INTRODUCTION
Transportation of people, goods and
services today is no longer a problem as technology is fast growing.
Distance is neither a barrier nor a problem. Just as people, goods and
services are easily transported across a distant destination, ELECTRICITY
is no different. Electricity can be transported over a long distance.
But unlike goods, electricity requires a medium through which it is
transported. Often times you will notice that the power transmission cables
hanging on electric poles are loose. You might have thought “why
weren’t the cables fastened tight to the poles?”Let’s find out why the
cables are loose on electric poles but before then let’s take a pip at
some important tips that would help us understand better.
POWER TRANSMISSION
Power
is the rate at which work is done. Work is done when electrical energy
is covers a distance. By that we can say that power is energy delivered
per unit time. Electricity can be transported over a long distance via
cables which serve as a medium of transporting the electricity. Power is
measured in watts. When transmitting power, high-voltage transmission
is preferred so as to save energy. Electric current causes the
dissipation of heat and this heat is really not good as it causes the
electric cables to wear out and cut that is why in order to save the
transmitted power, electric current which causes heat and eventually
wearing out of cables must be transported in a small quantity while the
voltage in large quantity hence the name High-Voltage power
transmission.
CONDUCTION AND LINKAGE
During power transmission, electrical power is licked to our surrounding as the transmission cables
are not insulated. According to Ohm’s law, Resistance R varies directly
with the length of the conductor L, meaning that as the length of the
conductor increases, its resistance increases. Air is not a good
conductor and as such it cannot conduct away the heat dissipated by the
electric cables, which is why the electric cables are engineered in such
a way that it offers little or no resistance to the flow of electric
current by increasing the diameter of the conductor. Resistance R varies
inversely to the area of the conductor – the bigger the diameter of the
conductor, the less the resistance and vice versa.
ELECTRIC CABLES
Electric cables are conductors mostly copper wires
through which electricity is transmitted. The cables however are not
purely copper. In order for the cables to have some mechanical
properties, the conductors are alloyed. The conductivity of the
conductor is not affected by the other element with which it was
combined. The other element gives the copper a mechanical property
without affecting its conductivity.
JOULE’S LAW OF ELECTRICAL HEATING
There is nothing as a pure metal. The
degree of purity of any metal is never 100% pure and as such they have
internal resistance. Energy expended or heat generated when current
flows through the conductor is given by;
P = VIt
P = I2Rt.
P = VIt
P = I2Rt.
Other forms of Joule’s Law
P = I2Rt
P = VIt … (R = V/I)
P = Wt … (P = W = VI)
P = V2t/R …. (I = V/R ) using simple Ohm’s Law
P = I2Rt
P = VIt … (R = V/I)
P = Wt … (P = W = VI)
P = V2t/R …. (I = V/R ) using simple Ohm’s Law
As can be seen from the equation above,
Heat (P) generated by the moving electrons is proportional to R, t,
I^2.When an electric current flows through a conductor, electric current
is being dissipated to the surrounding in form of heat when overcoming
resistance which serve as a barrier to the drifting electrons.
EFFECT OF WEATHER AND TEMPERATURE ON ELECTRIC CABLES
The resistance
of a conductor increases with increase in temperature. This is because,
as the temperature of the conductor increases, the electrons embedded
in the conductor gain more energy and moves randomly thereby colliding
with the other atoms which will later lead to heat as a byproduct. The
heat produced by the conductor when intense can lead to the melting of
the conductor itself. When the weather is hot, the cables tend to be
more loose as the conductor will expand but when cold, the cable will
contract.
TENSION IN CABLES
Tension a force that exist in a string
that is under the action of two forces in opposite direction. Thus a
cable hanging on a pole is under tension and would be under more tension
if the cables are to made tight which would make the cables to cut
easily when little contraction or expansion occurs.
Why Power Transmission Cables & Lines are Loose on Electric Poles & Transmission Towers?
During transmission of electricity, heat
is being dissipated. The heat generated by cables is being minimized
via high voltage transmission. The effect of weather and the internal
temperature of the cable make it necessary to let the cables a little
bit loose.
If the cables were made tight and the
weather gets cold, it would cause the transmitting cables to contract
thereby creating more tension in the cables which might cause it to cut.
So, the cables are loose so that even if contraction should occur,
there won’t be much tension which would lead to the damage of the
cables.
