DSH 709/06 Short circuit and overload protection

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DSH 709/06 / v+ a  e, o: \, i& X0 }% ]

Short circuit and overload protection * i1 E3 U" L; |. k2 V. J, U- `) u

15.2 # ?' E# M  O) p

61558-1(ed.2)

' |) H* `# D! u9 s  WStandard(s): IEC 61558-1/2005 No. Year
DSH
0709
$ t# u4 k8 e- m: z7 ]# U2008
Category: SAFE
% o3 D7 i8 f) I: Y/ N. M, L% j+ rSubclause(s): 15.2
Developed by: ETF5
OSM/LUM
Subject: Short circuit and
overload protection
5 S4 C# F5 H7 \5 GKey words:
7 ]; C4 S8 d1 N2 _( o4 Q- Transformers
- Steady state conditions
! G$ b* ]4 Y/ K' F- Short circuit
Decision approved at the
46th CTL Plenary Meeting,
4 |# w$ r5 e* Q8 G9 K: m; Cin 2009
4 T0 x  H* ]1 KQuestion:
7 c7 Z# c2 `: J$ I  D0 aInherently short-circuit proof transformers shall be tested by short-circuiting the output windings until
/ G) Z0 ~+ i- d9 Osteady-state conditions are reached.
In IEC 61558-1 “steady-state condition” is not explained. Referring to other standards the meaning of
! r3 O/ E# J' M% `  |" W' |6 \/ u“steady-state conditions” or “thermal stability” is that the change of temperature is less than 1°C per hour.
! C7 l7 Y9 u# A3 a: G4 ?So following questions arise:
' @5 r3 M. W6 x1) 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
" [! h, g% h, b8 X* M* K1 Mrequirements are fulfilled, but it is damaged 6h after reaching the steady state condition in a way
where safety will be impaired (the transformer bursts).
% F+ Q5 C7 X; IDecision:
1) Yes.
- W. W6 s* @7 r2) The transformer should not be accepted.