Abstract :
P. S. Stevens: Mr. McNeill has mentioned the effect of electric power on the mechanical design of the shovel, such as better gearing, lubrication, etc. I would like to further point out that the variable-voltage control with separately excited motors described by Mr. McNeill is so complete and well suited to shovel operation that it has been possible to simplify the mechanical design of electric shovels without any sacrifice. For example, on two models of medium-sized shovels recently developed, the usual band-type air-operated clutch previously required for disconnecting the engine or motor from the hoisting drum has been omitted. This clutch has been omitted for the same reason also on a large 12-yard Diesel-electric dipper dredge recently put in operation. The elimination of this clutch and its operating mechanism, reduces the care and maintenance of the shovel and is made possible by the quick acceleration and quick and smooth stopping afforded by the separately excited motor control with motor lowering. The motor is actually driven down to a certain extent, so that fast lowering speed is obtained and the shovel operator can graduate his lowering speed or check it any time under perfect control.
