Water: SCADA Replacement
Project Overview

A major New York water utility company selected a PLC/SCADA-based control system to replace their existing RTU-based system.  The system controls and monitors their water production and distribution facilities, which serve approximately 60,000 customers with 28 million gallons of water per day.  The main reason for the project was the obsolescence of the RTU-based system, making spare parts and support services virtually impossible to obtain.

A PLC/SCADA platform was chosen due to the large installed based, vendor commitment to long-term product support, and an open architecture solution which enabled configurable interfaces to other platforms such as relational databases, other PLC systems, etc.
The Application

The utilities water distribution system consists of wells, treatment plants, pumping stations, storage tanks, pressure regulating valve installations, and numerous miles of water main lines. Approximately eighty (80) RTUs are dispersed throughout the distribution network to permit remote monitoring and control from the main control site.  Communications from the main site to the RTUs occurs via wireless radio frequency technology.

Initially, seventeen (17) of the eighty (80) RTUs were scheduled for replacement.  For those seventeen (17), the new PLC-based system provided all the functionality of the RTUs, but also enabled better diagnostic and reporting capability.  They monitored variables such as water flow, pressure, and level as well as controlled devices such as pumps and valves.  The remaining sixty-three (63) were then phased in for replacement.  Note that the main control site is able to communicate to all PLCs and RTUs in the distribution network independent of the PLC to RTU ratio in the system at any given time.  This was a requirement by the utility company.

The supervisory control system for the PLCs is a PC-based SCADA (Supervisory Control and Data Acquisition) system. Present day SCADA systems are designed to couple a user-friendly operator interface with all the control and monitoring capability of traditional systems.  In conjunction with “open” database software, they also provide advanced data collection, trending, reporting, alarming, and diagnostic functionality.
ACC System Architecture

The system architecture consists of a PLC system, a SCADA system, and a relational database. 

The PLC system is comprised of redundant GE PLCs, which are located at the main control site and communicate directly to the SCADA system.  They also communicate remotely via radio frequency modems to the (80) remote sites.

The system provides a very flexible and configurable tool to define the polling order of the remote PLCs; system parameters such as the number of retries, time between retries, etc. are accessible and modifiable using this tool.

The SCADA system consists of two (2) nodes of GE Proficy iFIX software.  They are configured to communicate via Ethernet to the redundant GE PLCs. An Oracle database is used as the data repository.  A variety of reports for operational and regulatory requirements are generated from the data in Oracle.
The Results

This project resulted in a flexible and reliable system which the customer finds easy to use, maintain, and modify.  Feedback from the operators is very positive.  The customer has taken complete ownership of the system and has standardized on many of the system components for other applications. 

The system data collection rate (measured by the time to poll all the remote sites) was greatly reduced through this project.  The legacy system required (4) to (8) minutes (depending on conditions) to poll all the RTUs.  The new system has the capability of polling all the PLCs in approximately 30 seconds; this poll time is artificially slowed down to (1) minute by introducing time delays in between radio contacts.  In addition, commands, such as start/stop pumps, etc. interrupt the polling cycle and are executed immediately.

The customer has since contracted with ACC to provide another, similar system for their operations in a nearby state.