DSH 709/06 Short circuit and overload protection

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DSH 709/06 3 D4 T: I" d% @6 S) C

Short circuit and overload protection

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61558-1(ed.2)

Standard(s): IEC 61558-1/2005 No. Year
DSH
0709
2008
' [+ g! V6 |, N: ICategory: SAFE
: V( \, n, C3 o, `Subclause(s): 15.2
Developed by: ETF5
  d% ~' f0 [. J* w' }6 cOSM/LUM
Subject: Short circuit and
overload protection
1 `+ o0 E$ ^! I, M. L& R2 DKey words:
6 p$ O  r( d- t4 u- Transformers
- Steady state conditions
- Short circuit
: F% A$ l6 Q3 C& j7 wDecision approved at the
46th CTL Plenary Meeting,
  ]8 U; w4 }9 q+ }8 A7 G, Lin 2009
: @$ I4 f1 W- p* D! lQuestion:
. F+ c2 r. L3 `6 e4 f: |/ XInherently short-circuit proof transformers shall be tested by short-circuiting the output windings until
9 n( i$ D0 N; p* L/ lsteady-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:
  f, L& l7 G* c, h% t( c1) Is it correct to record the temperatures after one hour when temperatures did not change (more
# o4 w4 h  F) j8 J. ?than 1°C/h)?
. a' ~+ [: T* G; u* }! n2) How shall an inherently short-circuit proof transformer be assessed when the above mentioned
% _9 ?/ _# @6 I% p/ ?* n4 d# E  crequirements are fulfilled, but it is damaged 6h after reaching the steady state condition in a way
' q! J' Q2 C' U- |% z6 W* \5 Gwhere safety will be impaired (the transformer bursts).
% U& k6 W" ]7 S: q2 _Decision:
# T3 o" V- f/ i/ G8 X- X1) Yes.
2) The transformer should not be accepted.
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: z" d) Q3 k! P% ~& X% V6 {0 P