Development of data acquisition and load control system by programmable logic controller for high voltage load customer

This paper proposes a PC based data acquisition and load control system (DAALCS) to fulfil load management functions for a high voltage load customer. A programmable logic controller (PLC) associated with a digital power meter has been applied to fulfil major application functions of DAALCS. In the data acquisition subsystem, two PLCs with redundant configuration are responsible for directly collecting power measurements via star connection telephone network with real time mode. 15 digital power meters with standard RS485 protocol are installed on each building substation to record more than 20 parameters for data acquisition subsystem. In the load control subsystem, six sets of PLCs with the mixture of PLC network and RS 485 channel are constructed to execute load control schemes. The load control schemes are composed of load shedding for demand monitoring, cycling on/off load control, timer control, and direct load control. The proposed system has been successfully installed and continuously operated on an academic power system. The statistical data retrieved from the database shows that the DAALCS can effectively reduce the daytime peak load during the summer season and significantly save electric energy consumption