by Dave Baston, Emerson Control Techniques

The installation of an AC drive with an advanced software tool has dramatically cut call-outs for blockages at an Irish county council pumping station. 

Pump control software has been installed to replace an AC drive at a pumping station at Kelly's Bay pumping station, Skerries in North County Dublin, Ireland. This new software cut maintenance callouts due to ragging and the fouling of the pump's impeller. These maintenance callouts have dropped from a weekly occurrence to just one call since the software was installed six months ago.

AC drive

The Maintenance Problems

Ragging is a long-standing nuisance that can eat up thousands of hours of maintenance in sewage pumping stations and wastewater treatment plants worldwide. At the Kelly's Bay pumping station, two variable speed drives controlled main and standby pumps.

“The pumping station would run for a couple of weeks, and then we'd get three or four call-outs in a week,” explains Fingal County Council's mechanical supervisor Jim McGuiness. “So, when it was time to replace one of the existing 15 kilowatt AC drives, Control Techniques' Drive Centre in Newbridge suggested that we had IPC Lite software loaded.

“It has worked extremely well. Before the software, we switched between the two pumps weekly to spread the load from a maintenance point of view. However since August, we have just run the one pump with the software and monitored its performance by telemetry. Maintenance costs have dramatically reduced.”

Call-outs for blockages to Kelly's Bay, a distance of approximately 11 miles, took a team of two an average of two hours each time, which is a significant maintenance burden and one that has now been significantly reduced. The pump now runs around the clock, with flow rates varying between 20 and 70 cubic meters per hour with the software providing early warnings of ragging and initiating cleaning routines when required.

The Solution

The software is an in-drive solution to ragging that provides early predictive detection of a problem as well as initiating a client-defined cleansing cycle. It measures on-board active current, unlike other systems that measure the motor's nominal current (a measurement that can give an error of 30 to 40 percent on the real torque figure). The software system measures real torque every millisecond. As soon as it registers a change in the active current profile, remedial action is taken to remove the potential blockage.

In the event of a blockage, the cleaning routine is initiated. The cleaning routine is user configurable via parameters and, in addition, a manual cleanse can be triggered by staff if required. To prevent repeated cleaning in the event of a major blockage, the software has a detection of successive cleansings (in this application five times), and a lock-out and alarm occur to indicate a fault.

The programming can be tailored to suit individual pumping stations in this case a level sensor was added to trigger the pump into high speed in times of flooding.

“We are pleased with the IPC system, and it has completely proved itself since its installation,” says Fingal County Council's senior electrical and mechanical engineer John Williams. “After checking our telemetry data over 12 months, it is clear that it has significantly reduced our maintenance costs. We are now looking at fitting IPC to the second riser and other problematic pumping stations are also under consideration.”

The software features advanced technology pressure and flow monitoring for surge prevention to protect expensive rising mains, while low flow detection and alarm checks site performance, since, even with clean pumps, low flow can indicate other problems. The software has been in trials for three years with UK water companies, as well as in companies in the U.S., Canada, Dubai and the Philippines.

Pumps & Systems, November 2010