Power transmission


Electrical Power transmission is
one of the major concern in the power
supply system. There are three main
areas of power system. They are power
generation, transmission and distribution.

Transmission is done by

i. Overhead lines
ii. Underground cables

Power generation station

Electricity is produced in power
plants, which goes through different
levels to reach consumers. Generated
power is stepped up and stepped
down by using transformers and it is
transmitted. In Tamil Nadu, power plants are far from consumers who use power. For example, the important places of power plants are located at Kalpakkam, Koodankulam (Nuclear power station), Neyveli (Thermal power station), Bhavani
sagar Dam, Pykara, Kunda Dam (Water power station) and Kamuti (Solar power station) etc, The generated power is distributed to the consumers through the substations.

Various system of power transmission

i. DC system

a) DC two wire
b) DC two wire with mid point earthed
c) DC three wire system

ii. Single phase AC system

a) Single phase two wire
b) Single phase two wire with
midpoint earthed
c) Single phase three wire

iii. Three phase AC system

a) Three phase three wires
b) Three phase four wires

Direct Transmission

let us see the transmission of DC power from the AC power.The single line diagram of high voltage direct current transmission is given in figure. Alternative current is generated and stepped up to high voltage through the sending end transformer.This high voltage alternating current is converted to the direct current by a mercury arc rectifier. The transmission
of electric power is carried out at high DC voltage. At the receiving end, the
DC voltage is converted into alternating current through the help of thyratrons. This alternating current is reduced to the low voltage through the receiving end transformer for distribution.

Advantages of DC transmission

i. Two conductors are sufficient for
distribution of power supply

ii. There is no inductance and capacitance.

iii. No skin effect in DC transmission

iv. The corona loss is lower as compared to AC system.
v. Voltage drop is very low.

Disadvantages of DC transmission

i. It is difficult to produce high voltage
ii. The voltage cannot be increased or
decreased by using a transformer

Alternative transmission

From the power generating stations,
a large amount of AC supply is produced and is transmitted through transmission lines. Above Figure shows the layout of a typical AC
power supply system. The transmission is done caried by 3 phase 3 wire and 3 phase
4 wire systems. Other methods are also used for some special reasons.

Two types of transmission are

i. Primary transmission and
ii. Secondary transmission

Primary transmission

In the primary transmission, the
voltage produced from power plants,
transmitted over the transmission lines to the substations with the help of step up transformer.

Secondary transmission

The voltage transmitted by the
primary transmission is reduced by a step down transformer, and is transmitted to the sub-stations in the city.

Advantages of AC transmission

i. Alternate current can produce voltage (33 KV) at the highest level.
ii. The voltage can be increased or
iii. High voltage transmission reduces
iv. It is easy to maintain sub-stations and less expensive.

Disadvantages of AC transmission

i. The AC line has the capactive and
inductive effect.
ii. Due to skin effect, it requires more
effective conductors.
iii. The construction of AC transmission is complicated.
iv. More copper conductors are required for transmitting AC.

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