JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year HIGH VOLTAGE ENGINEERING Previous Question Paper (September - 2021 - R18)
Answer any five questions
All questions carry equal marks
Main
List out the types of discharge and explain in brief.
Answer
Electrical discharges in gases are categorized based on the mechanism of electron production and the presence of an external ionizing source:
- Non-self-sustained discharge: This occurs when the discharge current depends on an external ionizing source, such as UV radiation or X-rays. If the external source is removed, the current ceases immediately.
- Self-sustained discharge: This occurs when the discharge current is maintained by the internal processes of the gas itself, primarily through secondary ionization (Townsend mechanism). Once initiated, it continues even if the external source is removed.
- Townsend discharge: A low-current, self-sustained discharge characterized by a uniform field where electrons gain sufficient energy to cause further ionization upon collision with gas molecules.
- Arc discharge: A high-current, low-voltage discharge characterized by high gas temperature and thermal ionization. It occurs at high current densities and is accompanied by intense light and heat.
- Corona discharge: A localized discharge occurring in non-uniform fields where the electric field strength near a conductor exceeds the breakdown strength of the surrounding gas, but is insufficient to cause a complete sparkover.
- Glow discharge: A steady-state discharge characterized by a luminous region near the cathode and a positive column, typically occurring at low pressures.
Distinguish between Ionization processes and de-ionization processes.
Answer
| Feature | Ionization Process | De-ionization Process |
|---|---|---|
| Definition | The process of creating charge carriers (ions and electrons) from neutral atoms or molecules. | The process of removing or neutralizing charge carriers to restore the gas to a neutral state. |
| Energy Requirement | Requires energy input (e.g., collision, radiation, thermal). | Releases energy (e.g., recombination energy). |
| Effect on Conductivity | Increases the electrical conductivity of the gas. | Decreases the electrical conductivity of the gas. |
| Key Mechanisms | Townsend primary/secondary ionization, photo-ionization, thermal ionization. | Recombination, diffusion, attachment. |
| Role in Breakdown | Essential for the initiation and growth of an electrical spark. | Opposes the breakdown process by reducing charge carrier density. |
Distinguish between Solid dielectrics and composite dielectrics and list out various insulating materials.
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Discuss about electromechanical breakdown and thermal breakdown in solid dielectrics.
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What are the different methods of generating high DC voltages and discuss in brief.
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Explain how to generate high impulse currents with necessary diagrams and what is the need of generating impulse currents?
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With neat sketch construct the cathode ray oscillographs for impulse current measurement.
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What are the methods to measure dielectric constant and loss factor and discuss.
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Discuss about lightning surges and switching over voltages.
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What are the various tests conducted on transformers? Explain each procedure.
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