Making Water Flow with Batteries

In many parts of the world, clean water from the tap is the most obvious thing ever. But maintaining a steady water supply is by no means an easy task. And just like any other critical infrastructure, it requires a lot of batteries.

The heart of a modern water purification plant is a SCADA, or Supervisory Control and Data Acquisition system. Integrated throughout the facility, this network both monitors and controls its operations. However, many of the sensors and other hardware contain sensitive microchips and generally rely on stable power supply. While the plant operates large pumps and motors that can cause significant voltage sags or over-voltage. 

Therefore, double-conversion online Uninterruptible Power Supply systems (UPSs) are used to clean” the utility power. Before it's fed to the plant's equipment, the electricity first has to pass through an AC-to-DC rectifier and then through an inverter to convert it back. This way, the UPS filters out any power disturbance, in addition to being able to provide several minutes to many hours of backup power.  

The systems deployed in water treatment plants are not just any office-grade UPSs, but the most rugged ones designed to withstand the high temperature and corrosive gas environment found in these facilities. And they need to be paired with equally robust batteries which have a wide operational temperature range. Which is why Ni-Cd batteries are the first choice for this particular application. 

An invisible network 

Until the water is pushed out into the distribution system, all processes are tightly controlled. However, monitoring the water distribution infrastructure is much more difficult and expensive. From the treatment plant, large diameter mains called primary feeders run in all directions. Along the way, they narrow into secondary feeders from which small diameter service lines branch off to the users.  

At the center of service locations, usually at the end of primary feeders, two general types of distribution reservoirs are located. While service reservoirs ensure the system has enough water to respond to fluctuating demands, balancing reservoirs are used to equalize the operating pressure. To prevent contamination, both underground and surface reservoirs are usually covered.  

In order to monitor such a dense network, operators use a range of instruments including pressure sensors, flow meters, rain gauges, or water quality analyzers. And to remotely control it, pump stations, pressure reducing valves, and other hardware are used. What connects these pieces of equipment are devices summarily called Remote Terminal Units (RTUs).  

Sometimes via radio, but most often through the cellular network, RTUs both send and receive messages from the master supervisory system, allowing control of the hardware they are attached to. Especially if the equipment plays a more critical role within the system, the RTU includes a battery and charger circuitry to continue operation if the mains power fails. Given that they operate underground in harsh environments, these batteries have to be as rugged as the whole water distribution network is resilient.