Inverter drive saves £16,000 per year on a single motor

B Mason and Sons Ltd is thought to be the UK's largest manufacturer of precision rolled copper and copper alloy strip, and a major supplier to markets worldwide. In addition to continuous improvement of its plant and processes, the company has a commitment to responsible environmental practice. Recently this led to an energy audit in its strip plant, which quickly identified one major area, fume extraction, where substantial energy savings could be made.

The company has a number of furnaces, all of which use the same extraction and filtration plant. The plant is run from a 250kW motor, which, until recently, was operated at full speed seven days a week. However, this continuous operation turned out to be unnecessary, as not all furnaces are required to be in operation at the same time.

Deritend applied an energy meter to the 250kW motor and calculated that reducing the supply frequency by 10 per cent, or 5Hz, could reduce the cost of operating the motor by around 20 per cent. However, reducing the speed of the motor with its existing starting arrangement was not possible, so a decision was taken by Ray Ullah, B Mason's Maintenance Engineering Manager, to put the case for capital expenditure to uprate the system to inverter control, using as justification the calculated savings and projected payback data supplied by Deritend.

Motor refurbishment

Following project cost approval, the 250kW motor was removed and refurbished; the motor was rewound specifically to optimise it and protect it for inverter operation. This included the fitting of an insulated bearing. In addition, the motor windings were cleaned, re-insulated and fully tested. At the same time, Deritend personnel - working offsite so as not to interfere with production - installed the Siemens inverter and new contactors into an additional control panel and provided new cabling.

The total job, including motor refurbishment and panel assembly, was completed by Deritend during B Mason's nine-day shutdown to minimise disruption. The panel was installed by B Mason, and Deritend then commissioned the drive.

Subsequent to the installation, an energy meter was fitted to the 250kW motor and monthly readings taken. These revealed that the substantial savings calculated by Deritend were, indeed, being realised. Previous to the installation of the inverter system, the yearly running cost of the 250kW motor was £79,680. With the inverter system in place, and the supply frequency reduced by 10 per cent, this yearly figure has been reduced to £63,360, a saving of 20.48 per cent in energy costs. This is substantial enough to give B Mason a payback period of 12.5 months for the inverter-based system. The savings thereafter will be a boost to the company's profitability.

Ray Ullah states: "It has performed exactly as promised, and we are really pleased. Deritend told us that we could expect energy savings of around 20 per cent, and that is just what we got. They also handled the project really well in the pressurised nine-day period of our shutdown. Then they suggested other ways that we could save energy by using different drive belts and the like. All in all, a very successful project, and one that not only benefits us as a company, but also the environment, as it helps us to reduce our carbon footprint."