The transmission line of electric power.

1. welcome

2. This is presented by 
1. K.M.A. Montakin
Id:173-33-567
2. Kazi Robin Mehedi
Id:173-33-550
3. Md. Selim Reza
Id:173-33-563

3. Topic: Transmission Line

4. What is transmission line….?
Transmission lines are sets of wires, called conductors, that
carry electric power from generating plants to the substations that
deliver power to customers. At a generating plant, electrical
power is “stepped up” to several thousand volts by a transformer
and delivered to the transmission line.

5. Elements of a Transmission Line

6. Elements of a Transmission Line
The principal elements of a high-voltage transmission line are :
 Conductors: usually three for a single-circuit line and six for a double-circuit line. The usual material is
aluminium reinforced with steel.
 Step-up and Step-down Transformers: at the sending and receiving ends respectively. The use of
transformers permits power to be transmitted at high efficiency.
 Line insulators: which mechanically support the line conductors and isolate them electrically from the
ground.
 Support: which are generally steel towers and provide support to the conductors.
 Protective devices: such as ground wires, lightning arrestors, circuit breakers, relays etc. They ensure the
satisfactory service of the transmission line.
 Voltage regulating devices: which maintain the voltage at the receiving end within permissible limits.

7. Types of Transmission Line
Short Transmission Line
Medium Transmission Line
Long Transmission Line

8. A short transmission line is classified
as a transmission line with:
 A length less than 80km (50 miles)
 Voltage level less than 69 kV
 Capacitance effect is negligible
 Only resistance and inductance are taken in
calculation capacitance is neglected.
Short Transmission Line
A Short Transmission Line is defined as a transmission line
with an effective length less than 80 km, or with a voltage
less than 69 kV.

9. A medium transmission line is
classified as a transmission line with:
 A length more than 80 km (50 miles)
but less than 250 km (150 miles)
 Operational voltage level is from 69
kV to approx 133 kV
 Capacitance effect is present
 Distributed capacitance form is used
for calculation purpose.
Medium Transmission Line
A transmission line having a length of more than 80 kms
but less than 250 kms is considered as a medium
transmission line. The parameters are distributed
uniformly along the line. For a medium transmission line,
charging current is appreciable and due to the length of
the line the shunt admittance plays a significant role in the
calculation of the effective parameters of the line.

10. The most commonly used methods for the solution of medium transmissions
lines are
( i) End condenser method
( ii) Nominal T method
( iii) Nominal π method.

11. long transmission line
A long transmission line is classified as
a transmission line with:
 A length more than 250 km (150
miles)
 Voltage level is above 133 kV
 Line constants are considered as
distributed over the length of the
line.
 A long transmission line is defined as a transmission
line with an effective length more than 250 km. In
a long transmission line the line constants are
uniformly distributed over the entire length of line.

12. Advantage and Disadvantages -
Transposition of Transmission Lines
Advantages of Transposing Transmission Line:
 When conductors are not transposed at
regular intervals, the inductance and
capacitance of the conductors will not be
equal.
 When conductors such as telephone lines
are run in parallel to transmission lines,
there is a possibility of high voltages induced
in the telephone lines. This can result in
acoustic shock or noise. Transposition
greatly reduces this undesired phenomenon.
 In practice, however, conductors are not
transposed in the transmission lines. The
transposition is done in the switching
stations and the substations.
 Transposition of Conductors refers to the exchanging of position of
conductors of a three phase system along the transmission distance in
such a manner that each conductor occupies the original position of
every other conductor over an equal distance as shown in figure
below.

13. Disadvantages of Transposing Transmission Line:
 There is literally no drawback associated with transposition but care
must be taken while marking the position of R, Y and B phase at Tower
correctly. In correct marking may lead to mismatch in Phase Sequence
at the Switching Station and what expected in the Transmission Line.

14. Thank You