McCain’s cuts refrigeration costs with low harmonic drives 06 December 2013

McCain Food's plant at Whittlesey, Peterborough, has reduced its site load from 7 MW to 6 MW, following installation of new refrigeration plant powered by ABB low harmonic variable-speed drives.

The plant – which is the UK's largest chip factory, producing 30 tonnes of frozen chips an hour – upgraded its on-site cold store, using the drives to reduce energy consumption as well as to improve control and reduce the potential impact of line harmonics.

Paul Derbyshire, McCain's electrical, control and automation engineer for McCain Central Engineering GB, explains that the refrigeration plant operates 24/7 and accounted for 60% of the site electrical loading,

"We were looking for the best drive for this application and investigated several solutions from a number of manufacturers," states Derbyshire.

"We found that nothing gave the same performance as ABB active front-end variable-speed drives. There is no interference on the line and they do not need filters to cut harmonics, as other drives do."

Derbyshire also says that, while there was no known issue with harmonics on site before the project, one of the project's goals was not to generate any by installing what would have to be large drives.

In fact, the new refrigeration plant cut the number of compressors from 20 to just seven, with ABB installing seven variable-speed drives to run them, with ratings ranging from 350 to 650kW.

Derbyshire confirms that the new refrigeration plant cut the site loading by around 1 MW. "[The new drives] also gave us the ability to over-speed the motor to get more refrigeration capacity, which we cannot do with traditionally-controlled refrigeration plant," he says.

Since the drives were installed at the plant, more have been installed at other McCain Food's plants globally and Derbyshire says the company says it is currently looking for other applications where ABB drives could bring benefits.

ABB explains that in a conventional frequency converter, with a six-pulse diode bridge as a rectifier, the network side current is not sinusoidal and has significant harmonic content – particularly fifth and seventh harmonics.

Typical current distortion can range from 30—50% in total, whereas on ABB low harmonic drives, direct torque control (DTC), together with a low pass filter, suppresses the current harmonic content, giving a distortion of less than 5%.

Other benefits include direct connection to the network, with no multi-winding transformer required and no need for external filter equipment.

In fact, the drives exceed the requirements of EN 61000-3-12 and IEEE519 and offer genuine unity power factor with no compensation needed.

Brian Tinham

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