By Behrouz ABediAn, TufTs universiT y
ML
www.machinerylubrication.com
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March - April 2015
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11
during fueling operations and why regulations exist to shut off the
engine when pumping fuel into a vehicle.
Static electrification of a dielectric liquid is due to the pres-
ence of trace elements in the oil. Examples of substances that can
carry electric charge in a non-conducting liquid include various
oxidized oil components, contaminating agents, metal salts and
other ionized additives. The concentration of any of these
substances at which liquid electrification occurs can be as low as
1 part per billion. Because of this low concentration, it is imprac-
tical to remove these trace elements. If you could remove them
successfully, subsequent handling could reintroduce the elements
through recontamination.
Engine oils in power systems are electrically insulating liquids
with electrical conductivities in the range of less than 1,000 picosie-
mens (pS) in normal ambient conditions. The value will depend on
how pure the oil is and whether it has been altered with additive
surfactants. For most liquids, the product of their viscosity and
electrical conductivity is constant. As the temperature goes down,
the oil's viscosity increases exponentially, and its electrical conduc-
tivity decreases exponentially.
