The Challenges Facing Designers of Large Variable Speed Drives
* Table of Contents
1. Introduction 1
2. Background 2
3. Power Electronic Converters 4
4. Control of Motors Driving Grinding Mills in Mines 5 4.1. Load Commutated Inverter Drive 6 4.2. Cycloconverter 8 4.3. Slip Control Variable Speed Drives 9
5. Mechanical Problems of Large Grinding Mills. 11
6. Electrical Problems Caused by large Grinding Mills 12
7. Conclusion 13
7. References 14
Introduction
In the mining industry grinding mills are used to crush mined ore. To take advantage of economies of scale, more ore needs to be processed in-order for the mine to be more profitable. To process the ore mining operations have adapted large grinding mill drives in the megawatt power range. The power consumption of the large drives has forced designers to look at ways of increasing their efficiency.
Variable speed drives have been employed in large grinding mills used in mining. The use of variable speed drives has allowed for the efficiency of the drive to be increased and also allows for a more flexible grinding process. The grinding mill drive’s speed and torque is varied depending on the characteristics of the ore they are grinding and on the quantity of ore within the mill. This allows for the grinding process to be flexible to changes in the process.
The use of variable speed drives has also allowed for a single converter to be used for inching the drive during maintenance and for speed control. This feature is not possible with fixed speed drives. The variable speed drives used in the mining industry also have a functionality of detecting frozen charge. This feature is used to protect the mill from damages should the frozen charge drop as the mill is rotated from stand still.
This report investigates the challenges faced in the design of grinding mill drives for mining operations. The challenges investigated are control challenges, mechanical challenges and electrical challenges. In the report background information on the types of
1. Introduction 1
2. Background 2
3. Power Electronic Converters 4
4. Control of Motors Driving Grinding Mills in Mines 5 4.1. Load Commutated Inverter Drive 6 4.2. Cycloconverter 8 4.3. Slip Control Variable Speed Drives 9
5. Mechanical Problems of Large Grinding Mills. 11
6. Electrical Problems Caused by large Grinding Mills 12
7. Conclusion 13
7. References 14
Introduction
In the mining industry grinding mills are used to crush mined ore. To take advantage of economies of scale, more ore needs to be processed in-order for the mine to be more profitable. To process the ore mining operations have adapted large grinding mill drives in the megawatt power range. The power consumption of the large drives has forced designers to look at ways of increasing their efficiency.
Variable speed drives have been employed in large grinding mills used in mining. The use of variable speed drives has allowed for the efficiency of the drive to be increased and also allows for a more flexible grinding process. The grinding mill drive’s speed and torque is varied depending on the characteristics of the ore they are grinding and on the quantity of ore within the mill. This allows for the grinding process to be flexible to changes in the process.
The use of variable speed drives has also allowed for a single converter to be used for inching the drive during maintenance and for speed control. This feature is not possible with fixed speed drives. The variable speed drives used in the mining industry also have a functionality of detecting frozen charge. This feature is used to protect the mill from damages should the frozen charge drop as the mill is rotated from stand still.
This report investigates the challenges faced in the design of grinding mill drives for mining operations. The challenges investigated are control challenges, mechanical challenges and electrical challenges. In the report background information on the types of
References: [1] Barnes M., Practical Variable Speed Drives and Power Electronics, Elsevier, Oxford, 1st edition, 2003 [2] Briganti F, Eddy-Current Drives, http://www.drivesourceusa.com/news/index.html, Last Accessed on 18 July 2012. [3] Rodriguez J., Pontt J., Newman P., Moran L., Alzomora G., Technical Evaluation and Practical Experience of High Power Grinding Mill Drives For Mining Applications, Industry Applications Conference, Volume 3, 2003, pg 1629-1636. [4] Ahrens M, Gonser J., Technical and Commercial Benefits of Gearless Mill Drives For Grinding Applications, SME Annual Meeting, 2007 Denver, [5] Sen P.C, Principles of Electric Machines and Power Electronics, John Wiley and Sons, Canada, 2nd Edition. [6] Dr. Van Coller J.M., Variable Speed Drives for AC Machines-Elen7048, University of the Witwatersrand, 2012 [7] Pontt J., Rodriguez J., Valderrama W., Sepulvera G., Chavez P., Cuitino B., Gonzalez P., Alzamora G., Current Issues on High-Power Cycloconverter – fed Gearless Motor Drives for Grinding Mills, Volume 1, IEEE International Symposium on Industrial Electronics, 2003.