DC system :
Advantages
of DC Transmission :
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There are two conductors used
in DC transmission while three conductors required in AC transmission.
There are no Inductance and
Surges (High Voltage waves for very short time) in DC transmission.
Due to absence of inductance,
there are very low voltage drop in DC transmission lines comparing with AC
(if both Load and sending end voltage is same).
A DC System has a less
potential stress over AC system for same Voltage level. Therefore, a DC line
requires less insulation.
In DC System, There is no
interference with communication system.
In DC Line, Corona losses are
very low.
In High Voltage DC
Transmission lines, there are no Dielectric losses.
In DC Transmission system,
there are no difficulties in synchronizing and stability problems.
DC system is more efficient
than AC, therefore, the rate of price of Towers, Poles, Insulators, and
conductor are low so the system is economical.
In DC System, the speed
control range is greater than AC System.
There is low insulation
required in DC system (about 70%).
The price of DC cables is low
(Due to Low insulation)
In DC Supply System, the
Sheath losses in underground cables are low.
DC system is suitable for
High Power Transmission based on High Current transmission.
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Disadvantages
of DC Transmission:
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Due to commutation problem,
Electric power can’t be produce at High (DC) Voltage.
For High Voltage
transmission, we cannot step the level of DC Voltage (As Transformer cannot
work on DC).
There is a limit of DC
Switches and Circuit breakers (and costly too)
Motor generator set is used
for step down the level of DC voltage and the efficiency of Motor-generator
set is low than transformer.
So the system makes complex
and costly.
The level of DC Voltage
cannot be change easily. So we cannot get desire voltage for Electrical and
electronics appliances (such as 5 Volts, 9 Volts 15 Volts, 20 and 22 Volts
etc.) directly from Transmission system.
AC system :
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