A. a line breakdown
B. a flash-over
C. a puncture
D. less sag
Answer: B. a flash-over
Explanation:
Concept of Flashover Voltage:
- The overhead line conductors should be supported on the poles or towers in such a way that currents from conductors do not flow to earth through supports i.e., line conductors must be properly insulated from supports. This is achieved by securing line conductors to supports with the help of insulators. In general, the insulators should have the following desirable properties.
- High mechanical strength in order to withstand conductor load, wind load, etc.
- The high electrical resistance of insulator material in order to avoid leakage currents to earth.
- The high relative permittivity of insulator material in order that dielectric strength is high.
- The insulator material should be non-porous, free from impurities and cracks otherwise the permittivity will be lowered.
- High ratio of puncture strength to flashover
- An insulator is so designed that it should fail only by a flash-over. A flashover arc is a breakdown and conduction of the air around or along the surface of the insulator, causing an arc along the outside of the insulator. Insulators are usually designed to withstand flashover without damage.