Eureka! Institutional Repository

The following thesis presents the development of a supervisory Control and Data Acquisition (SCADA) system that controls and presents data about water distribution network and sewage collection and disposal network. It includes a complete automation system, use of telecommunications networks and user-friendly depiction applications. The work presented is based on real life projects about the sewer systems of Ioannina city and Sifnos island. The sewer systems are responsible for transferring human wastes from the Urban environment to on-site Biological Wastewater Treatment Plants (WWTPs). One thing we have to be sure about is the system’s reliability and correct operation because failure might result in environmental damage which is especially hard on places like islands. The system consists of a local Programmable Logic Controller (PLC) which is responsible for the automation process and the connection of the local station with the control center. It uses analog level measurement sensors and reserve digital float switches in order to drive inverters and pumps that help to relocate the waste into the next stage of the sewage treatment process. The pumping systems are always in standby mode and the PLC takes in case of failure of one of them. In operational state, when the level rises above a limit that we have defined, a pumping system is activated in order to restore the level to another fixed limit, which stops the operation. As has been mentioned, the analog level measurement consists of the float switches, a function which is activated automatically in case of failure of the analog sensor or in case we choose so. The pumps cycle one at a time for best optimization of the use of the materials and the backup is automatically activated in case of failure. All the control and alarm signals and generally all the signals we measure are transmitted and received with the help of the control center. Also, the operator is given the possibility via a web interface to make the above settings or to check the operation of the system. The control center receives and manages the signals of the local station while the SCADA system is constantly updating the databases for their further analysis and makes all the data accessible to the operators.