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Good things come in small packages01 November 2007The small footprint and low heat dissipation of Danfoss VLT ‘Aqua’ drives have solved a particularly knotty problem for Northumbrian Water during systems refurbishment work at its Lumley water pumping stationThe first of Danfoss’ new generation, high efficiency, high power FC series drives to be sold in the UK 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. 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 has to be pumped from the works. The pumps take their feed from the clear water tanks and the output from the works supplies two localities, Stonygate-Washington and Rainton-Mill Hill.
It is the pump on the Rainton-Mill Hill leg that has been refurbished by the addition of two new pumps, complete with variable speed drives, which will operate either as duty/standby or as duty/duty units. When a certain 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 online and the pair run in duty/duty mode. Flow rate is called up by analogue control from the PLC, with the drives feeding back a corresponding analogue output to confirm that the set speed has been 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 head 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, so 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 million litres per day. The pumps must also run for one hour each night to maintain water quality standards.
Lumley WTW is a modern facility featuring innovative architectural design and lighting arrangements. One of the features of the pump room is a very large south-facing window. On a sunny day the heat in this room, augmented by three heat-producing slip-ring motors, rises to above 40ºC, creating an ambient temperature problem for equipment installed in the pump room.
Beating off some pretty intense competition, Danfoss secured the order for two 200kW VLT ‘Aqua’ version drives. These were ordered by Labtec (Services), a company that has a framework agreement with Northumbrian Water for the design and supply of motor control centres (MCCs) and low voltage assemblies. Labtec was contracted to manufacture the MCC for Lumley Water pumping station and during the design phase of the contract, the company encountered space limitation problems. The smaller footprint of the VLT Aqua drive, compared with products from other drive manufacturers, proved an ideal solution to this problem.
Labtec requested prices for drives that would be suitable for powering the two 185kW pumps. The company explained that it already had quotations from other suppliers, but their drives would not fit the allocated MCC space. This was creating such a problem that the team considered siting the drives at a motor control centre located elsewhere in the plant - with severe cost implications. Colin Corner, Labtec’s technical director was initially sceptical.
“We thought that the 1,900mm height available within the MCC was insufficient for drives of this power but the compact dimensions of the VLT Aqua 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 Aqua drives were specified for a maximum of 45ºC with no de-rating, meeting the spec for the frequently hot pump room.
“Two drives were ordered as duty/standby units, and to meet the client’s specification additional cooling was provided. Rittal door-mounted chillers were fitted to maintain a low ambient temperature within the cubicles, avoiding the more expensive option of air-conditioning the pump room as a whole. 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 the other drives we considered, and this 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 was simple and fast, and we found the drive keypad in particular, 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.
Danfoss drives are currently under consideration for further projects at this, and other Northumbrian Water plants. Contact Details and Archive...Most Viewed Articles... |
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