Cleveland Potash

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					Variable Speed Control of Pumping in the Mining Industry DriveIT ACS 1000 Medium Voltage AC Drives for speed and torque control of 315 kW – 5,000 kW motors

Case Study

Mining industry
Cleveland Potash, United Kingdom Application: Pump, 168 KW

Problem
A four-pole, 168 kW, 3.3 kV motor drives a pump which controls the flow rate of a potash and brine mix brought to the surface. An eddy current coupling had been used to control the pump for more than 20 years but suffered regular breakdowns. It also used banks of potentiometers under manual control, a crude method that did not allow a fine adjustment of the flow, even when it was correctly functioning. It was not possible to deliver a consistent flow of potash/brine, resulting in erratic production schedules.

Solution
Cleveland Potash replaced the eddy current coupling by directly retrofitting to the motor an ACS 1000 medium voltage AC drive, which is optimized for direct fitting to existing and new medium voltage AC motors. While the ACS 1000 is typically applied to motors with powers of 315 kW and more, in this case Cleveland Potash saw clear benefits in retrofitting an ACS 1000 to their 168 kW motor. Direct retrofit without matching the drive to the motor was possible because the ACS 1000 features a patented sine filter. This, by producing a pure sine wave, avoids high voltage spikes and

Highlights
• Payback within six months • Reduced energy costs • Reduced maintenance costs • No new motor or cabling costs • Improved production efficiency • Reduced noise

Cleveland Potash near Whitby, has achieved payback in less than six months following the retrofit of an ACS 1000

ACS 1000 medium voltage AC drive

The existing pump and motor system now controlled by the ACS 1000 operates more efficiently and quietly than before

common mode voltage attacking and damaging the motor insulation and bearings. In addition, the ACS 1000 is a 12-pulse drive, eliminating the harmonics that might cause problems to the site’s electrical supply. Because of this, a three winding input isolation transformer was supplied as part of the overall project, but without major space implications: the small footprint of the ACS 1000 allowed both the drive and the transformer to be housed within the existing switch-room.

Additionally, energy costs have been substantially reduced because speed control of a pump using an AC Drive is more efficient than speed control using an eddy current coupling as shown in figure 1. Substantial cost savings were achieved at the outset because there was no need to purchase a new motor and hence no need to change the motor foundations. Additionally, there was no need to change the motor cabling and other electrical equipment. Even though the motor has a relatively low power for a medium voltage motor (168 kW), these savings, together with the continuing savings from reduced energy and maintenance costs, has enabled pay-back for the complete project within six months. The ACS 1000 is used in a closedloop control system, with signals received by the drive directly from the plant process control system. This provides more precise control over the pump flow rate than was possible with the manually operated Variac used in the previous openloop system. Control inaccuracies have been totally eliminated, with inevitable continuing energy savings. The whining noise normally associated with drives and large motors has also been virtually eradicated, with the system performing as quietly as with direct on-line running. This is due to the pure sine wave voltage and current to the motor delivered via the ACS 1000’s sine filter.

Background
Cleveland Potash has successfully operated the UK’s only potash mine for nearly 30 years, based in the heart of the North Yorkshire Moors. To mine a rich potash ore from a seam under the North Sea, two shafts descend 1,100 meters to a network of tunnels extending some eight kilometers out to sea. Up to 16,000 tons of ore, containing potash (potassium chloride), rock salt (sodium chloride) and other compounds, are extracted each day. The world potash market continues to expand, with potash used in fertilizer production, oil-rig processes, glass making and pharmaceutic manufacturing. Cleveland Potash also produces salt, supplied for winter maintenance to local government organizations in the UK and overseas.

Benefits
By installing ABB’s ACS 1000 standard medium-voltage AC drive on a 3.3 kV motor, Cleveland Potash has achieved significant improvements in production efficiency.

Key features & benefits
The ACS 1000 medium voltage drive offers many benefits as standard, including: • highest reliability and availability • high efficiency, > 98 % including sine filter and auxiliaries • lowest lifetime costs • small footprint and overall physical size • greatest transformer flexibility • high performance, through Direct Torque Control (DTC) • retrofit-ready, for fitting to any standard medium voltage squirrel cage motor, without derating • every drive fully factory-tested • two-day on-site commissioning • full compliance with international standards including EN (IEC), CE, IEEE, and the first medium voltage drive to be UL Listed.

Fig 1: The diagram shows the power requirement for different means of controlling the flow from a pump. Curve A Curve B Curve C Distance ∆P1 Distance ∆P2 Distance ∆P3 Throttle control Speed control with hydraulic or eddy current coupling. Speed control with AC drive system. Difference in power consumption between throttle control and speed control with AC drive system. Difference in power consumption between throttle control and speed control with hydraulic or eddy current coupling. Difference in power consumption between speed control with hydraulic or eddy current coupling and AC drive system.

ABB Switzerland Ltd Medium Voltage Drives 5300 Turgi / Switzerland Tel +41 58 589 27 95 Fax +41 58 589 29 84 Email mvdrives@ch.abb.com I-Net www.abb.com /motors&drives

3B HT 490 363 R0001, Rev. A Printed in Finland (0402-1000-1) libris


				
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posted:2/7/2008
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