Mains supply transformers: Short Circuit and Overload tests ' v9 ]/ m% s( ]! G H) N# |
57.9.1: G1 l; e- {2 ?+ H3 [' F5 g
60601-1(ed.2);am1;am2$ W. `- g. `. `! q5 z
$ I% D( W5 b; o( MStandard(s)- (year and edition): ; m% w) A ]/ u% E5 T0 NIEC 60601-1:1988 Ed.2 Am1+Am2 $ F: }% q( b$ BSub clause(s): 57.9.1 0 S: Q7 L, H# ?! ]4 KSheet n°: DSH-401 8 s: l% |" F/ X+ b( c0 aSubject: Mains supply transformers: Short Circuit and Overload tests $ V0 B; c5 Z8 v, e [& t+ _$ p/ x9 ? SKey words: Over-current, protection, overload4 K6 ]7 V9 O6 p) h
Confirmed by CTL at its 39th meeting, in Cologne $ U. |; b' j- gQuestion:9 w q4 G; z6 m- j1 P
Secondary circuit OVER-CURRENT PROTECTION is the first active component on the4 S v$ u5 S+ ^
secondary side of a mains supply transformer. Is the overload test performed before or after the 1 t1 v# |6 w4 k7 \( ^( u! {fuse?) z8 t2 V( @5 P: n+ l
Insufficient transformer winding crossover insulation and secondary circuit CREEPAGE5 p# j" n9 Z! C2 s' M
DISTANCES and AIR CLEARANCES causes transformer winding to short-circuit and exceed: A1 Z; S5 p2 I" p' P
allowable temperatures.4 ]! m) Z# c9 N1 I& J
Decision:. G: L& ?3 Q" |) t1 |
If the possibility of a short-circuit exists before the secondary OVER-CURRENT PROTECTION $ A% m$ i6 s1 U7 X# [) D8 b' i/ w. r+ mdevice (e.g. failure of basic insulation between winding or detachment of the wiring) the short) P* V8 q: N3 S* O+ {6 E! C
circuit test should be conducted at the exit of the wiring from the transformer. 6 I6 K/ J& q M6 o9 A4 G; I(N.B. Similar recommendations can be made for batteries and their protective devices)& J" V! |; J2 Q* D) d; ^( t6 O+ K
The overload test however must always be conducted after any secondary OVER-CURRENT - e# b$ M# v; f* c$ s2 d2 jPROTECTION device (conform clause 57.9.1b) providing that the conditions of sub-clause 1 _! G8 j9 m( z- b4 d9 p! v; o57.9.1. second dash are fulfilled. , ?9 |* h2 A {1 K3 S1 t! V " X' E! W4 V3 [" P( h; O7 f# d[attach]77107[/attach]3 W# F4 x) f5 E" Z# G8 H) K. X9 M2 U
DSH 401