Any unintended ignition source in a hazardous industrial environment – even from a failing bearing – can trigger a fire or explosion. The possibility of sparking or flame is why motors and motor controls operating in an atmosphere subject to explosive gases or vapors, combustible dusts, flammable liquids, or ignitable fibers must be fully enclosed.
Controlling motor functions in hazardous environments using variable frequency drives (VFDs) requires solving the problem of electromagnetic interference (EMI) conductive currents caused by the VFDs. Traditional solutions have inherent risks and complexities, but nanocrystalline inductive absorbers provide a safe and effective alternative.
Long-standing solutions come at a cost
Bearing failures from fluting caused by high-speed switching of the VFDs insulated gate bipolar transistor (IGBT) have been wreaking havoc in the motor world since their inception. Hazardous-duty applications are no exception. The new silicon carbide (SiC) and gallium nitride (GaN) switches pose an even greater challenge.
Since the traditionally used shaft grounding devices cannot be used externally in hazardous-duty environments, the most common solution has been to install a shaft grounding device internal to the explosion-proof (XP) motor. This is typically done at the time the motor is manufactured because aftermarket installation requires costly recertification to maintain the motor’s UL rating. Moreover, few motor repair shops have UL approval to rework XP motors and to re-nameplate and re-certify them as explosion proof.
Even if installed at factory build, shaft grounding devices are not cost-effective. An insulated/hybrid bearing is required in 100 hp motors and above, meaning all parts are wearable and will require maintenance and eventual replacement. Technicians must keep the contact point clean and make sure the brush always maintains contact with the shaft in order to ensure continued effectiveness in the hazardous application. This is not possible with internally mounted applications.
Nanocrystalline common mode chokes are the better alternative
The use of nanocrystalline chokes in hazardous-duty applications solves this long-standing industry problem. Common mode chokes are inductors that “choke” the high-frequency currents (in the kilohertz to megahertz range) generated by the high-speed switching of the VFD. Installing this solution at the source of the problem not only prevents bearing failures due to fluting, but it also reduces other electronic interferences to sensitive monitoring equipment.
For more than 25 years, nanocrystalline inductive absorbers have been solving the problem of EMI caused by VFD operation, worldwide. They are increasingly used in hazardous locations, such as petrochemical plants, paper and plastic plants, pharmaceutical plants, oil fields, oil rigs, grain mills, and wastewater treatment plants.
