At its plant at Whittlesey, Peterborough, McCain Food produces 30 tonnes of frozen chips per hour. The company, however, was looking for further ways to reduce its energy consumption and costs and decided to replace its old refrigeration facility with modern equipment. The on-site cold store, which operates 24/7, accounted for 60% of the site electrical loading. The company also wanted to get better control of the refrigeration plant and reduce the potential impact of harmonics.
For the solution, McCain has adopted ABB low harmonic variable-speed drives to cut its site load from 7MW to 6MW.
Paul Derbyshire, McCain’s electrical, control and automation engineer, said: “Although we had no known issue with harmonics on site before the project, one of our main motivators was not to generate any harmonics from the installation of such large drives.”
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, especially fifth and seventh harmonics. Typical current distortion can range from 30 to 50% in total. In an ABB low harmonic drive, the use of the motor control platform, direct torque control (DTC), together with a low pass filter, suppresses the current harmonic content, giving a distortion of less than 5%. The resulting clean sinusoidal current will therefore cause little or no distortion on the network voltage waveform.
Benefits include direct connection to the network, with no complex multi-winding transformer required and no need for external filter equipment. The drives exceed the requirements of EN 61000-3-12 and IEEE519 and offer genuine unity power factor with no compensation needed.
The new refrigeration plant cut the number of compressors from 20 to seven. To run the compressors, ABB installed seven variable-speed drives, with ratings ranging from 350 to 650 kW.
Overall, the new refrigeration plant using ABB drives cut the site loading by around 1 MW. They have also given the company the ability to over speed the motor to get more refrigeration capacity.