- Lightning over voltages.
- Switching over voltages.
- Although polymers are now the most common insulation materials at low voltages, at high voltages, most insulation is still based largely upon paper and oil. Such insulation systems are used in cables, transformers and bushings.
- Consequently, understanding their behavior when exposed to high fields and elevated temperatures for prolonged periods are of great practical importance.
- In transformers, for example, the oil serves the dual role of electrical insulation and a medium by which heat dissipated in the transformer windings and core is transferred to the environment.
- Work is currently being undertaken on examining the macroscopic properties of mineral oil subject, to both electrical and thermal ageing.
- Also, we are exploring the basic chemistry of ageing in oil systems, to enable us to develop simple analytical techniques that can be used in practice to provide an accurate representation of the integrity of high voltage plant.
- The work is extremely multidisciplinary in nature, involving a combination of electrical measurements and chemical characterization using optical spectroscopes, mass spectrometry, chromatography and related analytical techniques.
VARIOUS REGIONS OF THE CLOUD
- The upper regions of the cloud are positively charged, whereas the lower region and the base are predominantly negative except the local region near the base and the head which is possible.
- A thunder cloud consists of super cooled water droplets moving upwards and large hailstones moving downwards.
- The requirements for the thunder clouds and charge formation of air currents are moisture and specific temperature range
Different theories of charge formation
- Simpson’s theory
- Reynold’s theory
- Mason’s theory
- When a direct lightning stroke occurs on a tower, the tower has to carry huge impulse currents.
- If the tower footing resistance is considerable, the potential of the tower rises to a large value, steeply with respect to the line and consequently a flashover may take place along the insulator strings .This is known as back flashover.