations to find fault current and interconnection of sequence networks for LLG fault. (10) (b) Discuss phase shift of symmetrical components in $Y-\Delta$ transformer banks. (10) [20 marks]

Section-B

• Q5. (a) What is per unit system? How are the base quantities selected? (8) (b) Describe briefly about the one line diagram. (6) (c) What are the advantages of p.u. System? (6) [20 marks]
• Q6. The one-line diagram of an unloaded power system is shown in fig. 1. Reactances 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 $\text{T}_1$: $25\text{ MVA}$, $220\text{Y}/13.8\Delta\text{ KV}$, $X = 10\%$ 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 reactances marked in p.u. Choose a base of $50\text{MVA}$, $13.2\text{ KV}$ in the circuit of generator. (20) [20 marks]
• Q7. (a) What are BILS? Explain their significance in power system. (10) (b) What are various causes of over voltages surges in various parts of power system? Name different factors which affect the switching over voltage due to circuit breaker. (10) [20 marks]
• Q8. (a) What are the factors to be considered at the time of coordinating insulation in the substation? (10) (b) Deduce the method of selection of arrester rating in view of insulation coordination. (10) [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