Mentor dc drives improve steel throughput in South Africa 16 August 2011
Replacing analogue dc drives for energising electro-magnets with digital dc drives 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 on overhead cranes for transporting steel bars at numerous points on the ploant at eMalahleni, Mpumalanga.
Analogue drives were proving unreliable and destroyed numerous electro-magnets through over-excitation, causing excessive current flow.
Control Techniques' more closely controlled digital dc drives were chosen as the replacement technology, with CT Southern Africa providing a fully engineered solution.
The system comprises a 210A, 480V, four-quadrant Mentor MP dc drive for each electro-magnet, in conjunction with a freewheel diode that dissipates the back-emf into the magnet when de-energised – so providing a discharge path for the current.
Evraz Highveld specified the requirement to regulate current very accurately to prevent over-current damage to the magnets, and the drives have been configured in torque control mode.
The arrangement implemented ensures that the intensity of the magnetic field is maintained irrespective of ambient temperature.
As a result, damage from burning of the windings through excessive current has been completely eliminated, reducing maintenance and downtime and, effectively, improving average plant production line throughput.
Control Techniques Drives Ltd
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