High Voltage DC Power vs AC Power Transmission
High voltage DC power
transmission is being increasingly used in place of high voltage AC power
transmission, particularly for seabed cables and long lines. This increased use
is because of economic and technical benefits specific to DC power transmission.
Introduction
High Voltage DC technology is
an effective and technical solution for the transmission of power over very
long distances. This system is an economical solution to connect grids of
different frequencies or asynchronous grids, too. This technology has some
better qualities compared to AC power transmission and is the only alternative
to high voltage AC transmission.
Although the AC power
transmission technology performs generation and distribution of energy
significantly well, some jobs cannot be performed with high efficiency and low
cost. The DC technology is comparatively beneficial in various fields such as
power transmission over long distances, power transmission between asynchronous
grids, power transmission through cables, and carrying additional power without
increasing the short circuit ratio.
Economic Benefits of High Voltage DC Technology
The total cost of
stabilization of power transmission for very long distance is divided into five
parts. These parts are tower cost, land cost, terminal cost, transmission line
cost, and capitalized cost.
The DC power transmission
system reduces the cost of various parts. The reductions in the cost of power
transmission due to this system are as follows.
Actually, the economic
benefits are mainly dependent on the size of the tower. The size of tower
required for this system is only 30% as great compared to AC power transmission.
Due to the requirement of
smaller size towers, this system requires 50% less land compared to the AC
power transmission. The smaller land requirement enhances its economical
benefits.
The transmission line cost
required for this system is 33% less than the cost required for the AC
transmission system. This is because the DC transmission system requires a
shorter break-even-distance.
Technical Benefits of High Voltage DC Technology
The main technical feature of
the DC transmission systems is high controllability when compared to AC power
transmission. The other features of the system are as follows.
Benefit in load flow
In the DC transmission system
the load flow is totally controlled by the operators present on both sides.
However, in the AC transmission system, the load flow is uncontrolled and
depends on the actual network conditions.
Benefit in peak supply
DC transmission systems have
inherent overload capability; rather they work actively for the peak load. On
the other hand, the overload capability the AC power system is very low and not
controlled by any means.
AC network connection
stabilization
The AC network connection
stabilization at the ends of the power grid is comparatively easier and more
accurate in the DC power transmission system.
Current Applications of High Voltage DC Technology
The DC transmission system has
various applications, but here are described the three most important
applications of this system.
Submarine cable
connections
The DC transmission system is
best for cable transmission because of its symmetrical monopole configuration.
Different cable designs are used worldwide based on this DC transmission. This
system is used in such areas where submarine cables are required to connect to
the main grid such as for energy platforms, offshore wind farms, island
connections, and urban in-feeds.
Back-to-back
transmission
The DC transmission system is
very beneficial for back-to-back transmission in many aspects such as it
doesnt increase the short circuit power and restricts the spread of cascading
disturbances.
Overhead line
transmission
The most economical part of a
DC transmission system is to use it in overhead lines. The overhead lines using
this system require narrow transmission corridors, which decreases the cost.
Summary
The high voltage DC power
system also has some other benefits such as an increase in stability of the AC
system and parallel AC lines. Actually, this system provides benefits mainly
for long distances as it minimizes power loss during transmission. This power
system is best for seabed power transmission and was used in the shared 1961
IFA power grid system of
England and France. The AC power transmission system is limited in various
areas, whereas the DC power transmission system has various technical and
economic benefits.