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Insulator Flashover || conductivity || adherence || size ||
Dry volcanic ash is not conductive enough to cause insulator flashover problems. However, if insulating surfaces are completely coated in ash, the presence of moisture in association with soluble ash coatings can be critical factors in initiating insulator flashovers. Moisture may be derived from the atmosphere, in the form of rain during or after the ash fall, or from the eruption plume itself. The soluble coatings are derived from aerosols in the eruptive column. With time rain will dilute the soluble components. Finer ash has a higher conductive potential.
Weather conditions at the time of ash fall influence how ash adheres to insulating surfaces. Dry ash generally tends to rest on horizontal or gently sloping surfaces but causes no immediate electrical problems. In contrast wet ash sticks to all exposed surfaces. Experiments have shown that heavy rain can wash off about 66 percent of ash from insulators, whereas light rain removes little ash. In addition, tests have shown that winds of up to 55 km/hr can remove 95 percent of dry ash.
The type, condition and orientation of insulators have been found to influence the adherence of ash. Epoxy insulators are more vulnerable to flashovers than porcelain insulators due to increased ash adherence. Experiments have also showed that if insulators were wet prior to ash falls, adherence was enhanced. Especially significant was the ability for ash to accumulate on the underside of wet insulators. Insulation that has 30 percent or more of its creepage distance either clean or dry has a low probability of initiating insulator flashovers.
Since lower voltage insulators have smaller weather-sheds they are more prone to becoming completely covered with ash and water, and therefore are more vulnerable to flashovers than higher voltage insulators. Substation insulators are more susceptible to flashovers than line insulators because of their distinct shape and orientation.
Other Problems || increased corona activity || mechanical damage || wet ash || trees ||
Ash contamination on insulators and conductors increases corona activity which in turn causes increase in audible noise (around 10-15 dB) and radio interference.
Volcanic ash is a contaminant which abrades and clogs mechanically moving parts. Precautionary measures may be needed to service and maintain substation equipment after ash falls.
Saturated volcanic ash on ground surfaces has the potential to be hazardous due to its conductivity.
Wet ash-laden tree limbs may fall on distribution lines.
Historical eruptions: examples of effects of ash on power facilities and transmission
The consequences of loss of electricity supply are widespread, and many other public utilities (e.g. water supply pumps, radio and telecommunication facilities) may be inoperative for the duration of the power loss unless local backup power supplies (batteries and generators) are available.
|Volcano (Nation); Eruption year||Effects|
|Mount St. Helens (USA); 1980||Insulator flashovers in areas receiving >5 mm of ash, in conjunction with rain.|
|Redoubt Volcano (USA); 1989-90||Insulator flashovers in areas receiving ash, in conjunction with rain.|
|Rabaul (Papua New Guinea); 1994||Wire and cross arms damaged by collapsed buildings and tree breakage.|
|Ruapehu (New Zealand); 1995||Insulator flashovers on high voltage lines receiving moist ash.|
|Ruapehu (New Zealand); 1996||Flashover at substation due to water (from clean-up operations) settling on ash-covered insulators.|
|Copahue (Argentina); 2000||Heavy ashfall cut off power for several hours and eruption-related damage also cut off the power supply.|
Rabaul, Papua New Guinea: 1994
The 1994 eruption of Rabaul devastated much of the town of Rabaul, with ash deposits as thick as 2 m. The power supply was shut down at the start of the eruption but large sections of the reticulation system was damaged by falling-trees and buildings.
Ruapehu, New Zealand: 1995-1996
Falls of volcanic ash on 25 September 1995 caused shorting on high-voltage electrical power lines at the base of the volcano. This caused voltage fluctuations and problems for electrical equipment throughout the North Island. Cleaning of 18 transmission towers and insulators was undertaken on 27 September 1995 by four crews of four men.
The ash was found to be dry and easy to remove. Strain towers were the most affected due to their insulator configurations (horizontally strung). Rainfall on 26 September had washed away ash on the north side of the towers and insulators. It was concluded that normal rainfall would clean ash from structures, conductors, and insulators except the undersides of strain strings. Three strings of insulators were found to have widespread flashover damage but with no electrical problems. After ash falls electricity generation and supply companies routinely cleaned ash from affected substations.
On 17 June 1996 electricity supplies were disrupted in parts of Rotorua city after an explosion at a local substation caused by ash and water settling on a transformer due to a resident's hosing ash from the roof of a neighboring building.
Ash that falls dry on dry surfaces is easily cleaned by air blasting or brushing. Ash that falls wet or is wetted before cleaning is not easily removed without high pressure water or hand cleaning. To prevent widespread power outages ash should be removed from electrical supply facilities as soon as possible and from the most sensitive areas first.
The washing of insulators should start from the bottom up to minimize the chance of wet reworked ash forming a sufficient cover to induce flashover. If possible de-ionized water should be used. Suggested methods for the protection of electricity supplies include:
- Immediately after an ash fall, dust, sweep, and blow ash from electrical equipment at substations.
- Shut down all electrical systems (by throwing the main circuit breakers) before any attempt is made to clean or service them.
- Remove dry ash immediately from the most sensitive systems by blowing it off using air pressure of 30 psi or less, to avoid a sandblasting effect. Be careful not to blow the ash to other places that should be kept clean. Vacuum ash when possible and change filter bags often.
- Clean electrical components such as small motors and light bulbs, as they will generate excess heat when blanketed with dust. The excess heat can cause fires and short term operating life.
- Avoid saturating electrical components when hosing dust off. Many of these systems can handle rain and moisture, but not the effect of water jets from hoses.
- Check for trees heavily loaded with ash near power lines.
- Check and keep insulators clean. Ash that has hardened may require special cleaning methods such as hand cleaning or water jetting.
- Protect backup and auxiliary units to avoid starting problems when they are activated.
- Maintain protection and cleaning programs continuously until the threat of windblown ash is over.
Blong, R.J., 1984, Volcanic hazards: A sourcebook on the effects of eruptions: Academic Press, Australia, 424 p.
Blong, R., and McKee, C., 1995, The Rabaul eruption 1994: destruction of a town: Natural Hazards Research Centre, Macquarie University, Australia, 52 p.
Heiken, G., Murphy, M., Hackett, W., and W. Scott, 1995, Volcanic hazards on energy infrastructure of the United States: United States Department of Energy, LA-UR 95-1087.
Nellis, C.A., and Hendrix, K.W., 1980, Progress report on the investigation of volcanic ash fallout from Mount St Helens: Bonneville Power Administration, Laboratory Report ERJ-80-47.
Sarkinen, C.F., and Wiitala, J.T., 1981, Investigation of volcanic ash in transmission facilities in the Pacific Northwest: IEEE Transactions on Power Apparatus and Systems, v. PAS-100, p. 2278-2286.
Stember G.E., and Batiste, A.R., 1981, Impacts of Mt St Helens volcanic ash fallouts on the BPA System: Proceedings of the American Power Conference 1981, v. 43, p. 495-498.
Tuck, B.H., Huskey L., and Talbot L. 1992, The economic consequences of the 1989-90 Mt. Redout eruptions: Institute of Social and Economic Research, University of Alaska Anchorage, 42 p.