The Problem

At the Lafarge Quarry the motor was started using a Soft-starter, which was drawing up to 5 times full load current. Obviously this is a huge waste of energy but as is the way with such high
consumption machinery, it was deemed necessary, even best practice. However, running the process in this way did result in other problems around the site with different equipment being affected by voltage dips.

Sentridge’s Solution

Sentridge Control applied AC Variable Speed Drive (VSD) technology to the quarry’s gravel plant, with impressive results and have helped reduce the running costs of a 160kW Metso Cone Crusher at the Lafarge midlands quarry, and brought the quarry closer to it’s target of reducing energy consumption. By applying VSD technology in the right ways to the crusher, the plant was able to significantly reduce demand on the energy supply when starting.

Glen Hickman of Sentridge says “Softstarters do provide a smooth mechanical start but can draw high current when activating and they also produce less torque on start-up”.

Following a Free Energy Audit the Sentridge team reported their findings and set about removing the dated technology and installing modern AC Variable Speed Drives.

The results? Impressive energy reductions meaning that the quarry is saving thousands of pounds and hundreds of tonnes in CO2 emissions every year.

The Full Story

After talking to the quarry about the possibilities of reducing energy consumption, we arranged a free energy audit to establish what exactly the main consumers were in the first place and to see what savings could be made through upgrading dated equipment. Energy comparisons are made at the incoming supply to the process, measuring the original controls and then with applied Sentridge VSD control.

This allows the motor to have an infinitely variable flow or pressure which is matched precisely to the demand of the process. After the application of the variable speed drive the speed of the motor is varied to the required level and thus saves energy. In this case it was the use of Soft-starters as Glen Hickman explains: “Traditional slip-ring motors and starters were ideal as they produced higher starting torque with lower currents, typically 1.5 to 1.8 times FLC, but do not provide any variable speed control. They are becoming increasingly more difficult and costly to obtain and run than a conventional motor. The AC drive can overcome many of these problems, providing High Torque at

Start, lower starting currents (typically 1 to 2 times FLC), smoother starting, variable speed control and importantly energy saving. Energy savings are achieved by precisely matching the motor loads and accurately controlling the output voltage of the drive to the required levels. This can provide off-load energy savings of up to 20%. In addition product quality is better controlled with more information on the crusher loading, torque and power being closely monitored by the drive”.

The Results
Reductions were made in the following areas:

• Huge energy costs
• Plant noise levels
• Maintenance costs due to soft start control
• Mechanical stresses in the system
• Belt wear and replacement costs
• Reliable process

For more information about how you could take advantage of a free on-site energy survey and to start saving today, please don’t hesitate to call us on 024 7655 3303.