Operating Costs of Group Drive and Individual Drive

Author: E.E. Kimberly

The higher efficiency of the group-drive motor is offset at least in part by the losses in belting and shaft bearings. There may, however, be a saving in power costs with a group drive when the maximum demand for billing purposes is based on "connected horsepower" (see Chapter 24). Thus, it might be necessary because of peak loads to provide a 10-hp motor to drive a given machine. Ten such machines would require ten motors for individual drive, and the demand would be based on 100 connected horsepower. It might be possible to arrange these machines for group drive and use only a 40-hp motor, if the peak loads did not seriously overlap in the times of their occurrences, Thus, the demand charge for group drive would be only 0.4 times that for individual drive. Such economies in first cost and demand charges (see Chapter 24) can sometimes be effected. In the case of overtime work the group-drive motor must run badly under-loaded; at times it may be necessary to drive the whole line-shaft system to operate possibly only 10 per cent of the machines of the group.