Realizing energy savings in water processing applications using medium voltage adjustable frequency drives


Courtesy of Eaton Corporation

Why uptime and energy efficiency matter in water processing

Making sure that systems and processes are up and running while improving energy efficiency (and cost) is crucial in water processing applications. During the recent recession, federal and municipal budgets tightened, limiting access to capital across the United States. At the same time, increased awareness of the environmental and economic benefits of sustainable operations is driving changes in industry regulations. Consequently, water utilities have had to quickly adapt to evolving industry regulations and realities by adopting new technologies to control costs and reduce energy requirements. Best practices within the municipal water industry today involve energy conservation, as well as process efficiency and reliability, with a strong emphasis on long-term benefits.

For a typical water treatment plant, electricity accounts for approximately 80% of all water processing costs, and 30–35% of the plant’s operating budget. So, it is easy to see why power distribution and motor control practices have quickly migrated toward more efficient technologies. This is true for both new facilities and older processing plants, where equipment upgrades generate substantial efficiency improvements, reduce operating costs, and meet increased capacity requirements. Optimal solutions for new facilities and upgrades to existing plants strive to balance capital investment with long-term operating costs and equipment life.

Adjustable frequency drives control power, reduce cost

By matching power consumption to changing system requirements, adjustable frequency drives are increasingly relied upon to provide steady, efficient power for variable speed applications. Adjustable frequency drives also protect valuable motor and pump assets by controlling power and minimizing trauma placed on the system by starting and stopping pumps. As a result, municipalities can often calculate the return on investment for medium voltage adjustable frequency drives in terms of months, not years.

Adjustable frequency drives are among the most technologically sophisticated methods of motor control and have benefited from years of evolution in motor starting technology. Traditional across-theline starters apply full voltage to motor terminals, which can sometimes generate high inrush currents, causing stress to mechanical equipment. Reduced-voltage starting has evolved to help manage inrush currents and peak voltages, and is required by some utilities to prevent excessive voltage drops in the supply grid. Solid-state softstarter technologies have also emerged to further eliminate shock to mechanical equipment, as they reduce the load and torque applied to the motor powertrain during startup. Using SCR technology, soft starters provide a greater degree of control for reduced-voltage starting to help avoid motor coupling and shaft damage, prevent rotor and winding failure, and stop drive belt squeal and breakage. Additionally, reduced-voltage softstarters offer a wide range of current limit settings, providing greater control flexibility. For pumping processes, in particular, soft starters also help avoid “water hammer” in pipes by reducing line pressure so valves can close gently and prevent a surge wave.

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