The document discusses percent and per unit systems for representing values. It states that percent values require carrying the factor of 100 in computations, while per unit values represent a value as a multiple of a base value to absorb large differences in absolute values. It then discusses different voltage levels for transmission lines - low voltage lines that provide power to buildings and homes, medium voltage lines used in larger cities, high voltage lines that connect main substations to power plants, and extra high voltage lines used for long distance transmission. Finally, it lists some key factors that affect corona loss on transmission lines - atmospheric conditions, conductor size, spacing between conductors, line voltage, frequency, and humidity. Corona is the phenomenon of a glow

1. PERCENT & PER UNIT SYSTEM
1. Percent value is not convenient for use as the factor of 100
has to be carried in computation
2. Percent value = per unit value*100
3. The use of per unit system is to absorb large difference in
absolute values into base relationships.
ONE LINE DIAGRAM OF TRANSMISSION SYSTEM

2. FACTOR OF TRANSMISSION LINE
Voltage level
1 low voltage line
Lv lines provide power to buildings, factories and houses to drive
motors,lamps, heater etc. the range of voltage is 220 volt to 440 volt. The the
lines are insulated conductors usually made up of almunium often extending
from a local pole mounted distribution t/f to the service entrance of the
consumer. The lines may be overhead or underground and t/f behaves like a
miniature substation.
2 Medium voltage lines
The voltage is usually b/w 2.4 and 69. Such medium voltage radial distribution
system are preffered in the larger cities. In radial system the t/l of spreadout
like fig. from or more substation to feed power to various load centre.
3 High voltage lines
Hv lines connect the main substation to generating station the line are
compose of aerial conductor or ug cables operating at voltages below 230 kv
4 Extra high voltage lines
These lines are used when generating stations are far from the centres. We
put these line in separate class b/c of there special electrical properties. Such
lines operate at voltage upto 800 kv and may as long as 1000km
CONDUCTOR TYPES AND SIZE
The imp factor taken into account In selection of conductor for particular line or
conductivity, tensile strength, fatigue strength, corona loss , local condition and
cost. The conductor are usually stranded. Stranded conductor have not only
grater flexibility but also greater mechanical strength.
Types
 ALL ALUMINIUM CONDUCTOR AAC
 (ACSR) ALUMINIUM CONDUCTOR STEEL REINFORCE
 ALL ALUMINIUM ALLOY CONDUCTORS

3.  ACC
LINE REGULATION AND VOLTAGE CONTROL:-
 Line regulation describes the ability of a system to provide
near constant voltage over a wide range
of load conditions. That’s why we consider line or voltage
regulation and voltage control before designing any
transmission line.
Describe the formation of corona and discus the factors which affect corona loss?
CORONA
The phenomenon of violet glow, hissing noise and production of ozone gas in an
overhead transmission line is known as corona.
FORMATION OF CORONA
The name corona has been derived from the glow surrounding the conductors
when he opera ting voltage is sufficiently high. For over head transmission
system the atmospheric air, which dielectric medium, behavior practically like
perfect insulators when the potential difference between the conductors is small,
with the voltage increase, there is corresponding increase in electric field
intensity. When electric field intensity reaches the critical value of 3000000 v/m,
the air in the immediately vicinity of conductors no more remain di electric but it
ozone and become conducting. the electric breakdown is accomplished by the
following phenomenon.
1. Faint glow appears around the conductors which is visible in the dark

4. 2. There is an acoustical noise.
3. There is a tendency in the conductors to vibrate
4. There is loss of power
5. Ozone and oxides of nitrogen
If the voltage gradient is increased further the size the brightness of the luminous envelope goes on
increasing until finally a spark is establish between the conductors because of complete breakdown of
the insulating properties of air between them.
Factors affecting corona
1. ATMOSPHERIC CONDITIONS
Atmospheric condition due weather affect the corona loss due to extent . The corona loss is
fairly large during foul weather . Foul weather reduces the uniformity of electric field and
lowers the corona formation voltage. The increase of corona loss due to rainfall.
2. CONDUCTOR SIZE
The corona effect depends upon the shape and conditions of conductors. The rough and
irregular surface will give rise to more corona b/c unevenness of the surface decrease the value
of breakdown voltage .thus a stranded conductor has irregular surface and hence give rise to
more corona that a solid conductor
3. SPACING BETWEEN THE CONDUCTORS
If the spacing b/w the conductors are made very large as compare to their diameter they are
may not be any corona affect.
4. LINE VOLTAGE
The line voltage greatly affects the corona. If it is low, there is no change in the condition of air
surrounding the conductors and hence no corna is formed. However the line voltage has such
value that electrostatic stresses is developed at the conductor surface make the air around the
conductor conducting, then corona is formed
5. FREQUENCY
The frequency and waveform of the voltage also affects the corona. As the frequency increase
the corona wi8ll increase.
6. HUMIDITY
Humidity also affects corona voltage. An increase of humidity decrease corona starting voltage.