A custom variable frequency drive (VFD) from Eaton was recently installed at the Town of Mooresville’s Water Treatment Plant in Mooresville, North Carolina.

The VFD fits within the plant’s space constraints and has been keeping its 800-hp pumps moving efficiently. To avoid redundancy between the town’s new and old plants, and to maintain usability of its pump investment, the public water utility looked to Eaton to get the 800-hp pumps up and running without affecting the operation or efficiency of the old plant.

In 2008, the Town of Mooresville built a new water treatment plant to meet growing demand. Initially rated to pump 12 million gallons/day, the plant was designed to scale to 36 million gallons/day if needed. However, when demand did not rise as quickly as expected, the plant’s two new 800-hp pumps sat idle for several years.

Redundancy is important in water treatment – if one pump or plant goes down, having a backup is imperative to keeping water flowing to customers. With the new plant operational, water flow from both the old plant and the new plant merged in the main pipes. When the town’s new 800-hp pumps ran, however, the older plant’s pumps could not create enough pressure to overcome the increased pressure in the main pipes, significantly decreasing the efficiency of the old plant.

Without regular use, pumps run the risk of rusting out and becoming unusable, so, in order to preserve the town’s investment, the plant looked for options to get the 800-hp pumps up and running without affecting the operation or efficiency of the redundant plant.

The new SC9000® EP medium voltage adjustable frequency drives increase energy efficiency in the plant with a noticeable reduction in power usage. The drives control the pressure from the high-service, 800-hp pumps, allowing the new and old plants to work in tandem – and preventing the new pumps from rusting away due to disuse. The VFD system controls the water flow, allowing it to flow at a lower rate of speed, and making it possible to use both the new and old water treatment facilities.

Featuring an encapsulated powerpole and modular inverter design, the drives also help reduce downtime during routine maintenance. In addition, the encapsulated powerpole inverter with heat pipe technology reduces overall equipment size and helps protect sensitive electronic components in the harsh plant environment.

In order to accommodate the VFD, Eaton designed a compact integrated control gear solution that close-couples the new drive with the plant’s existing Ampgard medium voltage motor control. By integrating the VFD and motor control with a bus connection, the new drive could be installed without needing to move expensive cables and equipment. The team’s design kept the VFD in one room with no modifications and tied it back to the plant’s existing communications system.

“By designing a compact integrated control gear solution, we were able to keep the VFD in one room with no modifications and tied it back to the plant’s existing communications system,” said Jerry Wang, project engineer, Eaton. “Building on existing infrastructure to meet capacity and redundancy needs, the Eaton team provided a system that helps ensure reliable water treatment services for the Town of Mooresville’s customers.”

Eaton’s SC9000 EP medium voltage adjustable frequency drive was installed in July 2015 and has performed well since, with no issues to date.

“As a representative responsible to the citizens of Mooresville, we wanted to find a way to implement the equipment we had on hand,” said Barry McKinnon, public utilities director, Town of Mooresville. “Eaton’s variable frequency drive solution has performed excellently with no problems, helping us ensure water treatment services for our customers.”

For additional redundancy, the team added lock-outs to the 800-hp pumps so that the pumps can run off of the SC9000 EP drives and be backed up with soft starters.

To learn more about Eaton’s VFD offerings, visit www.eaton.com/SC9000.