Improving steel mill throughput with DC drives

16 August 2011

The replacement of analogue DC drives with digital DC drives from Control Techniques for the energising of electro-magnets at Evraz Highveld Steel and Vanadium in South Africa has reduced downtime and increased throughput on a steel bar production line.

The electro-magnets are used on overhead cranes at numerous points in the production process for the transport of steel bars.

Analogue DC drives had proved to be unreliable and destroyed numerous electro-magnets as a result of being over-excited, causing excessive current flow. It was decided that a changeover to more closely controlled digital DC drives was the answer and Mentor MP DC drives from Control Techniques were chosen for the task.

The Control Techniques solution comprises a 210 amp/480V, four-quadrant DC drive for each electro-magnet, in conjunction with a freewheel diode that dissipates the back-emf into the magnet when the magnet is de-energised, providing a discharge path for the current.

Evraz Highveld needed to accurately regulate the current to prevent over-current damaging the magnets and the drives are configured in torque control. The arrangement ensures that the intensity of the magnetic field is maintained irrespective of ambient temperature.

Mentor MP is designed with future requirements in mind, with full system integration, three slots for option modules, an in-built field controller and very user-friendly software using real units.

As a result of the replacement of the analogue DC drives with Mentor MP units, damage from burning of the windings through excessive current has been completely eliminated, reducing maintenance and downtime and, effectively, improving average line throughput.

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