General Introduction –
Transmission and Distribution
integral solutions
The world’s population is on the increase
and the demand for electrical energy in
the developing and newly industrializing
nations is growing rapidly. Safe, reliable
and environmentally sustainable power
transmission and distribution is therefore
one of the great challenges of our time.
Siemens is making an important contribu-
tion towards solving this task, with future-
oriented technologies for the construction,
modernization and expansion of power
systems at all voltage levels.
The Siemens Power Engineering Guide
Transmission and Distribution gives a short
summary of the activities and products of
the Power Transmission and Distribution
Group.
Transmission and distribution networks are
the link between power generation and the
consumers, whose requirements for elec-
trical energy determine the actual genera-
tion. Industry, trade and commerce as well
as public services (transportation and com-
munication systems including data pro-
cessing), not to mention the private sector
(households), are highly dependent upon
a reliable and adequate energy supply of
high quality at utmost economical condi-
tions. These are the basic conditions for
installation and operation of transmission
and distribution systems.
Transmission
The transmission of electrical energy from
the generating plants, which are located
under the major constraints of primary en-
ergy supply, cooling facilities and environ-
mental impact, to the load centers, whose
locations are dictated by high-density urban
or industrial areas, requires a correspond-
ingly extensive transmission system.
These mostly interconnected systems, e.g.
up to 550 kV, balance the daily and season-
al differences between local available gen-
erating capacity and load requirements and
transport the energy to the individual re-
gions of demand. For long-distances and/or
high-capacity transmission, extra-high-volt-
age levels up to 800 kV or DC transmission
systems are in use.
In interconnected transmission systems,
more and more substations for the sub-
transmission systems with high-voltage
levels up to 145 kV are needed as close
as possible to the densely populated areas,
feeding the regional supply of urban or in-
dustrial areas. This calls for space-saving
enclosed substations and the application
of EHV and/or HV cable systems.
Distribution
In order to feed local medium-voltage
distribution systems of urban, industrial or
rural distribution areas, HV/MV main sub-
stations are connected to the subtransmis-
sion systems. Main substations have to
be located next to the MV load center for
economical reasons. Thus, the subtrans-
mission systems of voltage levels up to
145 kV have to penetrate even further into
the populated load centers.
The far-reaching power distribution sys-
tem in the load center areas is tailored ex-
clusively to the needs of users with large
numbers of appliances, lamps, motor
drives, heating, chemical processes, etc.
Most of these are connected to the low-
voltage level.
The structure of the low-voltage distri-
bution system is determined by load and
reliability requirements of the consumers,
as well as by nature and dimensions of
the area to be served. Different consumer
characteristics in public, industrial and
commercial supply will need different
LV network configurations and adequate
switchgear and transformer layout. Espe-
cially for industrial supply systems with
their high number of motors and high
costs for supply interruptions, LV switch-
gear design is of great importance for
flexible and reliable operation.
Independent from individual supply charac-
teristics in order to avoid uneconomical
high losses, however, the substations with
the MV/LV transformers should be located
as close as possible to the LV load centers
and should therefore be of compact de-
sign.
The superposed medium-voltage system
has to be configured to the needs of these
substations and the available sources
(main substation, generation) and leads
again to different solutions for urban or
rural public supply, industry and large build-
ing centers.
Despite the individual layout of networks,
common philosophy should be an utmost
simple and clear network design to obtain
■ flexible system operation
■ clear protection coordination
■ short fault clearing time and
■ efficient system automation.
The wide range of power requirements
for individual consumers from a few kW to
some MW, together with the high number
of similar network elements, are the main
characteristics of the distribution system
and the reason for the comparatively high
specific costs. Therefore, utmost standard-
ization of equipment and use of mainte-
nancefree components are of decisive im-
portance for economical system layout.
Siemens components and systems cater
to these requirements based on worldwide
experience in transmission and distribution
networks.
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