Transmission and Distribution Grounding in The Hydro-Electric Power Commission of Ontario

Accepted grounding methods have been modified for use in areas having difficult grounding conditions. Satisfactory transmission line grounding in rocky areas is obtained economically where the improved methods are followed. Long rods are effective in reducing distribution neutral voltages to an acceptable sustained maximum of 15 volts, which introduces a negligible hazard. Measurements taken on an air-switch installation showed the superiority, over that with rods alone, of a grounding arrangement incorporating a mat or grid. On the basis of these tests, it is proposed to use such a mat to control the potentials possible between switch handle and ground. Personnel and equipment at generating stations under construction are protected from fault currents by connecting all equipment on the ungrounded distribution system to a common metallic circuit. Ground detectors are used if this arrangement is not practical. Completed stations are safely grounded both for power-frequency system faults and lightning surges. In most instances, separate grounding arrangements are necessary for each type of installation.