DSH 709/06 Short circuit and overload protection

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DSH 709/06 1 Z# U4 ~5 ]% A3 e! {

Short circuit and overload protection ' y# R* O) p- Y7 E7 b& N+ @0 N

15.2

61558-1(ed.2) % J# A' X3 Q% ~* U/ V# s& S5 u

Standard(s): IEC 61558-1/2005 No. Year
8 V! i! B% f( e. l, a0 s, S7 ODSH
0709
3 v5 C5 [/ A  i" \3 f1 q2008
Category: SAFE
Subclause(s): 15.2
Developed by: ETF5
! h4 {; @0 O7 e% KOSM/LUM
Subject: Short circuit and
overload protection
4 J/ ]/ h: j- `* SKey words:
. Q" l4 ?. ~( e5 Y$ r) x- Transformers
9 q2 o# x1 n: G! @- Steady state conditions
& D6 h4 e  D# v. R' ^- Short circuit
Decision approved at the
46th CTL Plenary Meeting,
in 2009
) v& @- j3 x* kQuestion:
# C( W; p. x& |1 ?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
% ~+ r- N0 ^- F. H. B* _5 ]“steady-state conditions” or “thermal stability” is that the change of temperature is less than 1°C per hour.
So following questions arise:
8 s% V1 _: K1 ~% {: j: N  p9 z1) Is it correct to record the temperatures after one hour when temperatures did not change (more
than 1°C/h)?
& @8 ?- S* z" a. K  Q2) 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
6 n$ t3 w: V- Twhere safety will be impaired (the transformer bursts).
Decision:
1) Yes.
2) The transformer should not be accepted.
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