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
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 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.
- The terminals of the insulation shorted
for a few minutes.
- The terminals are reversed after each
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 seconds.
- 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 effect.
- The actual conduction current through the
insulation. This is constant with time. But can
vary with voltage & temperature.
- The surface leakage current depends much on
Insulation may fail due to the following reasons:
Mode of insulation failure :
- Mechanical vibrations may rupture
- Temperature decreases thermal strength.
- Dust & moisture cause contamination &
- Corrosive material & electrochemical
Methods of measuring high resistance and IR :
- Intrinsic breakdown.
- Thermal effects.
Here is a Graph from a Scientific Journal which
shows relationship between Temperature and
Insulation Resistance or High Resistance of
- High voltage bridge.
- Leakage current measurement method.
- Loss of charge method.
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
| Castor oil
Glass At High Temperature
| 200 C
| Sodium Pyrex
|| 2 * 106
| Potassium Pyrex
|| 8 * 109
| Lead glass
|| 2 * 1011
Effect Of Contamination On Surface Resistivity
| 70% RH
| Window glass
|| 2 * 108
| Fused quartz
|| 2 * 108
Relation Of Resistivity With RH % And Temp
|| 70% RH 20 deg C
|| 0% RH 100 deg C
|| 0% RH 20 deg C
|| 106 - 108
|| 1010 - 1012
|| 106 - 107
|| 1010 - 1012
|| 1011 - 1013
| Vulcanized fibers
|| 106 - 109
|| 108 - 109
|| 1011 - 1012
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. -
|| OHM -M
| Poly propylene
| Asbestos fiber + phenol
| Mica + phenol
| Glass-fiber + polyester
| Glass-fiber + epoxy