Solution for High Voltage Engineering

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Bennett Cobb
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1 Solution for High Voltage Engineering December 2015 Index Q.1) a).2 b).3 c).4-6 d).7 e). 8-9 Q.2) a) b) Q.3) a) b) Q.4) a) b). N.A Q.5) a).30 b) Q.6) a) b)

2 Q1Attmpt any four (a) What are electronegative gases? Why is the breakdown strength higher in these gases compared to that in other gases. (05) Ans: Break Down in Electro negative Gases :- 2

3 (b) Explain the phenomenon of tracking in solid insulating materials under the electrical stress. How it can be minimized. Ans: Breakdown Due to Treein g and Tracking 3

4 (c) With a neat sketch explain trigatron spark gap used in impulse generators. (05) Ans :- Tripping and Control Impulse Generators 4

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7 (d) What are commercial liquid dielectrics, and how are they different from pure liquid dielectric? (05) Ans: Pure Liquids 7

8 (e) With a neat sketch explain Hall Generators for measurements of high current. (05) Ans: Measurement of High Value DC Current by Fall- Generator 8

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10 Q2 (a) Explain with neat diagrams the principal of operation of an Electrostatic voltmeters.discuss its advantages and limitation on high voltage measurements. (10) Ans: Electrostatic Voltmeter 10

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12 (b) Why is Cockcroft-Walton circuit preferred for voltage multiplier circuits? Explain its working with a schematic diagram. (10) Ans: Cockroft Walton Voltage Multiplier Circuit 12

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15 (5) Similarly C1 must acquire for stability reasons a charge 3q so that it can supply a charge q to the load and 2 q to capacitance C2 in next half cycle (6) During the transformer cycle shown in figure (b).the diodes D1,D2, D3 conduct when B is positive with respect to A. 15

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19 Q3)(a)What is Paschen s law? How to do account for the optimum voltage for breakdown under a gi ven p X d condition? (10) Ans :- Paschens Law It state that, Breakdown voltage of uniform filed gap is unique function of product of p, i.e gas pressure and d i.e. electrode gap distance for a particular gas and for a given electrode material According to Townsends breakdown Criteria γ and α both are function of E/P 19

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23 (b)describe in brief various tests carried out on overhead line insulators. Testing Insulator :- 23

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27 Q4(a) Explain how a sphere gap can be used to measure the peak value of voltages.what are the parameters and factors that imfluence such voltage measurement? Ans: Sphere Gap Meter 27

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30 (b) In an experiment in a certain gas it was found that the steady state current is 5.5 x 10-8 A at 8KV at distance of 0.4 cm between the plane electrodes.keeping the field constant and reducing the distance to 0.1 cm results in a current of 5.5 x A.Calculate Townsend s primary ionization coefficient alpha. (10) Ans: N.A. 30

31 Q5(a) Explain the various theories that explain breakdown in commercial liquid dielectric. (10) Ans: Conduction and Breakdown Commercial Liquids 31

32 (b) What is thermal breakdown in solid dielectric,and how is it practically more significant than other mechanism. (10) Ans: Thermal Breakdown 32

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34 Q6(a) Describe the construction principle of operation and application of 3- state Marx generator circuit. (10) Ans: Multistage Impulse Generators Marx Circuit 34

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37 (b)what are the various factors to be considered while designing a high voltage laboratory. (10) Ans: Classification of HV Laboratories 1)A small size Labpratory 2)Medium Size Laboratory 37

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OR Explain thermal breakdown in solid dielectrics. How this mechanism is

OR Explain thermal breakdown in solid dielectrics. How this mechanism is Subject : High Voltage Engineering (2090) ITM Universe, Vadodara Electrical Engineering Department Class : Electrical Sem : th Long Questions Sr. No Question Unit No : 0 Explain Charge Simulation method