Intelligent Sump Pump Control

Sump pump control is one of the simplest automation systems there can be, in theory. Water flows in, the level rises to a switch point, and a pump turns on to empty the sump.  But then if the water is actually sewage, with occasional high volume flows in storm conditions, and good pump practice means you need to minimize the number of pump starts, even out the pump wear, plus prevent any overflow under single pump failure conditions, while also minimizing pump energy consumption costs, then the control system can get more complicated. Then add some further intelligence that mimics the actions often required during regular inspections of the sump, to clean it out, and automatic features to detect when the pump efficiency is reduced because the entry is jammed with solids or rags or solids build-up, and initiate a flushing out or other procedure to clear the blockage, and the programme features become quite complex.

Whilst originally pump control schemes to address these problems were developed on the PLCs used to control wetwell pumping stations, industrial motor drive suppliers like ABB and Control Techniques have also been addressing such problems, and both have come up with configurable software packages (both named “Intelligent Pump Control”) for optional use on wetwells, using variable speed pump motor drives. Using these techniques has enabled significant savings in maintenance and cleaning costs at sites where pump ragging has been a problem, and as an additional benefit, higher pump efficiency has been shown to produce energy savings in normal running, calculated to be up to 15%.

Control Techniques IPC

Over several years the Control Techniques (CT) Intelligent Pump Control (IPC) system has built up a successful base of applications with several of the major UK and Ireland water companies, as well as in installations in USA, Canada, Dubai, and the Philippines. “IPC is unique in that it measures ‘live’ active current in real time, on-board the drive (Impeller true torque component every millisecond)” explains Control Techniques UK Water Manager, Brian Redpath. CT suggests that competitor’s systems have measured the motor’s nominal (total) current – a measurement that includes the magnetic field current and can give an error of up to 30-40% for required effective monitoring of impending ragging.

Redpath continues: “As soon as IPC sees a change in the active current set profile, an automated cleansing cycle is instantly initiated to clear the pump impeller.” The active current profile for each pump is established during commissioning, and this sets the standard against which future performance is compared. Any ‘out of profile’ performance is instantly detected, giving an early warning indication of ragging. The cleaning cycle involves a slow ramp down, and a period of reverse flow. As well as detecting and preventing ragging, IPC systems also provide several other intelligent performance optimisation functions, such as surge prevention to protect rising mains, and wear monitoring of pumps. The system also detects dry running fault conditions.

The Control Techniques (CT) IPC software fitted to a CT Commander SK AC drive at a pumping station at Kelly’s Bay, Skerries in North County Dublin, Ireland has cut callouts from ‘ragging’ from a weekly occurrence to just once over a period of six months. At Kelly’s Bay, two variable speed drives control 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 15kW AC drives, Control Techniques Drive Centre in Newbridge suggested that we had the IPC software loaded.  Since then we have just run the one pump with the IPC software and monitored its performance by telemetry: maintenance costs have dramatically reduced.”

Graeme Moore, Senior Project Manager, Innovation & Technology for Scottish Water, recently presented the results of an evaluation of the CT IPC at their Levenhall Sewage Pumping Station, where blockages and ragging needed to be dealt with two to three times each week: the station has four foul pumps and three storm pumps. Within the wastewater industry, an estimated three quarters of all pumps are over-sized by more than 20% to provide a ‘factor of safety’ in the design, according to the British Pump Manufacturer’s Association.  The use of variable speed drives can be used to reduce the energy used by over-sized pumps, and reduce hydraulic system losses. The use of VSDs can play a substantial role in energy reduction by bringing the pump in line with the consented flow and reducing friction (energy) losses in the system.  The ‘soft start’ functions can also increase the life of components, such as bearings and seals. Levenhall uses circa £28k per annum of electricity and requires circa £15k per annum of operational interventions, to deal with ragging, blockages and pump trips. The installation of a VSD using IPC at Levenhall on one of the pumps produced an average running current on the VSD equipped pump of 15% to 30% less than the other pumps, plus no blockages. Peak operating currents were reduced by over 40%.

ABB Drives IPC

The ABB Intelligent Pump Control (IPC) software was launched back in 2006. The techniques have been refined in many applications, some of which are quoted below. New drives have been specifically developed for the water industry, and this software is specifically included in those: for other industrial drives the IPC is now a standard option.

ABB agree that the total current is not a suitable parameter for monitoring for pump blockage or reduced flow, and ABB monitor the speed and torque over the pump performance curve: they use “Direct Torque Control” (DTC), which is analogous to the CT “active current”: the two types of VSD use different approaches to speed control, so they are not exactly comparable.

The ABB IPC for water applications allows the selection of various schemes for pump reverse running, adjusting time and speed, since in some conditions impellers are supported by a nose nut. Also a blocked inlet to a pump might cause underload conditions rather than an excess of current, and the IPC allows a pump reverse cycle to clear such a blockage. A patented additional feature allows the IPC to make a calculation of the effluent flow rate, in normal flow conditions, using data from a pressure transmitter. The user can configure other specific functions, for individual site conditions, using the Solution Program Controller (SPC) blocks available from a pre-configured library.

The ABB IPC system was installed on a six pump sump used at the Severn Trent  (STW) Wanlip sewage treatment works, where four direct-on-line pumps and two variable speed drive (VSD) controlled pumps were showing low flow rates that appeared to be caused by ragging. The anti-jamming features in the IPC sorted the problems. Graham Drabble, the STW Capital Liaison Technician for Wanlip said: “As well as curing the flow problem, the new installation allows us to achieve our pumping requirement using only two or three pumps instead of all six, achieving an energy saving of approximately GBP100k per year.” Similar costs were saved on pump maintenance and cleaning at a four pump sump in the STW Worcester sewage treatment works, where the existing ABB 132kW industrial drives, supplied complete with filters to reduce harmonics, were given a simple upgrade to add the IPC software. Here the reverse running speed had to be restricted, because of the fibre content of the effluent, which needed to be unwound slowly.

In another installation for Anglian Water at its Stanbridgeford wastewater treatment works in Bedfordshire, two pumps using a 55kW ABB drive were equipped with IPC: the lack of ragging and the subsequent increase in operational time mean that the pumps can run at a lower speed or for less time and still achieve the desired pumping volumes, leading to energy savings, according to Adam Brookes, of Anglian Water’s Innovation Team

Redpath from CT comments: “Every site is different, and IPC is totally flexible, able to be configured to meet customer’s applications.  It works equally effectively on wet and dry well installations, and also treatment works pumps”. ABB would agree.

 

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