Transcript Conductivity Meter for Liquids LCM-8716 A QUICK INTRODUCTION HOW TO PERFORM EASY AND ACCURATE MEASUREMENTS OF CONDUCTIVITY AND TANd ON INSULATING LIQUIDS ALFFENGINEERING ENGINEERING.

Conductivity Meter for Liquids LCM-8716
A QUICK INTRODUCTION HOW TO PERFORM EASY AND ACCURATE
MEASUREMENTS OF CONDUCTIVITY AND TANd ON INSULATING LIQUIDS
ALFFENGINEERING
ENGINEERING www.alff-engineering.chSWITZERLAND
Switzerland
ALFF
ALFF ENGINEERING www.alff-engineering.ch
www.alff-engineering.ch Switzerland
The equipment
ALFF ENGINEERING
•THE ELECTRONIC MEASURING DEVICE
•THE CELL
•TW O CABLES
•A THERMOMETER
www.alff-engineering.ch
Switzerland
Determination of
Permittivity r,
Conductivity 
and Dissipation factor, tand = /2for
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 V
Frequency of applied voltage: 0.5 Hz
ALFF ENGINEERING
www.alff-engineering.ch
Switzerland
Principle of operation applying an alternate
square wave voltage
Applied voltage u(t)
+V
Time
TF
-V
Generated current i(t)
IC=C V/TF
IR=V/R=GV
IR: resistive current
IC: capacitive current
Time
Conductance: G=IR/V=(/o) Co
Capacitance: C=ICTF/V=or Co
ALFF ENGINEERING
www.alff-engineering.ch
Switzerland
Determination of Dissipation Factor, tand
According to IEC 61620 Standard
Measured quantities:
Resistive Current: IR and Capacitive Current: IC
Derived quantities:
Conductance: G=IR/V and Capacitance: C=ICTF/V
Derived and displayed quantities:
Conductivity: =oG/Co and Relative Permittivity: r=C/oCo
where, Co: vacuum capacitance of measuring cell
o: permittivity of vacuum equal to 8.854110-12 As/Vm
Derived quantity:
Dissipation Factor, tand=G/2fC=/2for
where, f: main frequency i.e. 50 Hz or 60 Hz
ALFF ENGINEERING
www.alff-engineering.ch
Switzerland
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 (tand) and d.c. resistivity
ALFF ENGINEERING
www.alff-engineering.ch
Switzerland
Characterisation of electrical insulating liquids with
conductivity, permittivity and dissipation factor
These quantities are very sensitive to the presence of soluble polar
contaminants and aging products. For the recommended limits see the
following standards:
 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
ALFF ENGINEERING
www.alff-engineering.ch
Switzerland
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
ALFF ENGINEERING
www.alff-engineering.ch
Switzerland
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
ALFF ENGINEERING
www.alff-engineering.ch
Flow cell
Switzerland
Heater
The heater with PID controller permits accurate measurements in function
of temperature from ambient temperature to 90°C (optionally 120°C)
Heater only
ALFF ENGINEERING
Heater with cell in receptacle
www.alff-engineering.ch
Switzerland
Evaluation software “LCM-8716 calculator”
Generation of reports
Input quantities equal to
measured quantities
Computed quantities
e.g. tand in function of
temperature
(extrapolation)
Characterisation of temperature
dependency from measurement of liquid
tested at two different temperatures
ALFF ENGINEERING
www.alff-engineering.ch
Switzerland