Reliable ventilation is vital for the health and safety of mine workers, to ensure particulates from diesel engines are adequately diluted, for example. For underground mining, ventilation operating costs are often a significant proportion of the total electrical-energy costs.
Drives are well-recognized for being the most flexible, energy-efficient and low-maintenance method for controlling mine ventilation fans. They are used to control the air flow of main ventilation fans on the surface as well as auxiliary ventilation and booster fans underground, and can be easily integrated into Ventilation on Demand (VOD) control systems. Both VLT® and VACON® drives incorporate a number of features that make them especially suitable for mine ventilation fan applications.
These ensure reliable operation of the fan even in abnormal operating conditions and the optimum use of energy including:• Automatic Energy Optimization (AEO) and Flux Optimization – to ensure the optimum magnetization of the motor at all loads and speeds and minimize motor energy consumption, the drive dynamically optimizes the voltage to the motor throughout the operating range. It automatically compensates for a motor’s falling power factor at partial loads. This improves the overall efficiency of the drive and motor combined at all loads and speeds resulting in lower operating costs.
• Direct Drive Fans - both VLT and VACON drives can be easily configured for optimum performance at the design point of the fan and then utilize the AEO/Flux Optimization function at all flow rates below that point. This ensures optimal energy efficiency at all loads/flow rates without the need for motor derating or unnecessary low speed or partial load motor over magnetization.
• Flying start - catching a spinning motor in both directions minimizes shock loads, mechanical stress and resulting wear and tear.
• Bypass frequencies - avoid resonance conditions that can occur at particular speeds by programming bypass frequencies in the drive.
• Auto Derate Functions - in mine ventilation systems, continuous operation of the fan is very important. For this reason, redundant fans are often used and some systems are designed on the basis that operation at reduced air flow rates is considered preferential to no air flow. This allows time for corrective actions to an abnormal operating condition to be implemented. All drives incorporate protection functions to protect the drive, the motor and the fan from overload conditions. These protection functions typically operate by tripping the drive and putting it into an alarm condition, resulting in the ventilation fan stopping. The VLT® HVAC Drive FC 102 incorporates a number of programmable features which enable continued operation of the fan, at reduced load (reduced air flow) if necessary, while giving a warning signal to the supervisory control system. These functions can be programmed to prevent the drive from tripping for as long as possible on conditions such as over temperature, excessive mains imbalance or complete loss of a mains input phase.