This document discusses cables and their components. It begins by introducing conductors, the different types of conductors including materials like copper, aluminum and their properties. It then discusses different types of wires, how they are used in appliances and their characteristics. The document outlines the different types of cables, their electrical properties like capacitance and stress. It describes grading of cables to reduce electrical stress through methods like capacitance grading and difficulties with capacitance grading.

1. CABLES

2.  INTRODUCTION
 CONDUCTORS
 TYPES OF CONDUCTORS
 WIRES
 TYPES OF WIRES
 WIRING APPLIANCES
 CABLES
 ELECTRICAL CHARACTERSTICS OF CABLES
 ELECTRICAL STRESS
 GRADING OF CABLES
 CAPACITANCE GRADING
 DIFFICULTIES OF CAPACITANCE GRADING

3. CONDUCTORS
-
-
-
-
High Resistance
-
-
-
-
-
-
- -
-
-
-
-
-
Low Resistance
A conductor has many free electrons so is good at transferring
electrical current
Good Conductor Bad Conductor
Conductance is the opposite of resistance
It is measured in ‘Mho’s (ohm backwards) ℧

4. DIFFERENT TYPES OF
CONDUCTORS
Material Used
Copper
High conductivity
Easily soldered
Heavier & more
expensive than
aluminum
Copper used in house
wiring
1mm2, 1.5mm2
4mm2 , 6mm2
Aluminum
60%
conductivity
of copper
Cheap &
lighter than
copper
Lowest
conductivity
Heavier than
aluminum
Galvanized Iron (GI)
Used in
overhead
lines

5. DIFFERENT TYPES OF
CONDUCTORS
Respective of their property
Good Conductors Bad Conductors
Medium
resistance
Used for
converting
electrical
energy into
heat, light &
sound
PVC, glass
High
resistance
Non Conductors
Carry current
Low resistance
Copper & Aluminum
Tungsten & Nichrome
Insulators
Wires & cables
use conductors
& non
conductors to
their advantage

6. DIFFERENT TYPES OF
CONDUCTORS
Physical Appearance
Solid Conductor
Used in cables.
e.g. copper,
aluminum, steel
Stranded Conductor
Flexible
1.13 to 3.73 mm diameter
1, 7, 19, 37 stands
Multi stranded Conductor
0.2 or 0.3 mm diameter
14, 22, 24,84 strands
Flexible Conductor
14, 23, 40 strands
<0.2 mm diameter

7. WIRES & CABLES
Wires
Domestic & small industry wiring
In appliances
Cables
Small & big industries
Distribution Lines
Transmission lines
The size & type of wire/cable must suit the power rating required for
their use. The higher the power the thicker the wire/cable
Wires & Cables are purpose built conductors

8. TYPES OF WIRES
Vulcanized India Rubber (VIR)
suitable for: low &
medium voltage supply
only
tinned copper/ aluminum
Cotton tape & cotton
braiding
Bitumen
Vulcanized India Rubber
(VIR)
To protect against corrosion
from the VIR
Old type: not
readily available
to purchase

9. TYPES OF WIRE
Cabe Tyre Sheath wire (CTS)
tinned copper
Rubber/plastic
Thicker
Rubber/plastic
Don’t absorb moisture
Available in 250/440V only
Old type: not
readily available
to purchase

10. TYPES OF WIRE
PVC Wire
copper/ aluminum
Polyvinyl chloride (PVC)
Widely used
Long life
Durable against
water, heat, oil,
UV light
Available in 600,
660, 1100
Voltage

11. WIRING APPLIANCES
Earth
Takes current to ground if
appliance has fault
Live
Provides current to
appliance
Neutral
Returns current
to power source
What do each of these
wires do?

