Basic electrotechnical units and theory
83
∴
230
4
57 5
V
A
.5 109
Aluminium 28.0 109
.
R
l
a
ρ
( )
where
ρ the resistivity constant for the material m)
l the length the material (m)
a the cross-sectional area the material (m2
). Calculate the leakage current.
Example 2
The insulation resistance measured between phase conductors 400 supply was found
to 2MΩ. Using the constants for particular material
we can calculate the resistance any length and thickness that material
from the equation.
Table 4.3 Resistivity Values
Material Resistivity m)
Silver 16.
I
V
R
∴
400 V
2 10
200 200 A
6
6
Example 3
When resistor was connected across the terminals unknown d.
The resistivity (symbol the Greek letter ‘rho’) material defined
as the resistance sample unit length and unit cross-section. know the resistance of, say,
1m material, then the resistance will five times the resistance
of 1m.5 109
Brass 75. Calculate the supply voltage.
V R
V
12
A V
Resistivity
The resistance opposition current flow varies for different materials,
each having particular constant value.c.
Definition
The resistivity (symbol the Greek
letter ‘rho’) material defined
as the resistance sample unit
length and unit cross-section. Typical
values are given Table 4. supply, current
of flowed.4 109
Copper 17.3.0 109
Iron 100
