geostationary telecommunications satellites electronic telephone set ...

150
Fig. 10
Apart from a highly stable voltage reference
and regulation amplifier, the central unit
for master voltage control contains digital
voltmeters for precision reading of the
distribution voltages of all connected plants
and the voltage differences in relation to each
other and to the reference voltage
additional central equipment for master
voltage control. This central equipment
continuously measures the difference
between the distribution voltage
of each section and a special,
highly stable reference voltage. If a
difference is detected, a correction
signal is sent to the section in question.
This correction signal affects the regulation
level of the units in the section
in such a way that the deviation is eliminated.
A fault occurring in the central unit or
in the connectors will not have any
serious consequences since there is
an internal limitation of the regulation
range, whereby the correction signal
is only able to influence the regulation
level over a small voltage interval
(± 1 V approx.).
Comparison between sectionalized
and unsectionalized systems
It can be seen from table 1 that sectionalizing
reduces the cable costs for
the exchange in question by just over
50 %, or about 5 % of the total cost of
the whole power supply plant. However,
the cost of the equipment for
master voltage control must be added.
This cost is calculated to be in
the region of a half per cent, so that
the gain with sectionalizing can be expected
to be just over 4 % for this exchange.
For a telecommunication plant distributed
over a wide area the cable costs
increase considerably for an unsectionalized
plant, whereas with a well
planned sectionalizing these costs can
be held almost constant.
Sectionalizing gives great advantages
The most important advantages to be
gained by using sectionalized power
supply for large telecommunication
plants are given in the following summary:
1. Sectionalized power equipment
can be placed nearer the load
centres. The length of the distribution
cables is reduced and also
their cross-sectional area for a
given permissible voltage drop.
2. The reliability increases, since any
operational disturbances in a sectionalized
power plant will affect
only a part of the telecommunication
plant. This applies, for example,
to transients in connection
with temporary short circuits in the
d.c. distribution.
3. Busbars can be dimensioned for
less current. The short-circuit
power is reduced, which lowers the
mechanical strength requirements
for busbars etc.
4. The available space can be utilized
better when making extensions. It
is no longer necessary to pay so
much attention to the distance to
the older power plant.
Summary
The conditions that must be laid down
for a power supply system for modern
telecommunication plants can be summarized
as follows:
It must be so technically advanced
that it satisfies with high reliability
all the technical requirements that
are made, and are likely to be made
in the future, by modern telecommunication
plants.
_ The system must have good modularity
in order to facilitate sectiona-
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