Plant & Works Engineering
Drives pump up the savings for water supplier
Published:  09 February, 2017

The UK’s largest water-only supply company Affinity Water, implemented a project with one of its framework contractors for replacement of the existing vertical turbine pumps with submersible pump sets manufactured by Bedford Pumps. PWE reports.

The complete project included these new submersible pump sets, riser pipework, HV power supply, transformers, MCC panels and pump controls. Danfoss variable speed drive systems, supplied as part of the MCC panels by system integrator Saftronics of Leeds, are now providing improved control and significant energy savings.

The Affinity Water pumping station that took part in the project has six raw water pumps, which were originally equipped with 3.3 kV medium-voltage motors. Four of them were controlled by fixed-speed starters, and two by variable speed drives. The operation of these pumps was approximately matched to the varying demand by the operators at the pumping station. They manually operated the pumps and trimmed flow into the works using one of the variable speed driven pumps as necessary to improve control.

The motors were however approaching the end of their service lives and the motor control gear was becoming unreliable. The starters and drives were also obsolete and spares were no longer readily available. In addition, all work on the motors and starters involved the use of specialist staff or contractors qualified to work on medium-voltage installations. Affinity Water therefore decided that a comprehensive upgrade was needed.

The company awarded the contract for replacement of HV systems, raw water pumps, MCC panels and pump controls to one of its framework contractors, who approached Saftronics of Leeds, an organisation with wide experience in designing and supplying control systems and switchgear for the water industry. After examining the requirements in detail, Saftronics put forward a solution based on modern 690V motors controlled by Danfoss VLT AQUA variable speed drives, which are optimised for pumping applications.

Danfoss drives were chosen for this project because these drives, when used in conjunction with active harmonic filters, provide very high efficiency.

Affinity Water agreed that the Saftronics proposal was the best and most cost-effective course of action and, as a result, the company produced two motor control centres, each equipped with three VLT AQUA drives rated at 315 kW and suitable for operation at 690 V. Back-channel cooling, with through-the-wall technology was used, which reduced the number of cooling fans needed in the motor control centres to eight, compared with the 24 that it is estimated would have been needed with ordinary cooling arrangements.

Each motor control centre was fitted with a Comsys 240A harmonic filter housed in a separate compartment. These filters were used to ensure that the new installation would be fully compliant with the harmonic limitation requirements of Engineering Recommendation G5/4. In addition, the pumps were equipped with 690 V motors rated at 300 kW and designed to have a maximum operating speed of 1254 rpm. All of the medium voltage equipment was removed.

Installation and commissioning of the new equipment at the pumping station went smoothly and the results were even better than had been anticipated. Particularly, because the pumps have been fitted with variable speed drives, it is now possible to accurately and automatically match their output to demand, which means improved operational efficiency, reduced wear and tear on the pumps, and significant energy savings.

Other benefits are greatly improved reliability and, if the need should ever arise, ready availability of spare parts. Furthermore, there is no longer a requirement to use specialist contractors for maintenance, as the medium-voltage parts of the system have been eliminated. It is also anticipated that the overall life-cycle cost of the new systems will be much lower than those of the old equipment.

Affinity Water are happy with the improvements made to this raw water pumping system with the incorporation of energy efficient Danfoss Drives and system design / manufacture by Saftronics.