Substations & Switchyards

Immediate cleaning of substation equipment has been used as either a reactive or proactive measure against ash-induced flashover (e.g. Mt. St. Helens 1980, Redoubt 1989, Ruapehu 1995-96, Tungurahua 2010, Shinmoe-dake 2011). Ash thicknesses received at substations during eruptions have been wide-ranging; however, cleaning has commenced with ash deposits as thin as 1 mm (Guayaquil, Ecuador following the 2010 eruption of Tungurahua). In every documented instance where cleaning of substations has taken place, insulator flashover has been avoided and power companies have been successful in maintaining power supply.

The lack of sensitive apparatus such as power transformers means that ash contamination at switchyards will have a lower probability of disrupting power supply. This suggests that switchyards are less vulnerable to ash-induced impacts than substations.

Reduction in substation/switching station gravel resistivity was reported following the 1980 Mt. St. Helens eruption. However, field research suggests replacement of contaminated substation gravel is not required so long as the ash and gravel mixture displays a resistivity value >3,000 Ωm, as prescribed by IEEE Standard 80 (2000).