geostationary telecommunications satellites electronic telephone set ...

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Fig. 2
CHRISTER BOIJE AF GENNAS
Power Supply Department
Telefonaktiebolaget LM Ericsson
A comprehensive knowledge of the whole
power supply system is necessary in order to
be able to effect an optimization
called the electronics factor for the exchange,
see fig. 1. As is clear from
what has been said above the electronics
factor for modern telecommunication
systems is appreciably higher
than for older systems.
More stringent requirements on the
quality of the supply voltages
The introduction of SPC systems has
led to an increase of requirements on
voltage accuracy as well as freedom
from transient overvoltages and undervoltages
in the power supply.
Undervoltages which are of such short
duration that they are completely imperceptible
in electromechanical systems
can cause disturbances in SPC
systems through the loss of stored information.
Such short duration transient
voltage deviations occur, for
example, as a result of a short circuit
and the consequent fuse blowing in
the distribution network. In the LM
Ericsson system this disturbance risk
is prevented by feeding the power consuming
units individually, direct from
the central power plant via cables with
suitably chosen resistance.
This individual feeding is a characteristic
of the distribution system that is
usually called high-ohmic distribution,
and which has been standardized by
LM Ericsson for feeding SPC systems.
The method has been described in an
earlier number of this publication.'
Total optimization of power
supply plants
When designing a power supply system
for modern telecommunication
plants the whole system must be taken
into consideration when optimizing,
that is to say the rack converters and
distribution material as well as the central
power plant. For example, minimization
of only the cost of the central
power equipment can often result in
increased costs for other parts of the
plant, and probably does not give the
lowest total cost for the whole power
supply plant.
Thus an optimization process demands
a very good overall knowledge of the
parts included in the power supply
equipment, from the incoming mains
supply to the power consuming units
in the racks of the telecommunication
equipment, fig. 2.
The following optimization parameters
must be considered:
• Equipment performance requirements.
Towards the telecommunication
equipment these are fixed
by detailed specifications. On the
other hand the internal performance
requirements (voltage levels,
tolerances etc.) within the power
supply equipment can be varied.
For example, it should be possible
to compensate a reduced regulation
capability in the central power
units by an increase in the regulation
range of the rack converters.