Articles & Case Studies

Good things come in small packages

Posted: Friday 4th January 2008

The first of Danfoss’ new generation, high efficiency, high power FC series drives to be sold have been supplied to Northumbrian Water’s Lumley Water Pumping Station in the North East of England for the refurbishment of the Lumley – Rainton booster pumps.

The water for the treatment works is pumped from the river Wear at Lumley Riding and, after treatment, is stored in two clear water tanks. The water treatment works has no gravity supply and all water must be pumped from the works. The output from the works supplies two distinct localities, Stonygate-Washington and Rainton-Mill Hill. It is the system on the Rainton-Mill Hill leg that has been refurbished by the addition of 2 new pumps, complete with variable speed drives, that will operate either as duty / standby units or as duty / duty. When a specific flow is requested from the PLC, one pump set may be sufficient to meet that demand but if the PLC calls for a flow rate beyond the capability of the single pump, then the second pump set comes in and the pair run as duty / duty. Flow rate is called up by analogue control from the PLC with the drives feeding back a corresponding analogue output signal to confirm that set-speed is achieved.

The water for Rainton-Mill Hill pumps directly into a trunk main and is buffered by Mill Hill reservoir. An inlet pressure of 2m is supplied to the pump from the clear water tanks and the duty pump is required to produce a bulk flow into the distribution system, rather than feed demand directly, therefore a system curve has been developed by Northumbrian Water. These pumps are used as a secondary source for Wear Valley and the Southern GWS. The flow required from the pumps is used to make up any shortfall between demand for the water available from Wear Valley and the GWS, zero to 16 Mld. The pumps must also run for 1 hour each night to maintain water quality standards.

Lumley WTW is a modern facility and one of the features of the pump-room is a very large south-facing window. On a sunny day, the heat in the pump room, exacerbated by three heat-producing slip-ring motors, rises above 40oC, creating an ambient temperature problem for equipment installed in the pump-room.

Against stiff competition, Danfoss secured the order for two off 200kW VLT® AQUA versions. The drives were ordered by Labtec (Services) Ltd who have a framework agreement with Northumbrian Water for the design and supply of motor control centres and low voltage assemblies. Labtec were contracted to manufacture the MCC for Lumley Water Pumping Station and during the design phase of the contract ran into space limitation problems. The smaller footprint of the VLT® Aqua drive compared to other drive manufacturers proved the ideal solution to the problem.

Labtec requested prices for drives suitable to power the two 185kW pumps and explained that they already had quotations from others but their drives would not fit into the allocated MCC space. This was creating a problem to the extent of demanding relocation of the drives to an MCC located elsewhere on the plant, with severe cost implications. Initially, Colin Corner, Technical Director of Labtec was sceptical.

“We thought that the 1900mm height available within the MCC was insufficient for drives of this power but the compact dimensions of the VLT® AQUA Drive meant that even with air space requirements above and below the drives, they would fit comfortably into the enclosures with room to spare. It was a bonus that the AQUA drives are specified for a maximum of 45OC with no derating, meeting the spec for the frequently hot pump-room.”

“Two drives were ordered as duty / standby units, and to meet the client’s specification an additional cooling solution was provided. Rittal door mounted chillers were fitted to maintain a low ambient temperature within the cubicles, avoiding the more expensive solution of air-condition the pump room as a whole. The Rittal chillers work on the same principal as car air-conditioning units, drawing warm air into the units, condensing it then refrigerant enables much cooler air to be pushed back into the cubicles, offsetting the heat created by the drives. During commissioning and proving in May and June we carried out extensive monitoring and established that the air temperature in the pump-room was 49oC average. The chillers provided air internally at 8OC and with the drives running, the ambient inside the cubicles rose to no higher than 38OC.”

“The high efficiency of the AQUA drives meant they created less than 5kW of heat each - 3kW less per drive than that of others considered, and helped to maintain the temperature below maximum limits. Energy saving is a major aspect of this project and the drives provide continuous feedback of energy usage both to recorders and on the keypad. Overall programming of the drives was simple and fast and we particularly found the drive keypad very user friendly.”

Early indications are that efficiency has been greatly improved but longer term monitoring over seasonal variations will be required to provide an accurate picture of annual energy savings and carbon reductions. Since this order was taken, at the request of Northumbrian Water, Danfoss has carried out a further drives seminar at a local cricket ground, introducing the drives to Northumbrian Water’s contractors, consultants and framework suppliers. As a consequence, orders have also been placed for 150% torque rated, positive displacement pump drives where the performance of the drives rather than their compactness was a critical consideration and Danfoss drives are currently under consideration for further projects at this and other Northumbrian Water plants.

Tel:- 0870 241 7100
Fax:- 0870 241 7150

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