By Michael A. Stout
Clean, reliable water resources are the foundation of growth in the United States’ arid southwest.
Beginning with a controversial aqueduct designed by William Mulholland in the early 1900s, the Department of Water and Power (DWP) has provided Los Angeles with a major water supply.
At the same time, diversion of the Colorado River brings water to parched desert cities of Arizona, New Mexico and California.
Both sources transform dry desert land into something more like a vast oasis.
Yet with the ongoing drought in the Southwest, these vital resources are increasingly limited, with cost increasing accordingly. Local water treatment facilities are the key to efficiently manage, recycle and distribute this precious resource.
Water utilities therefore seek solutions that reduce costs by eliminating process-treatment downtime.
No more by hand
The automation systems used in these remote, arid regions have some notable characteristics.
The distributed treatment process typically is monitored by supervisory control and data acquisition (SCADA) systems. Remote terminal units (RTU) manage the pumps, valves, meters and cameras, as well as sampling and other processes that are distributed throughout the treatment facility.
The RTU, which in most respects is similar to the better-known programmable logic controller (PLC), is a microprocessor-enabled electronic device that, dependent on make and model, can have input/output (I/O) that number in the thousands and that is an interoperable node in SCADA.
RTUs are located in enclosures throughout the facility, connected to the main SCADA control center, located as far as a mile away from the main treatment facility. The control center houses the main SCADA server, operations, maintenance, IT, engineering and other staff necessary for water treatment operation.
Automated systems, SCADA itself and even plant security systems are totally dependent on reliable sources for AC power.
Microprocessor-based SCADA and security systems are often power sensitive and rely on a high-quality power source protected from outages. With large motors and pumps connected to the facility’s power system, plant utility power can become polluted with voltage sags, over-voltage conditions, and destructive high-voltage transients.
Utility power can also experience short and long-term outages.
Listen, and don’t…
Much in use, uninterruptible power supplies (UPS) condition power to SCADA systems and are a backup power source, supporting minutes or even hours of backup. Many of these system elements are installed outdoors and exposed to the elements.
Unscheduled downtime due to the improper use of office-grade UPSs in these harsh environments is common in the industry. The electronics in office-grade UPSs are not meant to operate reliably in the high temperature and the corrosive gas environments present in Southwestern water treatment plants.
That’s because plant-wide SCADA typically consists of a large number of NEMA outdoor enclosures containing the UPS and networking peripherals responsible for controlling thousands of distributed control/measurement nodes.
A major slowdown of operations can follow a UPS failure or battery problem, shutting down the affected