Electrical Controls/SCADA

Electrical Controls/SCADA

Overview Video


Overview Video

Electrical & Level Sensing

Can a lift station have two pumps that automatically alternate?

Yes, Romtec Utilities frequently designs lift stations that have two or more pumps. In typical use, the control panel will sequentially alternate starts between each pump so that the pumps will accrue equal runtime during the life-cycle of the lift station. This practice reduces some maintenance requirements for the pumps. Additional pumps also offer a measure of redundancy, providing backup should one pump malfunction.

Can you perform the lift station start-up using generator power?

Yes, but it always creates problems. Romtec Utilities has performed system start-ups on generator power but prefers that the system start-up take place on utility power in order to troubleshoot any problems by mirroring normal running conditions. If the utility power is incorrectly phased, the control panel and the overall lift station will not function. As part of the lift station start-up, Romtec Utilities ensures that the power has been connected in the proper manner to ensure that the pumps function as designed. Although Romtec Utilities provides built-in phase rotation protection, mixing up the power phases during install could run the pumps in the wrong directions or in a manner that is harmful to the mechanical systems.

Can you supply a generator for my pump station?

Yes, Romtec can provide a generator for your pump station. Romtec Utilities assists in selecting the correct generator for each application in terms of size, fuel types (i.e. diesel, natural gas, etc.), and compatibility with the control panel and electrical components. In addition, Romtec Utilities can also supply receptacles within the control panel to accommodate the use of a portable generator if that is preferred to one onsite.

How do soft starters compare with variable frequency drives (VFDs)?

Soft starters and VFDs are each used to reduce the in-rush current on the electrical utility during start-up of the pump station and/or electrical generator. They are necessary when the utility has restrictions on the horsepower of the machine being started or if there is a soft utility line that cannot handle the in-rush. Soft starters accomplish this function with basic controls and are much less expensive than VFDs. While more complex and more expensive, VFDs can match the speed of the pump(s) to optimize performance and offer more diagnostic capabilities. Constant level applications primarily use VFDs.

What is an automatic transfer switch (ATS)?

An automatic transfer switch is designed for switching of electrical loads between primary power and a standby generator. The switch monitors both power sources for stability. If the utility power becomes unstable, the transfer switch signals the generator to startup and then transfers power until the utility power source returns to normal.

Romtec Utilities uses ATS when a permanent generator is included in the design of the lift station. The ATS is sized for the required load of the system and can be service entrance rated to include a circuit breaker if necessary. The service entrance disconnect will interrupt excessive over-current from entering the system. This option can be expensive and generally it is more cost effective to locate a separate circuit breaker upstream from the ATS. Sometimes it is also necessary to design for a 4-pole system that switches the neutral. If the generator and utility are each required to be grounded neutral, then the transfer switch must have enough poles to switch the neutral. If the neutral is allowed to ground in both places, multiple undesirable current paths are created for the ground current to flow through. This situation can be dangerous if service work is being done on a line that is thought to be disconnected. If the generator system is completely enclosed within the rest of the system and is not separately grounded, a 3-pole system with a single solid ground can be used. This is cheaper than the 4-pole system.

The ATS is located in its own enclosed control panel that is sized depending on the required load. Service entrance rated ATS requires a much larger enclosure which must be accounted for in the layout of the control panels. Cummins offers a transfer switch with a 1200 amp rating that has an enclosure with dimensions of 90” tall x 39” wide, with a door closed depth of 27”. This enclosure weighs roughly 730 pounds and would most likely need to be floor mounted.

The ATS systems are designed to prevent generator startups from momentary power system losses or variations. They also maintain the generator availability for immediate reconnection after the switch back to utility power, in case of a reoccurring failure. This availability time is adjustable, along with many other time dependent options.

An automatic transfer switch is not normally used for a lift station design with a portable generator. A manual breaker is added so that the generator can be connected to the system and the power switched over.

What is an HMI?

A Human-Machine Interface (HMI) is the tool that allows the operator of a lift station to see data output and change parameters on the control panel. Typically an HMI is mounted on the control panel and consists of a 6”-10” screen with push buttons for the user. They range from black-and-white displays with limited push button controls to color displays with many layers of touch screen menus. HMI can also be referred to as OIT (Operator-Interface Technology) and was originally called an MMI (Man-Machine Interface).