Protection Engineering Basics and Schemes Protection Engineering | Page 57

resistance in the conduction path of insulator. This is our
main aim. Now question is that why we need it,
sometimes due to moisture or rain, the resistance of
outer surface reduces and can affect the Insulation
resistance of insulator which is under test and give us
wrong reading and on basis of which we will replace our
insulator, which is economically wrong.
Let suppose
As we discussed earlier, outer surface of insulator is
parallel path to the conduction path of insulator.
Insulator
conduction path
resistance=R=2
Mega ohms
Surface
Resistance=R0=0.1
mega ohms
When we apply IR tester without guard, our reading will
be
0.1
=2∗
2 + 0.1
pg. 57