It has been said that water is the oil of the 21st century, making the continuous operations of today’s water treatment facilities of great importance. Uninterruptible power supplies (UPSs) at these facilities are therefore essential, as these protect process controllers and monitor and control the facilities from power outages.
According to Ravi Saman, water and wastewater manager at Schneider Electric South Africa, the raw material needed to produce drinking water comes from different sources, such as springs, aquifers, rivers and oceans, and appropriate technologies to treat each have to be used. “The available space and the volume of water to be treated also determine the technical choices. In all cases, however, the required water quality has to be reached and proved in accordance with regulations and the authorities.”
Systems availability
Both the automation system and the electrical network at a water treatment plant must first be studied in order to provide high performance and a high level of availability. The solution includes software and hardware architecture with redundancy at all levels.
“A high level of availability affects power as well as automation and is requested for all parts of an application identified as being critical. It may include redundancy for power architecture, standby generators, UPS, motor control, programmable logic controller (PLC), communication and scada.
“Different circuit configurations can also be selected and are, in increasing order of power availability, radial single feeder, two-pole configuration (secondary selective) and double-ended power supply (primary selective),” says Saman.
The implementation of back-up generators is very common in water treatment plants where water distribution cannot be interrupted for periods longer than a few minutes. “No instantaneous takeover is necessary as buffer tanks are generally present. Automatic transfer switches are naturally associated with generators for rapid takeover and smooth switchback to normal supply,” adds Saman.
Coordination is required
“Protection coordination is a key aspect for improving supply continuity. Two examples are discrimination between functional units so that a problem on a grid does not stop biological treatment for instance, and coordination of motor protection and control minimises downtime.”
Schneider Electric South Africa’s solutions for high availability in water treatment facilities are mainly focused on the following three levels:
Scada: On the scada side, Schneider Electric South Africa offers seamless, integrated and scalable redundancy. This flexible redundancy can be enlarged to avoid not only network errors, but also PC hardware faults, with a resultant highly optimised and available solution.
Industrial Ethernet: has proved itself over the years as being the reliable industrial standard. It provides the solution for communication architectures requiring high levels of availability. Communication can easily be adjusted to the required level of availability such as redundant media or network interfaces, self-healing fibre-optic rings and communication backups.
Control doubling a PLC: this provides a highly optimised solution that avoids the negative effects and process downtime caused by problems at the control level. In the event of an error, there is an automatic ‘bump-less’ switchover between the primary and the standby PLC – both, are connected by a dedicated high-speed Ethernet link. Duplicating the I/O level, along with the corresponding sensors and actuators, can increase the availability level of the control system.
“In water applications, the environment is sometimes polluted and may have negative impacts on the ageing of the electronic components used,” concludes Saman. “This results in unexpected downtime and higher maintenance costs. However, based on extensive field experience, Schneider Electric has developed a special protection process (conformal coating) to improve service life in such aggressive chemical and corrosive environments.
“Water is a planetary resource that concerns all countries. Strong global players are present but it is still a local market and Schneider Electric South Africa has all the solutions this sector needs.”
For more information contact Jacqui Gradwell, Schneider Electric SA, +27 (0)11 254 6400, [email protected], www.schneider-electric.co.za
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