52126-mt----high Voltage Engineering & Insulation Coordination

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Code No: 52126/MT M.Tech. – I Semester Supplementary Examinations, September, 2008

HIGH VOLTAGE ENGINEERING & INSULATION CO-ORDINATION (Common to Electrical Power Engineering/ Power Engineering & Energy Systems ) Time: 3hours

Max. Marks:60

Answer any FIVE questions All questions carry equal marks --Describe with a neat sketch, the working of a Van de Graff generator. What are the factors that limit the maximum voltage obtained?

1.

2.a)

Enumerate the different circuits used for producing impulse waves and obtain the impulse voltage wave equation of RC circuit with wave tail resistance on generator side. b) An 8 – stage impulse generator has 0.12 µF capacitors rated for 167 KV. What is its maximum discharge energy? If it has to produce a 1/50 ns wave form across a load capacitor of 15,000 PF. Find the values of the wave front and wave tail resistances?

3.a) b)

Explain the streamer theory of break down in gases. Briefly explain the different mechanisms by which breakdown occurs in liquid dielectrics.

4a)

Explain the principle, operation and construction of electro-static voltmeters for measuring high AC and DC voltages. What are the different types of resistive shunts used for impulse current measurements?

b) 5.

Explain the different electrical tests done on power transformers and Bushings?

6.a)

What are the causes for switching and power frequency over voltages? How are they controlled in power systems? Explain the different aspects of insulation design and insulation co-ordination adopted for EHV systems.

b) 7.a) b)

Compare Gas insulated substations and Air insulated substations? What is the criteria used in selecting the ratings of the testing equipment for H.V. Laboratories?

Contd…2 Code No: 52126/MT 8.

Write (a) (b) (c) (d)

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any two of the following: Paschen’s law and Townsend’s criterion for breakdown. Measurement of voltages by sphere Gaps Cascaded Transformers High voltage Schering bridge. &_&_&_&