We recently modernized a lift station’s control system from having its primary controller being electromechanical relays (connected to floats) to a Schneider Electric M340 PLC. This lift station is operated by a single pump and an across-the-line starter. The relay controls have served the operators well in terms of reliability. However, the aging infrastructure was not consistent with the overall digitization elsewhere in the wastewater network. This upgrade has allowed the operators to have more refined monitoring and control of this station as well as view their process data on their existing SCADA system.
Using an M340 (Figure 1) as the primary controller paired with a level element, we added the ability for the operators to adjust setpoints of the station as well as having a better idea of what is going on within the wet well. To ensure redundancy, we also included a backup float system to ensure the lift station operates in case the primary controller fails. The backup float system is comprised of a smart relay and a level float. The float is installed above the pump start level programmed within the primary controller. When the wet well level reaches the float, the pump is started and runs for a set period of time in order to drain the wet well. This configuration allows for operational redundancy as the backup float system is installed in parallel to the primary controller. Should one of the two controllers fail, the lift station will still operate. Operational redundancy is a big aspect to all lift station modernization projects. A lift station without continuous operation can get messy: wet wells can flood, and surrounding basements and water sources can fill with sewage, all resulting in unnecessary safety & financial implications.
Due to the station being small with no kiosk, the new panel was installed on the client’s existing private pole next to the wet well (See figure 2). As onsite monitoring was a desired feature, the HMI was installed on a swing panel within the front door.
Jason Marchese, P.Eng. PMP