12. CABLES
Larger sized conductors
Type of insulation
Types of cable are sorted by:
Cotton covered
Silk coated
Asbestos covered
Rubber coated
PVC coated
Type of conducting material
Their shape
Unarmored
Armored
Voltage Grade
Low
High
Copper
Aluminum
Mechanical protection
Flat
Round

13. ELECTRICAL CHARACTERISTICS OF
CABLES
• Electric Stress in Single-Core Cables
• Capacitance of Single Core Cables
• Charging Current
• Insulation Resistance of Single- Core Cables
• Dielectric Power Factor & Dielectric Losses
• Heating of Cables: Core loss ; Dielectric loss
and
inter-sheath loss

14. ELECTRICAL CHARACTERISTICS OF
CABLES

15. Electric Stress in Single-Core Cables
D= q/(2πx)
E = D/ε = q/(2πεx)
q: Charge on conductor surface (C/m)
D: Electric flux density at a radius x (C/m2)
E: Electric field (potential gradient), or electric
stress, or dielectric stress.
ε: Permittivity (ε= ε0. εr)
εr: relative permittivity or dielectric constant.

16. r
R
x
V
x
q
E
r
R
q
dx
E
V
R
r
l
n
.
.
2
l
n
2
.



 


r: conductor radius.
R: Outside radius of insulation or inside radius of
sheath.
V: potential difference between conductor and
sheath (Operating voltage of cable).
Dielectric Strength: Maximum voltage that dielectric
can withstand before it breakdown.
Average Stress: Is the amount of voltage across the
insulation material divided by the thickness of the
insulator

17. Emax = E at x = r
= V/(r.lnR/r)
Emin = E at x = R
= V/(R.lnR/r)
For a given V and R, there is a conductor radius that
gives the minimum stress at the conductor surface. In
order to get the smallest value of Emax:
dEmax/dr =0.0
ln(R/r)=1 R/r=e=2.718
Insulation thickness is: R-r = 1.718 r
Emax = V/r (as: ln(R/r)=1)
Where r is the optimum conductor radius that satisfies
(R/r=2.718

18. GRADING OF CABLES
 Grading of cables means the distribution of
dielectric stress such that the difference
between the maximum and minimum electric
stress is reduced.
 Therefore, the cable of the same size could be
operated at higher voltages or for the same
operating voltage,
a cable of relatively small size could be used.
TYPES OF GRADING
 CAPACITANCE GRADING
 INTERSHEATH GRADING

19. CAPACITANCE GRADING
This method involves the use of two or more
layers of dielectrics having different
permittivities, those with higher permittivity
being near the conductor.
Ex =q/(2 πεo.εr .x)
The permittivity can be varied with radius x
such that (ideal case):
εr = k/x
Then Ex =q/(2 πεo. k)
Ex is constant throughout the thickness of
insulation.

20. In the figure shown
At x=r Emax1 =q/(2 πεo. ε1r)
At x=r1 Emax2 =q/(2 πεo. ε2r1)
At x=r2 Emax3 =q/(2
πεo. ε3r2)
If all the three dielectrics are
operated at the same
maximum electric stress
(Emax1=Emax2=Emax3=Emax) ,
then:
(1/ ε1r) = (1/ ε2r1) = (1/ ε3r2)
ε1r = ε2r1 = ε3r2, get r1 , r2

21. The operating voltage V is:














   
2
2
1
2
1
1
max
2
3
1
2
2
1
1
ln
ln
ln
ln
2
ln
2
ln
2
.
.
.
1 2
1 2
r
R
r
r
r
r
r
r
r
E
V
r
R
q
r
r
q
r
r
q
dx
E
dx
E
dx
E
V
o
o
o
r
r
r
r
R
r
x
x
x







22. DIFFICULTIES OF GRADING
Capacitance grading :
1- non-availability of materials with widely varying
permittivities.
2- The permittivities of materials will be change with time, so
the electric field distribution may change and lead to
insulation breakdown.
2
3
1
2
2
1
1
ln
1
ln
1
ln
1
2
C
r
R
r
r
r
r
V
q
o








CABLE
CAPACITANCE