SCADA Systems

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The advancement of modern communication technology has enabled the provision of real-time or near real time data, with the potential to improve asset management of infrastructure systems. Promising results have been achieved in issuing alerts for abnormal events that help engineers to initiate necessary action plans in a timely manner. In addition, the online data analysis enriches the understanding of system characteristics and facilities the application of data-driven methodologies for predicting short-term future conditions.

Online monitoring technology has long been employed by the water industry. A SCADA system relies on process monitoring sensors to convert physical phenomena (e.g., pressure or flow rate) into electronic signals that can be integrated by the control system. SCADA systems rely on the combination of sensor inputs to determine the state of the system, which is then used to modify the control inputs to the system. In a leakage context, a SCADA system requires the use of a computer, sensor data acquisition (e.g., telemetry), and an analysis algorithm to evaluate the sensor data and produce a leakage determination. The cost of sensors and data communication equipment necessary for implementing a full SCADA system on large water distribution systems has been seen in the past as prohibitive – especially for a water pipeline network where there is a lack of perceived environmental impact from a large-scale leak – however, this perception is changing. Linking hydraulic (and potentially water quality) models to telemetry systems is possible by calibrating and validating in real-time with data supplied by a SCADA system. Such a system could then potentially be integrated with dynamic leak detection and location methods, thus allowing the supervision and automatic assessment of the hydraulic performance of the system in terms of demand growth and leakage detection.

Field-based assets include:

• Wells,
• Pump stations,
• Valves,
• Treatment plants,
• Tanks and reservoirs.

For a water distribution network, the common objectives of a SCADA system are to do following:

• Monitor the system
• Obtain control over the system and ensure that required performance is always achieved
• Reduce operational staffing levels through automation or by operating a system from a single central location
• Store data on the behaviour of a system and therefore archive full compliance with mandatory reporting requirements for any regulatory agency
• Provide information the performance of the system by minimizing the need for routine visits to remote sites and potentially reduce power consumption during pumping operations through operational optimization
• Provide a control system that will enable operating objectives to be set and achieved
• Provide an alarm system that will allow faults to be diagnosed from a central point, thus allowing field repair trips to be made by suitably qualified staff to correct the given fault condition and to avoid incidents that may be damaging to the environment

Components of a SCADA System

SCADA encompasses the transfer of data between a SCADA central host computer and a number of remote sites (Remote Terminal Units) and the central host and the operator terminals. One or more field data interface devices usually called Remote Stations, Remote Terminal Units (RTUs) or Programmable Logic Controllers (PLCs), which interface to field sensing devices and local control switchboxes and valve actuators.

RTUs provide electronic field data interface. RTUs are primarily used to convert electronic signals received from (or required by) field devices into (or from) the language (known as the communication protocol) used to transmit the data over a communication channel.

PLCs connect directly to field data interface devices and incorporate programmed intelligence in the form of logical procedures that will be executed in the event of certain field conditions.