Corona Interview Questions and Answers:
1. What is corona ?
Ans. When the voltage between conductors of an overhead line exceeds the disruptive critical voltage value, a hissing noise accompanied by a violet glow appears. This phenomenon is called the corona.
2. What are the various factors which affect corona ?
Ans. Factors affecting corona are (i) number of ions, size and charge per ion, mean free path depending on atmospheric conditions, (ii) line voltage, (iii) ratio of conductor spacing to conductor radius, (iv) contour of the conductor surface, and (v) state of the conductor surface.
3. What are the adverse effects of corona ?
Ans. Adverse effects of corona are
- power loss but not very important except under abnormal weather conditions,
- corrosion due to production of ozone gas, and
- interference with neighboring communication circuits.
4. What do you mean by dielectric strength of air ?
Ans. The value of potential gradient at which complete disruption of air occurs, is called the dielectric strength of air.
5. What is meant by disruptive critical voltage ?
Ans. The disruptive critical voltage is defined as the minimum phase to neutral voltage at which corona occurs.
6. What is visual critical voltage ?
Ans. Visual critical voltage is defined as the minimum phase to neutral voltage at which glow appears all along the line.
7. What are the various factors which affect corona loss ?
Ans. The factors affecting corona loss are system frequency, system voltage, air conductivity, air density, conductor diameter, conductor surface condition, atmospheric conditions and load current.
8. How can the corona effects be minimised ?
Ans. Corona effects can be minimised in a transmission line by using large diameter conductors which may be accomplished by using hollow conductors with a hemp core, ACSR conductors or bundled conductors. Corona effects can also be reduced but to a limited extent, by increasing the spacing between the conductors.