DSH 709/06 Short circuit and overload protection

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DSH 709/06 ; G# f: w: t* N7 y# T) p% c1 U+ H

Short circuit and overload protection & e. L! C6 I  d# ~# T2 s9 c8 I

15.2 9 Q3 `$ B6 l. @) ~* N, v+ ?

61558-1(ed.2) 3 j7 B, ~; L( }3 r. t

Standard(s): IEC 61558-1/2005 No. Year
, Z9 G& G3 Z" i# l/ y- |DSH
0709
8 L1 l; F4 m) ~! F( X+ s: D6 O6 \2008
# O0 k( z; W/ LCategory: SAFE
Subclause(s): 15.2
/ j- I: A7 d- w4 F" ?8 NDeveloped by: ETF5
OSM/LUM
Subject: Short circuit and
overload protection
( ^6 e) R& M. _3 iKey words:
- Transformers
- Steady state conditions
- Short circuit
Decision approved at the
' V) i( ~7 E" M. l7 j( x46th CTL Plenary Meeting,
in 2009
Question:
+ x( {, \: d( g$ e) M& n+ FInherently short-circuit proof transformers shall be tested by short-circuiting the output windings until
steady-state conditions are reached.
2 k/ w3 m+ E$ G. uIn IEC 61558-1 “steady-state condition” is not explained. Referring to other standards the meaning of
$ H. }: c4 o( ?- P“steady-state conditions” or “thermal stability” is that the change of temperature is less than 1°C per hour.
So following questions arise:
- m* n0 D" \5 C1 e) w+ v1) 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
* g8 z' E8 i' |, P, J% t& Frequirements are fulfilled, but it is damaged 6h after reaching the steady state condition in a way
where safety will be impaired (the transformer bursts).
8 p: p! Y- q' h. u, \* w, u0 L  JDecision:
$ m, g  @8 `( G1) Yes.
, [- ^1 S# ~# g9 ~" s  w2) The transformer should not be accepted.
; \: ]. h; x" V