Electronic Engineering Schematics
Insulation Resistance Theory - doc00030
Insulation resistance is a very complex parameter, but it is
very important to study it in the field of electrical &
electronic engineering. The I.R. value, of a specimen changes
with time on continuous application of D.C.voltage, the IR value
changes with change in magnitude of the applied DC voltage and
IR value also varies with Temperature, Humidity and
Resistance Testing - AEMC
When measurement is made, the IR value slightly increases after
each measurement cycle. This is due to residual polarization of
the previous application of voltage due to all the above
factors, IR measurement becomes both difficult and complicated.
The DRT101 overcomes most of the conventional problems and makes
Insulation resistance analysis more scientific & practical.
Megger - MIT200 Insulation Tester
The problem of residual polarization can be overcome by :
- The terminals of the insulation shorted for a few
- The terminals are reversed after each measurement.
The DRT101 shorts the specimen terminals automatically when it
does not apply voltage. But most accurate results are obtained
only on the 1st measurement on a specimen or by giving a gap of
30 mts for depolarization between each measurement.
When a steady DC voltage is applied to an insulation, the
observed behavior is a analogous to that of changing a leaky
capacitance through a series high resistance. The resultant
current comprises of these components.
- A charging current due to the natural capacitance. This is
large in the beginning and becomes negligible in a few
- The absorption current flows in the body of the dielectric
and decays with time. The time may run to many minutes, this
absorption current gives rise to polarization residue
- The actual conduction current through the insulation. This
is constant with time. But can vary with voltage &
- The surface leakage current depends much on Humidity
Insulation may fail due to the following reasons:
Mode of insulation failure :
- Mechanical vibrations may rupture insulation.
- Temperature decreases thermal strength.
- Dust & moisture cause contamination & decay.
- Corrosive material & electrochemical reactions.
- Intrinsic breakdown.
- Thermal effects.
Methods of measuring high resistance and IR :
- High voltage bridge.
- Leakage current measurement method.
- Loss of charge method.
Here is a Graph from a Scientific Journal which shows
relationship between Temperature and Insulation Resistance or
High Resistance of Substances.
Another graph plotting the relationship of Humidity and
Temperature from the same American journal. I will add the name
of the Author and Document when i locate it in my files. Note
that the graphs are from experts. I was focused on creating the
electronics. I did verify some of the parameter and its
High Resistance Materials Tables
20 C OHM -M
Transformer oil 1010 1013
Gasoline 1010 1013
Castor oil 108 1010
Acetone 104 105
Distilled water 103
Glass At High Temperature
200 C OHM
-M Sodium Pyrex 2 * 106
Potassium Pyrex 8 * 109
Lead glass 2 * 1011
Effect Of Contamination On Surface Resistivity
70% RH CONTAMINATED CLEAN
Window glass 2 * 108
quartz 2 * 108
Relation Of Resistivity With RH % And Temp
MATERIAL 70% RH 20
deg C 0% RH 100 deg C
0% RH 20 deg C
1010 - 1012
1012 - 1014
Wood 106 - 107
1010 - 1012
1011 - 1013
Vulcanized fibers fibers
106 - 109
108 - 109
1011 - 1012
MATERIALS OHM -M Polyethylene
1017 Poly propylene 1017
PVC 1018 Polyurethane
1015 Asbestos fiber + phenol
108 Mica + phenol 1012
Glass-fiber + polyester 1012
Glass-fiber + epoxy 1014
Pages 1, 2, 3, 41, 42, 43 of DRT101 Insulation Tester and
Tera Ohm Meter Operating Manual, A product that i used to
make-n-sell. - delabs
Errors may exist due to scanning and ocr
Back to Insulation Tester
20th Mar 2020