Power quality and factory automation

Limited information exists on the power quality profile and requirements of large automated manufacturing plants. A case study is described to monitor power quality disturbances at a representative plant and identify the disturbances that disrupt production. The sensitivities of representative electronic control equipment to the identified disturbances were measured and then projected to form a plant disturbance threshold. For the monitoring effort, six disturbance analyzers were installed at four voltage levels extending from the utility 40 kV station to 120 V control power in an individual machine tool. Voltage sags were the only disturbance at 68% of the total number of events recorded. Two PLC (programmable logic controller) transfer lines and a CNC (computerized numerically controlled) lathe were tested with a sag generator to determine the sensitivities of the equipment. The calculated sag threshold at the utility feed to the plant to disrupt production was 87% of nominal voltage for more than 8.3 ms.<>