Abstract :
In the past, coal mines have received their electric power from large centralized stations consisting of rotating equipment or mercury-arc rectifiers which furnished low-voltage dc power which was distributed on large copper conductors to the working area of the mine. The "solid-state era" entered the coal industry in the late 1950s and made compact, decentralized, simple power rectification possible. The new developments in rectifier design were so successful that soon larger, more complex, highly protected units were replacing the older, less efficient methods of conversion. At the beginning of the solid-state era conventional dc circuit breakers were too large to meet low-height mining requirements. Molded case breakers were found to have sufficient speed, capacity, and reliability to fulfill electrical design requirements; therefore, molded case breakers made the first low-height solidstate rectifier designs possible. Low-profile mining equipment must be compact and designed to operate in damp, moist atmospheres prevalent in coal mines. Tests must be made to determine that the cooling air is not impeded and that all materials insure adequate insulation levels. Components must be mounted to offer the best possible cooling and still prevent electrical creepage problems.
