Mains supply transformers: Short Circuit and Overload tests + C" n' n" K0 v# I! x
57.9.1 5 [) l4 v* B) t- _) ?
60601-1(ed.2);am1;am2 $ ]: {! l2 f6 D+ U/ c! I; t
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Standard(s)- (year and edition): 4 d% A( |& c; t" K9 U. rIEC 60601-1:1988 Ed.2 Am1+Am2$ r: X4 {1 z$ R3 t
Sub clause(s): 57.9.13 b: e" l$ }8 v
Sheet n°: DSH-401 E; ~! v; W4 l; }% N* @. U2 F0 ESubject: Mains supply transformers: Short Circuit and Overload tests v3 q& |1 ~! ]! @5 f9 {9 M1 U& Q
Key words: Over-current, protection, overload$ O3 I% O5 y' R! o. {# x# b W: r+ `
Confirmed by CTL at its 39th meeting, in Cologne8 `2 R* o; H) j' n ^& A$ d
Question:9 V, s- A8 ]7 H! w1 b( V4 I( x
Secondary circuit OVER-CURRENT PROTECTION is the first active component on the+ ]3 C0 r6 f0 Z0 L: c
secondary side of a mains supply transformer. Is the overload test performed before or after the$ n( e/ N+ }. }- B o* i/ X( n
fuse? - H% r" U! v5 P8 I# ~( a- [ ?Insufficient transformer winding crossover insulation and secondary circuit CREEPAGE + u! @( D# b/ K+ h3 z% d' k# NDISTANCES and AIR CLEARANCES causes transformer winding to short-circuit and exceed 0 _6 w8 u; r# |) B: Z6 d1 pallowable temperatures. * z2 e5 r; A: i( f0 ]" r( ]* n- KDecision: / t3 @5 E0 L# u- ?9 l6 {5 _If the possibility of a short-circuit exists before the secondary OVER-CURRENT PROTECTION , Q6 |3 U: `: \; z0 M1 Z) W8 Ldevice (e.g. failure of basic insulation between winding or detachment of the wiring) the short 6 h% U4 {8 N1 F, }4 D3 `circuit test should be conducted at the exit of the wiring from the transformer.5 W+ q; _3 X5 y1 r' C+ n# h1 @
(N.B. Similar recommendations can be made for batteries and their protective devices) 8 U3 q4 q) S8 E0 JThe overload test however must always be conducted after any secondary OVER-CURRENT, N4 Y; U4 G- Z2 L8 m
PROTECTION device (conform clause 57.9.1b) providing that the conditions of sub-clause 1 v2 [) f* y7 @57.9.1. second dash are fulfilled.% ?! H# V# X6 A) c
DSH 401