Power line connection
246
6.
POWER LINE CONNECTION
Isolating transformer or autotransformer
238
DDS
HARDWARE
Ref.1310
6.4 Isolating transformer or autotransformer
When the mains voltage must be isolated or adapted to the levels re-
quired by the DDS system, it may be connected through an isolating
transformer or an auto-transformer. This element will also help reduce the
amount of harmonics on the line although
it will not guarantee the com-
pliance with the CE regulation.
The following figure shows the position where the transformer or
autotransformer must be installed within the whole power line connection
system.
MANDATORY. When having a mains perfectly referred to ground, auto-
transformers may be used to adapt the mains voltage. However, if mains
is not referred to ground, an isolating transformer must be used in order to
avoid possible dangerous voltage surges on any phase with respect to
ground that could damage the equipment.
In this situation, the secondary must have a star configuration with access
to the middle point. This middle point of the secondary must be connected
to ground or the neuter of mains. This consideration is also applicable to
IT type networks.
MANDATORY. On systems with an XPS power supply, the inductance of
the transformer must be very low and negligible against the inductive val-
ue of the choke XPS.
F. H6/2
Position of the autotransformer or isolating transformer.
MAINS
FILTER
A
DDS
DDS
MAINS
FILTER
A
DIFFERENTIAL
BREAKER
DIFFERENTIAL
BREAKER
MAINS
SWITCH
MAINS
CONNECTION
MAINS
SWITCH
MAINS
CONNECTION
POWER
SWITCH
POWER
SWITCH
MANDATORY. When using transformers or autotransformers, the main
contactor
- KM1 must be connected between them and the DDS system,
never on the input line of the transformer or autotransformer.
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