DSH 709/06 Short circuit and overload protection

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DSH 709/06 ! X' H# K, ?# V2 k + K* F' p. {6 R8 Y9 c0 D

Short circuit and overload protection . f) {0 C2 I- D8 _

15.2

61558-1(ed.2)

3 M) G7 ], B' {/ l* ~  ~/ WStandard(s): IEC 61558-1/2005 No. Year
8 R  N3 g5 u  p  c4 ^DSH
0709
& j% D; ?/ W# r2 A2008
# w; a  }3 d9 dCategory: SAFE
Subclause(s): 15.2
* k; R+ h. X+ C* c% f) [Developed by: ETF5
( ?- i8 E' u& H! Q- F7 p! Z! rOSM/LUM
Subject: Short circuit and
* M- N1 t9 H$ b7 C& J2 Loverload protection
Key words:
- Transformers
. v' }) c0 ?7 e( r- Steady state conditions
# h* Q. {) ~( I$ g/ z- x9 g6 U- Short circuit
3 u4 @6 Y: u2 h; L2 z1 KDecision approved at the
46th CTL Plenary Meeting,
/ L6 Y9 A4 C. Y, D- D4 ?in 2009
) b# J4 |0 e$ X: x1 ]0 wQuestion:
/ V" {* I, p7 d2 l/ }Inherently short-circuit proof transformers shall be tested by short-circuiting the output windings until
1 o, @  y" t" I  ssteady-state conditions are reached.
/ r5 D/ C' h+ j& f, D2 W3 `4 uIn IEC 61558-1 “steady-state condition” is not explained. Referring to other standards the meaning of
“steady-state conditions” or “thermal stability” is that the change of temperature is less than 1°C per hour.
9 H5 l+ q% U+ x, \9 l/ ^: sSo following questions arise:
1) Is it correct to record the temperatures after one hour when temperatures did not change (more
- ?1 H# N  x" K3 Q& kthan 1°C/h)?
/ Q: o0 B1 M- J$ a2 U2) 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
0 A3 b/ J" H* |- L  k, f1 U( _( twhere safety will be impaired (the transformer bursts).
/ G/ Z* r8 G$ ~( z5 P$ WDecision:
1) Yes.
& ]( M# ~8 B2 E8 K2) The transformer should not be accepted.