Serious corrosion of mine traction systems using positive-polarity grounding of direct current supply equipment is described. Abnormally increased costs from excessive trolley insulator failures and a safety hazard resulting from possible formation of pure metallic sodium or potassium in corrosion products are reported.
As a consequence of these conditions, Tennessee Coal and Iron Division of U. S. Steel Corporation has converted the only two of its mines in which the traction systems were designed for positive-polarity grounding of negative-polarity trolleys.
Reasons for the installation in mines of positive-polarity systems are given. Illustrations show how the corrosive electrolysis destroys the rock in which trolley supports are fastened.
Tests indicate the presence of pure sodium or potassium in corrosion products. These metals will cause skinburns and when bits of the crusty deposit formed on the insulator fell into pools of water on the mine floor an explosive reaction accompanied by flame occurred.
The extent of possible economic effects of these corrosive reactions on the mine transport systems are given.
