Electricity + Control January 2019

DRIVES + MOTORS + SWITCHGEAR

• Remote IO – Flex IO. • Profibus as main Fieldbus.

and the other to the delta winding to reduce harmonics. • Additional controllers added to be able to run each of the parallel drives separately – level of redundancy. • Speed measurement – encoders on the mo- tors, encoders on the idler wheels to measure rope speed. • The aim is to keep the rope speed identical, as the liners wear, and to do load sharing be- tween the drives. • Speed modes – jog (forward only), crawl, and run. • The speed matching solution is realised by us- ing variable speed drives and there will be no mechanical coupling between the two steel cables (north and south ropes). Control solution A single SCADA station will be used to control the plant. A main desk is installed as a maintenance location and to provide redundancy if the SCADA stations fails. There are four modes of operation: automatic mode, manual mode, desk mode and local mode. The standard operation when a run is selected is to run the conveyor at crawl speed until the take- up at the tail has occurred and then accelerate the conveyor to the selected run speed. The drives will monitor the line speed of each rope by using the encoders on the idler wheels, this will be used to do speed matching. The drives will also do load sharing by monitoring the torque of each drive. Equipment to be used for the control is as follows: • CTI PLC / Citech SCADA.

There are four modes of operation: automatic; manual; desk; and local.

• Remote IO in each MCC starter and MV feeder. • Main desk with Operator Panel (CTI) with standard pushbuttons for common functions. Benefits of the new system • Safety – anti roll back, 400% braking capacity of each drive wheel with dual channel system and high speed brakes. • Expect more even liner wear with load sharing and speed matching. • With the drive doing dynamic braking there is reduced wear on the brake pad and the brake path. • Easier fault finding – new MCC, MV panels, PLC software. Conclusion The safety requirements of the customer (braking, anti roll back and safety barrier) will be completely implemented. The speed control and soft starting of the conveyor will be tested on site and be com- pletely implemented. A fully redundant system was never envisaged but a level of redundancy will be achieved with the following elements of the system: • Drive transformers – one active/one installed in stand-by. • Change-over panels to connect the drives to the other drive transformer. • Run 50% conveyor capacity by using only one motor winding, using the additional drive con- trol units and only one converter block per drive. Acknowledgements The author would like to acknowledge the follow- ing people: • Bannister Erasmus – Tech Edge (Design of me- chanical solution) • Roberto Robbetse – South32 Wessels Mine (Customer) • Keith Milford – JVL Industries (Design assis- tance) Resume John Proctor has a BSc Electrical Engineering de- gree from the University of Cape Town. He has an MDP in Project Management from UNISA, and has worked at Siemens Ltd for 30 years.

Figure 4: Factory acceptance setup.

16 Electricity + Control

JANUARY 2019