Quality Assessment of Dielectric Liquids

The Conductivity Meter For Liquids LCM-8716 is an instrument for measuring of the relative permittivity, the volume conductivity and the dissipation factor of liquid insulation. The instrument is developed according to the new IEC 61620 standard by using the alternate square wave method.

This method permits an accurate determination ob above quantities at ambient temperature. The Conductivity Meter For Liquids LCM-8716 is an easy to use instrument composed of a portable measuring device and a compact low loss test cell.

Quality Assessment of Dielectric Liquids
According to Ohm's law, the volume conductivity σ is a scalar quantity, which relates an applied electric field strength to a material with the generated conduction current density through it. For an homogeneous material and particularly for a liquid subjected to a low electric field, the volume conductivity is constant throughout its volume and it depends on the properties of the liquid material itself and on those of the contained ionisable substances (ionic impurities). Therefore a liquid can well be characterised by its volume conductivity.

The alternate square wave method (low voltage low frequency) according to IEC 61620 standard is an adequate method to determine the volume conductivity σ and the relative permittivity εr of insulating liquids at low temperature without disturbing their thermodynamic equilibrium.

For insulating liquids used in electrical power apparatus, the conduction is the sole cause of loss at power frequencies (50/60 HZ), which are low frequencies indeed. Therefore, the dissipation factor tanδ calculated from the measured σ and εr with the alternate square wave method is equal to the value of tanδ measured with the classic bridge method.

The Conductivity Meter For Liquids LCM-8716 works with the low voltage alternate square wave method and satisfies all the recommendations of IEC 61620 standard:
"Insulating liquids
- Determination of the dielectric dissipation factor by measurement of the conductance
  and capacitance
- Test method"
first edition, dated 1998-11.

The Conductivity Meter For Liquids LCM-8716 can be supplemented with a Test Cell Heater LCM-8716-H and diverse Test Cells can be supplied on request.