R05320206-high-voltage-engineering

Set No. 1

Code No: R05320206

III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 HIGH VOLTAGE ENGINEERING (Electrical & Electronic Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Discuss the applications of solid insulating materials in high voltage power transformers. [16] 2. Show graphically the relation between the breakdown field strength of a gas and the gas pressure for uniform field with a constant electrode separation. Give the physical explanation of the curve. [16] 3. Explain properties and applications of Glass and Ceramic insulating material used in high voltage engineering. Compare their merits and demerits. [16] 4. (a) Explain and compare the performance of half wave rectifier and voltage double circuits for generation of high DC voltages. (b) A 10 stage Cockroft - Walton circuit has all capacitors of 0.1 µF. The secondary voltage of supply transformer is 11 kV at a frequency of 50 Hz. If the load current is 2 mA, find i. the voltage regulation ii. ripple voltage.

[8+8]

5. Discuss various capacitance, potential dividers and compare their performance for measurement of impulse voltages? [16] 6. (a) Explain the different theories of charge formation in clouds? (b) What are the mechanisms by which lightning strokes develop and induce over voltages on overhead power lines? [8+8] 7. Explain the concept of apparent charge in partial discharge measurements. Describe a simple experiment technique to measure partial discharge [16] 8. Mention the different electrical tests done on isolators and circuits breakers. [16] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: R05320206

III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 HIGH VOLTAGE ENGINEERING (Electrical & Electronic Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Discuss the applications of insulating materials in construction of bushings. [16] 2. (a) Mention the names of the gases which are used in the Electrical apparatus as an insulating medium. (b) Discuss about the electrical properties of gases. (c) Discuss about various physical conditions of gases to govern the ionization process. [5+5+6] 3. What is internal discharge? How it is different from treeing and tracking. Explain these mechanisms briefly and discuss their affects on solid insulation breakdown in practice. [16] 4. (a) Explain a Cockroft-Walton circuit with a schematic diagram? (b) Why is a Cockroft-Walton circuit preferred for voltage multiplier circuits? [8+8] 5. (a) Discuss various methods of measuring high d.c and a.c currents. (b) Mention various methods of measuring high impulse currents. 6. Give the mathematical models for lightning discharges and explain them.

[8+8] [16]

7. Explain the concept of apparent charge in partial discharge measurements. Describe a simple experiment technique to measure partial discharge [16] 8. Describe the impulse current tests performed on lighting arrestors. How do you conclude that the arrester has passed the test? [16] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: R05320206

III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 HIGH VOLTAGE ENGINEERING (Electrical & Electronic Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Explain the applications of insulating materials in the construction of circuit breakers. [16] 2. Explain various primary ionization processes of Townsend’s mechanism. Derive an expression for current growth due to these processes. [16] 3. Derive the expression for critical electric field and show that the field is independent of critical temperature of the dielectric. State the assumptions made. [16] 4. (a) Explain and compare the performance of half wave rectifier and voltage double circuits for generation of high DC voltages. (b) A 10 stage Cockroft - Walton circuit has all capacitors of 0.1 µF. The secondary voltage of supply transformer is 11 kV at a frequency of 50 Hz. If the load current is 2 mA, find i. the voltage regulation ii. ripple voltage.

[8+8]

5. Discuss the problems associated with peak voltmeter circuits using passive elements. Draw the circuit developed by Rabus and explain how this circuit overcomes these problems? [16] 6. Discuss the power frequency over voltages in power systems. Explain various protection schemes employed to suppress the over voltages? [16] 7. Explain the high voltage Schering bridge for the tan δ and capacitance measurement of insulators (or) bushings? [16] 8. Mention the different electrical tests done on isolators and circuits breakers. [16] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: R05320206

III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 HIGH VOLTAGE ENGINEERING (Electrical & Electronic Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. What are the different dielectric materials according to their physical nature? Compare their merits and demerits. [16] 2. The following observations were made in an experiment for determination of dielectric strength of transformer oil. Determine the power law equation. [16] Gap Spacing (mm) 4 6 8 10 Breakdown voltage (kV) 88 135 165 212 3. Discuss about various forms of plastic insulating materials used in high voltage engineering. Compare their relative merits and demerits with respect to their applications. [16] 4. (a) How are the wave front and wave tail times controlled in impulse generator circuits. (b) An impulse generator has eight stages with each condenser rated for 0.16 µF and 125 kV. The load capacitor available is 100 pF. Find the series Resistance and damping Resistance needed to produce 1.2/50 µs impulse wave. What is the maximum output voltage of the generator, if the charging voltage is 120 kV? [8+8] 5. (a) Describe the generating voltmeter used for measuring high d.c voltages. How does it compare with a potential divider for measuring high dc currents. (b) A generating voltmeter is to read 250kV with an indicating meter having a range of (0-20) µA Calibrated accordingly . Calculate the capacitance of the generating voltmenter when the driving motor rotates at a constant speed of 1500 Rpm [8+8] 6. Give the mathematical models for lightning discharges and explain them.

[16]

7. (a) What are partial discharges? Differentiate between internal and external discharges? (b) Develop and draw equivalent circuit of insulating material during partial discharge? [16] 8. Mention the different electrical tests done on isolators and circuits breakers. [16] ⋆⋆⋆⋆⋆

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