ECT192
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Overvoltage<br />
protection<br />
Internal fault<br />
protection<br />
“Single phase”<br />
operation protection<br />
LV fault<br />
protection<br />
Overload<br />
protection<br />
Mixed or<br />
overhead<br />
network?<br />
Dangerous<br />
single phase<br />
operation<br />
Does the<br />
risk exist?<br />
NOTHING<br />
NOTHING<br />
NOTHING<br />
Do we accept<br />
users to be<br />
cut-off?<br />
Should all<br />
risk be<br />
eliminated?<br />
We accept<br />
the risk of<br />
destroying<br />
the transformer<br />
Is there<br />
low voltage<br />
protection?<br />
Possibility<br />
of faults<br />
< 4I n ?<br />
Appraisal of<br />
the cost/risk<br />
compromise<br />
Do we<br />
accept external<br />
effects?<br />
Do we<br />
want to favour<br />
upstream<br />
continuity?<br />
Suitable LV<br />
protection:<br />
max I >><br />
Do we want<br />
to save the<br />
transformer?<br />
Is there<br />
low voltage<br />
protection?<br />
NOTHING<br />
Do we want to<br />
disconnect the<br />
transformer as soon<br />
as possible?<br />
Thermostat,<br />
thermal<br />
imaging<br />
Are there<br />
several<br />
feeders?<br />
Is the risk<br />
of fuses not<br />
breaking<br />
acceptable?<br />
Cast resin<br />
transformer?<br />
Residual<br />
current,<br />
temperature<br />
probes<br />
Residual current,<br />
pressure, gas<br />
release,<br />
thermostat<br />
Thermostat,<br />
thermal imaging,<br />
max I > on LV<br />
protection<br />
Selectivity<br />
between<br />
feeders and<br />
upstream level<br />
Are there<br />
any priority<br />
loads?<br />
Lightning<br />
arrestors<br />
Associated<br />
fuses<br />
Full range<br />
fuses<br />
Fuse switch<br />
combination<br />
Circuit-breaker<br />
+ relay<br />
Load shedding<br />
and selectivity<br />
between<br />
feeders and<br />
upstream level<br />
Fig. 30: logic diagram of situations, criteria and solutions.
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