Nearly
all the modern generating power plants are located far from the actual
electricity load centres. Transmission of generated power to major load centres
and their further distribution is carried out through transmission and
distribution lines. The losses occurring in the transfer of power from the
generator to the end consumer is known as Transmission and Distribution
(T&D) losses.
Transmission
and distribution network comprises of overhead lines, cables, transformers,
switchgears and other equipments to facilitate the transfer of electricity. The
efficiency of these networks is improved by reducing the T & D losses.
In India electricity is usually generated at a voltage ranging from 11 kV to 25 kV and is stepped up to a voltage of 400 kV or 765 kV (EHV range) for their transmission. Of course bipolar HVDC lines of voltages 500 kV and 600 kV are in use. The voltage is stepped up mainly to reduce the I2R losses. At the distribution end it is again brought down to a very low value. Most of the residential, commercial and agricultural consumers are supplied at a low voltage of 230/415 V. Larger commercial and industrial consumers are typically supplied at voltages of 11 kV, 33 kV or greater values.
In India electricity is usually generated at a voltage ranging from 11 kV to 25 kV and is stepped up to a voltage of 400 kV or 765 kV (EHV range) for their transmission. Of course bipolar HVDC lines of voltages 500 kV and 600 kV are in use. The voltage is stepped up mainly to reduce the I2R losses. At the distribution end it is again brought down to a very low value. Most of the residential, commercial and agricultural consumers are supplied at a low voltage of 230/415 V. Larger commercial and industrial consumers are typically supplied at voltages of 11 kV, 33 kV or greater values.
In
the process of supplying electricity to consumers, some power is
dissipated in the transformers while stepping up or down the voltage levels.
Some power, in the form of I2R losses, is lost in the lines and
cables that carry the power. Losses occurring at various stages of power
transformation and loading of transmission system at 132 kV and above are known
as transmission losses, whereas losses at 33 kV and below this voltage are
distribution losses. Normally the transformer losses are 0.5% of the total
losses, for each voltage transformation. The line losses are nearly 2% for transmission
voltage and are 4% and 5% respectively for primary and secondary distribution
system.
Apart
from T & D losses there are commercial losses too. Therefore
the concept of Aggregate Technical and Commercial (AT & C) loss was
introduced. The AT & C loss reflects the technical as well as commercial
losses in the whole network and hence is the true indicator of the system
efficiency.
Causes
of losses
The
technical losses depend largely on:
- system configuration,
- pattern of loading of transmission and distribution lines,
- magnitude and types of loads,
- characteristics of equipments.
Comparison
between networks of different countries is not straight forward and it is
difficult to define an optimum level of losses for a network. The AT & C
losses vary in various Indian states from 20 to 45% because of the difference
in load density, type of network (urban or rural lines), voltage of supply, geographical size of the area etc.
Other factors such as inadequate design, monetary investments and bad
maintenance of the system over the years contribute to higher losses.
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