Composite insulators

1. COMPOSITE INSULATORS

2. INTRODUCTION

The insulators or dielectric, is a material that resists
the flow of electric current.
An insulating material has atoms with tightly bonded
valence electron
Material like glass, paper, Teflon are very good electric
insulators.

3. WHAT ARE COMPOSITE INSULATORS?

A composite insulator in one made of at least two
insulating parts, namely a core and a housing
equipped with metal fittings. Composite insulators, for
example, can consist either of individual sheds
mounted on the core, with or without an intermediate
sheath, or alternatively, of a housing directly moulded
or cast in one or several pieces on to the core. This kind
of insulator can be used on transmission and
distribution lines, and also the electric railways.

4. HISTORY

The first electrical systems to make use of insulators were telegraph lines;
direct attachment of wires to wooden poles was found to give very poor
results, especially during damp weather. The first glass insulators used in
large quantities had an unthreaded pinhole. These pieces of glass were
positioned on a tapered wooden pin, vertically extending upwards from the
pole's crossarm (commonly only two insulators to a pole and maybe one on
top of the pole itself). Natural contraction and expansion of the wires tied to
these "threadless insulators" resulted in insulators unseating from their pins,
requiring manual reseating. Amongst the first to produce ceramic insulators
were companies in the United Kingdom, with Stiff and Doulton using
stoneware from the mid 1840s, Joseph Bourne (later renamed Denby)
producing them from around 1860 and Bullers from 1868. Utility patent
number 48,906 was granted to Louis A. Cauvet on July 25, 1865 for a
process to produce insulators with a threaded pinhole. To this day, pin-type
insulators still have threaded pinholes. The invention of suspension-type
insulators made high-voltage power transmission possible. Pin-type
insulators were unsatisfactory over about 60,000 volts. A large variety of
telephone, telegraph and power insulators have been made.

5. TYPES OF COMPOSITE INSULATORS

Composite Suspension Long
Rod Insulators
Used on overhead suspension or tension
power transmission lines, and suitable
for the middle and above contamination
areas, particularly in the heavy
contamination areas. There are several
ways of connecting of fitting:ball &
socket,
clevis
&
tongue,
Yclevis. Generally, the voltage level is
from 10 KV to 1000KV.
15kv, 25kv, 35kv ANSI deadend
insulator, 66KV, 110KV, 220KV,
400KV,500KV
silicone
rubber
insulator and etc is normally used.

6. Silicone Rubber Composite Pin/Line Post Insulator: 

.
It is suitable for the rebuild
of city lines. The voltage
levels typically from 6 to 36
KV. 11kv and 33kv pin
composite insulators are
normal types. Its top and
bottom installed are the same
as the corresponding size of
porcelain insulator, so they
can be interchangeable use.

7. Composite/Silicone Rubber Post Insulator:

The composite station post
insulators mainly apply to
transformer substation and
switches
and
other
apparatus. The voltage can
be upto 220KV and now
most
of
the
small
apparatus has chosen
polymer post insulator to
instead of porcelain ones
since they have more
advantages.

8. Composite Cross Arm Insulators 

It has an effective use of a
narrow corridor pressure
transmission
and
applicable to rebuild of
city power net. It can also
reduce the tower height,
saving
manpower,
material and financial
resources. It has a
superior
performance
than porcelain insulator.

9. Electrified Railway Composite Insulators 

Composite
insulator for
railway traction lines is used
in tunnels of electrified
railway
under
severe
conditions.
They
can
effectively prevent pollution
flashover outage and free
from
cleaning
and
maintenance work. It will
hold on not only tension, but
also bending. With a very
small size, they can hardly be
substituted by porcelain or
glass insulators in case if
small tunnel space

10.

FACTORS
CERAMIC
COMPOSITE
Resistance to flashovers in
Polluted atmosphere.
Low
High
Resistance to puncture
Resistance to Cracking and
Erosion in Polluted
atmosphere
Puncturable
Low
Not puncturable
High
Contamination & Pollution
Highly affected
Performance not affected
Hydrophobicity
Non hydrophobic
Unique Hydrophobicity
character.
Self cleaning property
Due to Glaze and inclination
of sheds
Due to Hydrophobicity
recovery characteristic.
Maintenance
Needs maintenance like
cleaning, washing, greasing
No maintenance is required
Weight
More
10% to 35% of Ceramic
Insulator
Resistance to breakage and
Vandalism
Breakable in Vandalism
prone areas
Unbreakable

11. Composite Stay Insulators

It is a new type to instead
of porcelain buy
strain insulators and have
better tensile strength, low
weight and good looking,
the normal type develop
now is 97KN. Normally
used in Africa. only the
end fitting and fiber glass
core and covered with
something special to have
better performance.

12. Outdoor Switch Post Composite Insulators 

This type insulator is
suitable for outdoor used
in AC switchgear and
switch disconnectors with
voltage up to 25 kV and
38.5KV.
Main advatages are low
weight, outstanding
dielectric strength and
extreme mechanical
endurance

13. BENEFITS

Light weight (25-30% less than ceramic insulator)
Silicone rubber sheds provides perfect hydrophobic
performance, Good resistance to aging, tracking and erosion.
Stable behavior at extreme climate conditions.
Long term surface hydrophobicity.
Suitability for polluted environment, salty atmospheres etc.
Resistance to breakage and vandalism, Practically unbreakable.
Superior anti-tracking properties.
High mechnical strength.
Ease of installation (easier handling with lighter equipment and
labor at the job site)
Resistance to Seismic Shock

14. CONCLUSION

The paper discusses selected advantages of composite
insulators and structures for lines with compact requirements.
Beside the recognized properties of Silicone Rubber insulators
in polluted areas, the mechanical performance
offers with the safe failure mode a feature that improves the
line reliability significantly and permits suitable arrangements
for areas with limited right of ways. In respect to the principle
performance, the shown examples for transmission level are
applicable to distribution level as well. The substitution of steel
as reinforcing material by carbon fibres is shown on the
example of an 110kV pole for a line upgrade from 52 kV.