DSH 709/06 Short circuit and overload protection

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DSH 709/06 8 E- K/ T( Q. J/ p9 f

Short circuit and overload protection

15.2 - |& h! f3 B, V- l$ X

61558-1(ed.2) ; I/ P8 |) t- B! A) s6 p9 ?

Standard(s): IEC 61558-1/2005 No. Year
* j2 q! Q$ _) v+ l1 z7 pDSH
0709
2008
Category: SAFE
9 Y8 E" N  N+ `5 Z- q3 @; ASubclause(s): 15.2
; |! {/ m9 L+ I: ~! jDeveloped by: ETF5
OSM/LUM
* d' _; S9 Y1 |1 gSubject: Short circuit and
overload protection
; c& s; A7 P, fKey words:
' h" x% e$ R+ l+ w/ n) X$ i) s9 q- Transformers
- Steady state conditions
2 [- o& s5 K) y: A- Short circuit
Decision approved at the
1 M) F3 E/ Y2 o$ v3 H, b46th CTL Plenary Meeting,
in 2009
0 {8 u2 t( N7 v, H  N1 }/ ~7 \Question:
& X+ {) e6 i9 q8 ?& LInherently 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
8 |: l+ a  q& ~$ s7 T“steady-state conditions” or “thermal stability” is that the change of temperature is less than 1°C per hour.
So following questions arise:
$ o+ a* S; C. ]6 k+ J* T8 l8 u; Q1) Is it correct to record the temperatures after one hour when temperatures did not change (more
7 b! T2 s; o* |than 1°C/h)?
2) How shall an inherently short-circuit proof transformer be assessed when the above mentioned
7 i7 A7 O2 m% r5 C. D' ~: `, W' Rrequirements are fulfilled, but it is damaged 6h after reaching the steady state condition in a way
where safety will be impaired (the transformer bursts).
Decision:
1) Yes.
2) The transformer should not be accepted.
. A6 E4 t1 l" A# v- ~* D
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