DSH 709/06 Short circuit and overload protection

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DSH 709/06 & B- Y  _. ~. @$ `# n

Short circuit and overload protection

15.2

61558-1(ed.2)

  t& k2 s9 j1 yStandard(s): IEC 61558-1/2005 No. Year
# `$ o+ ]/ e3 m4 ~; k5 l: kDSH
! Q1 z3 y3 ^8 F& k4 J* r" {0709
% K9 V/ L2 G7 \' m6 Y+ _) X* m2008
8 _% D$ i" ^2 i3 qCategory: SAFE
Subclause(s): 15.2
2 p. ^  V, E+ P- cDeveloped by: ETF5
OSM/LUM
Subject: Short circuit and
overload protection
, y2 {# `8 y2 ]9 u( bKey words:
7 f4 O/ s) G7 g8 q- Transformers
- Steady state conditions
- Short circuit
# H" m- a8 x( SDecision approved at the
46th CTL Plenary Meeting,
in 2009
Question:
2 b" g! I* Y) h- X( G! j( j, CInherently 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
7 l' }2 d, {7 @“steady-state conditions” or “thermal stability” is that the change of temperature is less than 1°C per hour.
$ U2 o0 |" Z6 \1 k$ f$ Q% PSo following questions arise:
4 u  [8 V" h; L9 c1) Is it correct to record the temperatures after one hour when temperatures did not change (more
7 C+ h$ [2 F3 y  Tthan 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).
5 x0 }2 k/ F+ c1 U! ]6 nDecision:
/ p# _* t1 }2 r8 w0 n1) Yes.
2) The transformer should not be accepted.
" I( @9 T. F/ p) T
3 m+ M/ j  j3 }# c7 j6 \  N0 C7 G
! E. [# S: {/ Q' w  u