Published Resources Details
Journal Article
- Title
- Some aspects of lightning flashover and power outage performance of wood-insulated transmission lines (and Discussion)
- In
- Electrical and Mechanical Engineering Transactions
- Imprint
- vol. 4, Nov 1962, pp. 49-
- Description
[This paper was awarded the Institution Award 1962.]
- Abstract
This paper deals with the parameters of wood insulated transmission lines, which influence the transition from a lightning flashover into a permanent power arc.
Field experience has shown that the performance of wood-insulated transmission lines may be improved by utilising the arc quenching of the wood as well as its impulse insulation strength. It was suggested for softwoods that little further gain is obtained if the power frequency voltage gradient is reduced below 0.5 kV r.m.s./inch of wood and this result was confirmed by laboratory experiments using combined impulse and power frequency tests. It is believed that the full utilization of this property could reduce the ratio of lightning flashover to power fault outage to less than the average figures of 0.35 to 0.55.
A study of the arc properties of hardwoods carried out in the University of Queensland has shown that a relatively high voltage is required to maintain an arc confined in the pores of timber. It has been shown for lengths of wood from 3 to 120 inches (including wood-porcelain combinations on 11-kV and 33-kV structures) that the minimum arc voltage gradient required is generally greater than 1 kV/inch of wood.
It is suggested that this characteristic of wood, i.e., the high arc voltage, is responsible for the observed arc quenching properties. This gives rise to a simple design criterion, namely that the length of wood insulation should be chosen to ensure that the maximum power frequency voltage appearing across it after impulse flashover is less than the minimum voltage required to maintain the arc. Assuming that the probability of a transition from a lightning flashover to a permanent arc is determined largely by the relative magnitudes of the minimum arc voltage and the instantaneous system voltage, an analysis of the results suggests a safe minimum operating gradient for Australian hardwood of 0.7 to 0.8 kV r.m.s./inch of wood.
Considerably more work on the physics of the arc processes is necessary to enable the development of a more accurate criterion on a statistical basis.