Siemens soft starters for WBB Minerals

A KEY part of the ball clay refinery process at WBB Minerals’ East Gold Quarry in Newton Abbot, Devon, is a large dryer-pulverizer mill, which reduces the clay to a powder in preparation for further processing. The extreme nature of the starting load in this application meant that WBB Minerals had historically used a fluid coupling as a mechanical ‘soft start’ for the machine’s 168kW drive motor.

Although the fluid coupling was ideal for starting such large loads, increasing maintenance costs were placing a significant financial burden on the plant, so WBB’s engineering and maintenance departments where tasked with finding an alternative drive technique.

Barrie Drew, electrical engineer for WBB Minerals, explained: ‘The fluid coupling, while effective in generating enough power to start the dryer-pulverizer mill, was becoming increasingly costly to maintain. When changing the motor on the application it was necessary to pull the coupling off the shaft, which inevitably damaged the seals on the equipment and led to a £3,000 overhaul.

‘Replacement parts for fluid couplings are notoriously expensive, however we had no choice but to keep paying out as the dryer-pulverizer mill is such a key element within the refinery. Unfortunately, we were in a lose-lose situation; when the application faltered it not only cost us money to fix it, but was also costing us money for the time it was off-line.’

To overcome these issues WBB turned to Siemens Automation and Drives. Their solution was to replace the fluid coupling with an electronic soft starter.

Peter Costello, product manager LV at Siemens Automation and Drives, commented: ‘The task of replacing the fluid coupling was not an easy one, as there were several mechanical and logistical factors which needed to be taken into consideration. Special ratings had to be used to cater for the relatively high starting current during the acceleration of the motor.

‘However, the benefit of using an electronic soft starter is twofold; first, maintenance costs are virtually nil; and secondly, the starter provides better overload protection by monitoring motor temperature via thermistors, thus reducing the frequency of motor burn outs.’

Siemens supplied a 3RW44 electronic soft starter for the dryer-pulverizer mill, together with diagnostic software with a direct serial communication link to the starter.

Mr Costello continued: ‘Using the 3RW44 diagnostic software, the initial set-up was simplified. During starting trials the performance was closely monitored via online data on system temperature, current and speed. Settings were then adjusted to give the best overall performance.’

WBB Minerals say the investment they have made in new soft-start technology is now beginning to pay for itself, and the company plans to integrate the technology into other sites over the next two years.