Variable speed drives and centrifuges for zone 1 hazardous areas

Using a variable frequency drive (VFD) provides a standard solution to get the top performance of machines in many applications in the process industry. Today, there is no solution to install frequency converters inside the hazardous area. This limits the functionality and the ability for a compact solution to a Zone 1 installation. Due to the heat generated from the power electronics, many control systems have to be installed outside the hazardous area or alternative systems like hydraulic or gear drive are used. The new concept of a VFD can be installed inside the hazardous area and close to the machine, thus providing the solution to build compact skid mounted systems for Zone 1. The most important criteria regarding the explosion protection is the heat dissipation of the power electronics. This new concept is shown in an application with a VFD with 22,5 kW power. The PLC as well as the power electronics is built in one control panel which is used to control a modern decanter centrifuge with a torque dependant scroll drive. Via this system the centrifuge adapts itself to varying operating conditions such as solid loads and feed rate, resulting in optimum cake dryness. The paper will address how to cover the occurring ignition sources by measures in a practical manner, and how to implement them with a centrifuge using the VFD control panel.