DSH 709/06 Short circuit and overload protection

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DSH 709/06 ! O/ t# {9 P# c% c# r, o. g$ S

Short circuit and overload protection

15.2 * H' c$ [# [, [/ h

61558-1(ed.2)

# d2 X7 K- t; D* h& P6 ]6 a. iStandard(s): IEC 61558-1/2005 No. Year
& L) u$ r7 S) l+ eDSH
' |2 a2 C& O2 ~- A; L0 @( G0709
2008
Category: SAFE
# X4 R8 ^9 B1 d% b7 G$ z; i( l) V' eSubclause(s): 15.2
Developed by: ETF5
OSM/LUM
+ @& k" B; C. _- N- T% J( ISubject: Short circuit and
overload protection
0 V0 t; y3 s% F8 N3 P% @- OKey words:
- Transformers
- Steady state conditions
- Short circuit
Decision approved at the
  l6 c- o1 e- ]/ d$ s; L! n46th CTL Plenary Meeting,
in 2009
, E# R; w: r- d6 p: hQuestion:
4 ?. m& h& W( jInherently 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.
' ^5 S; k# K; N9 E; t7 H+ USo following questions arise:
7 s: u1 i' Z4 \! s9 y1) Is it correct to record the temperatures after one hour when temperatures did not change (more
0 w3 I% J/ a; O* E1 ]than 1°C/h)?
4 I1 \- O4 U' k7 }- U2) How shall an inherently short-circuit proof transformer be assessed when the above mentioned
( E8 ]0 r- P' l/ X+ T9 Wrequirements are fulfilled, but it is damaged 6h after reaching the steady state condition in a way
8 i& P5 ?; k  H$ e% uwhere safety will be impaired (the transformer bursts).
% A9 \/ a1 K7 |: N1 X% jDecision:
1) Yes.
2) The transformer should not be accepted.

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