There mainly 2 type control panel with Explosion proof (EX)
1) Flameproof (EX d): Equipment construction is such that it can withstand an internal explosion and provide relief of the external pressure via flamegap(s) such as the labyrinth created by threaded fittings or machined flanges. The escaping (hot) gases must sufficiently cool down along the escape path that by the time they reach the outside of the enclosure not to be a source of ignition of the outside, potentially ignitable surroundings. Equipment has flameproof gaps (max 0.006" (150 um) propane/ethylene, 0.004" (100 um) acetylene/hydrogen)
2) Pressurized (EX p): Equipment is pressurized to a positive pressure relative to the surrounding atmosphere with air or an inert gas, thus the surrounding ignitable atmosphere cannot come in contact with energized parts of the apparatus. The overpressure is monitored, maintained and controlled.
Strictly according to IEC standard, Flameproof (EX d) cannot be used for decanter centrifuge VFD panel. As the transducer will continually generator heat during working, flameproof is sealed and isolated with environment, it is not good at cooling. It is not stable under higher temperature, the heat cannot cool down fast, so the panel may keep incessant stop.
China use the same EX standard as IEC. But most Chinese company still make flameproof for VFD panel. For our company, we only use flameproof for fixed speed panel.
Advantages of positive pressured control panel: the inside pressure of the panel is higher than outside environment. In this case, the possible explosion gas cannot enter into the panel.
Pressurized panel with air-condition (AC) is a bit bigger in size, but it can cool the panel more easy and for a large temperature scope than vortex tube.
Safety protection: GN VFD panel for decanter centrifuge use positive pressure for explosion-proof, if the air pressure lower than necessary or higher than the allowable, the VFD panel will stop automatically for safety reason.
Important notice:
1) Air should be continually introducing into the panel during running, to keep the higher pressure. The function of the positive pressure is for explosion-proof. Most famous centrifuge brand, they make pressured VFD control panel for Explosion-proof.
2) The air introducing into the VFD panel should come from safety area without possible existing of explosion gas.