AC Motors Improve Sludge Pump Reliability

Scottish Water has replaced the ageing DC pump drive motors of three large sludge pumps at one of its wastewater facilities with matched W21 high-efficiency AC motors and CFW-09 drives from WEG. The DC motors were employed on Whitehead and Poole piston ram pumps that are used to transfer sludge from the Laighpark wastewater treatment site, which serves around 150,000 people in the Paisley area of Glasgow, to Shieldhall wastewater treatment plant.

They had been installed for some years, providing the high torque at start-up necessary for the pumping operation, and the facility for variable speed control of the pumps via a simple potentiometer. Because the capacity for storing sludge at Laighpark is limited, transfers to Shieldhall are made daily. This places a premium on the reliability of the two front-line motors - the third is a duty stand-by - which are generally called upon to operate for six hours a day. This was not a problem until recently, when the age of the motors starting causing concern.

Apart from questions of ongoing motor reliability, spares were becoming a particular problem, especially so in view of the repeated failures of the DC control equipment that were being experienced. In view of the frequent failures, the operations team leader submitted a request for the EandM technical support to investigate. It was determined that all three of the DC machines would have to be replaced in order to restore higher levels of reliability to the sludge pumping operation.

For the supply of the replacement motors, Scottish Water turned to Brammer, with whom it has a framework agreement. This agreement means that Brammer actively works on Scottish Water's behalf to deliver the most cost-effective, reliable and suitable products across a wide range of categories, including gearboxes, motors, inverters, power transmission, bearings seals, lubricants and many other products. 'Scottish Water was looking for a solution that delivered the flexibility to control the pumps in the manner that they always had,' said Walter Bryce of Brammer.

'However, these benefits had to be delivered in a package that offered the best competitive price and the longest possible warranty. 'Following consultations, we were able to deliver all this with a matched motor and inverter drive package from WEG,' he added. The WEG motor drive package provides improved flexibility in the operation of the pumps. It comprises three W21 200kW EFF1 high-efficiency motors and three CFW-09 frequency inverters.

The motors are effectively matched with the drives because they have demonstrated the highest levels of energy saving and reliability, which WEG covers with its three-year warranty. Brammer supplied the WEG motors, drives and control gear to a local panel builder in Kilmarnock. The drives and control gear were built into control cubicles and then installed on site. An engineer from WEG subsequently visited the Laighpark site to assist in the commissioning of the project, which was completed in a day, minimising any disruption at the facility.