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Conductivity Meter for Liquids LCM-8716

A QUICK INTRODUCTION HOW TO PERFORM EASY AND ACCURATE MEASUREMENTS OF CONDUCTIVITY AND TAN ON INSULATING LIQUIDS

ALFF ENGINEERING www.alff-engineering.ch SwitzerlandALFF ENGINEERING www.alff-engineering.ch Switzerland

The equipment•THE ELECTRONIC MEASURING DEVICE•THE CELL•TWO CABLES•A THERMOMETER


Determination of Permittivity r,Conductivity

and Dissipation factor, tan = /2for

According to IEC 61620 standard*)

*) Insulating liquids – Determination of the dielectric factor by measurement of the conductance and capacitance – Test

method Measurement based on so called „low

amplitude, low frequency“ method, applying an alternate square wave voltage

Amplitude of applied voltage: 30 VFrequency of applied voltage: 0.5 Hz


Applied voltage u(t)

Generated current i(t)

Time

Time

IC=C V/TF

IR=V/R=GV

+V

-V

Capacitance: C=ICTF/V=or Co

Conductance: G=IR/V=(/o) Co

IR: resistive current

IC: capacitive current

TF

Principle of operation applying an alternate square wave voltage


Determination of Dissipation Factor, tan

According to IEC 61620 StandardMeasured quantities:

Resistive Current: IR and Capacitive Current: IC

Derived quantities:Conductance: G=IR/V and Capacitance: C=ICTF/V

Derived and displayed quantities:Conductivity: =oG/Co and Relative Permittivity: r=C/oCo

where, Co: vacuum capacitance of measuring cello: permittivity of vacuum equal to 8.854110-12 As/Vm

Derived quantity:Dissipation Factor, tan=G/2fC=/2for

where, f: main frequency i.e. 50 Hz or 60 Hz


Conformity and compatibility of standards

The LCM-8716 is developed according to IEC 61620 Standard*) and works with so called “low amplitude, low frequency, alternate square wave method”.

The classic measurement of dissipation factor with an AC voltage is based on IEC 60247 Standard**).

The IEC 61620 Standard is a complement to the IEC 60247 one.

The measured dissipation factors according both standards are identical.

*) Insulating liquids – Determination of the dielectric factor by measurement of the conductance and capacitance – Test method

**) Insulating liquids – measurement of relative permittivity, dielectric dissipation factor (tan) and d.c. resistivity


Characterisation of electrical insulating liquids with conductivity, permittivity and

dissipation factor

IEC 60296 Standard: Fluids for electrotechnical applications – Unused mineral insulating oils for transformers and switchgear

IEC 60422 Standard: Mineral insulating oils in eletrical equipment – Supervision and maintenance guidance

IEC 61099 Standard: Specifications for unused synthetic organic esters for electrical purposes

These quantities are very sensitive to the presence of soluble polar contaminants and aging products. For the recommended limits see the following standards:


Advantages of the „low amplitude, low frequency“ method in comparison

to the classic method with AC excitation voltage:

Accurate measurement of conductivity (respectively dissipation) factor

Simple design of test cell, low excitation voltage of only 30 V

No influence onto the properties of the liquid proprieties during the measurement (from charge injection into the liquid tested from measuring electrodes).

Comparatively cheap price of cell and measurement instrumentation.

Portable, low weight, no mains required, easy to clean


Test cells Simple design without guarding electrodes Easy to clean Low ratio “electrode surface”/ “liquid volume” minimising the

contamination effects from the surface in contact with the liquid.

Comparatively cheap cell price

Standard cell (160 ml) disassembled Flow cell


HeaterThe heater with PID controller permits accurate measurements in function of temperature from ambient temperature to 90°C (optionally 120°C)

Heater only Heater with cell in receptacle


Evaluation software “LCM-8716 calculator”Generation of reportsInput quantities equal to measured quantitiesComputed quantitiese.g. tan in function of temperature (extrapolation)

Characterisation of temperature dependency from measurement of liquid tested at two different temperatures

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