DSH 709/06 Short circuit and overload protection
http://decisions.iecee.org/icons/ecblank.gif DSH 709/06
Short circuit and overload protection
15.2
61558-1(ed.2)
Standard(s): IEC 61558-1/2005 No. Year
DSH
0709
2008
Category: SAFE
Subclause(s): 15.2
Developed by: ETF5
OSM/LUM
Subject: Short circuit and
overload protection
Key words:
- Transformers
- Steady state conditions
- Short circuit
Decision approved at the
46th CTL Plenary Meeting,
in 2009
Question:
Inherently short-circuit proof transformers shall be tested by short-circuiting the output windings until
steady-state conditions are reached.
In IEC 61558-1 “steady-state condition” is not explained. Referring to other standards the meaning of
“steady-state conditions” or “thermal stability” is that the change of temperature is less than 1°C per hour.
So following questions arise:
1) Is it correct to record the temperatures after one hour when temperatures did not change (more
than 1°C/h)?
2) How shall an inherently short-circuit proof transformer be assessed when the above mentioned
requirements are fulfilled, but it is damaged 6h after reaching the steady state condition in a way
where safety will be impaired (the transformer bursts).
Decision:
1) Yes.
2) The transformer should not be accepted.
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