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UL 2556中對絕緣耐壓測試有三種方式.' U4 h2 {" s$ S- j c; Z! w* ^
6.2 Dielectric voltage-withstand
9 {* ]1 N" I: Z. h$ K3 w6.2.1 Scope
9 ^1 B" q2 h$ o, T2 n7 ?This test establishes the methods for determining the dielectric voltage-withstand of a wire or cable.
. M6 ~# l- o! m1 p) m6.2.2 Apparatus; _" l$ w9 Y& E( K/ u6 U
The apparatus shall consist of
y# E) u: C2 a$ X% ja) an isolation transformer capable of supplying a test potential of 48 to 62 Hz, whose output
) j# r& b& @6 f: a+ @( gpotential is continuously variable from near zero to at least the specified rms test potential;" T1 } y/ b/ h% e
b) a voltmeter having an accuracy of ±5%, on the high voltage side of the transformer. If
2 v) I7 f! A5 b2 k# @' Z1 Qanalog, it shall have a response time that does not introduce a lagging error greater than 1% of
8 Q/ c4 r7 @( T, @full scale at the specified rate of increase in voltage;! }9 T3 f {, ?" ?: W
c) a fault current indicator;
& |/ t' {6 ^8 v2 ~ I1 kd) a forced-air oven as described in Clause 4.2.3 Item (i), having insulated bushings for
2 [6 G. f# X! z- S0 G0 [% Kconnection of the test voltage while the oven is closed;
! j% {6 D# e- ~4 y5 Re) a temperature-measuring device with an accuracy of ±1 °C;
* z/ n3 P$ f. S: |* U( }f) a tank filled with tap water; and+ B, Y6 b% Q, O% l& B3 Q
g) a means of grounding, maximum impedance of 15W.
9 n; ^! L# G/ A- h6.2.3 Preparation of specimens, [* N& {0 E2 D* Q; F
6.2.3.1 Method 1 (in water)
C5 K' v8 N) t, [7 D( S: IBoth ends of the individual conductors shall be made bare.
$ W1 r- ^: n; U* t( VIn preparing the wire for test, each end of the specimen shall be brought out well above the water level3 R+ E1 _6 L1 ] i- U7 s2 x( o
in the tank, where applicable, and the covering removed from the surface of the insulation for a short& v2 x2 x% y9 |" b2 N
distance if necessary to prevent surface leakage. The temperature of the water in which the specimen is
$ C/ m6 l! N* x- ~$ x; m. t) N; Zimmersed need not be controlled unless specified in the product standard.
: F0 N @8 c r$ ~8 I0 z$ \Unless specifically required by the product standard, a shielded or metal-covered single-conductor d. F. p. C; g% J: L& x+ w
specimen need not be immersed in water, the test voltage being applied between the conductor and the
) `, {2 r; |5 r" Fshield or metal covering.
@! b9 E0 q3 v& ?# Z" oUnless specifically required by the product standard, a multiconductor cable need not be immersed in9 ~4 C a. q9 ]& T" }; g1 I2 z
water, the test voltage being applied between each conductor and the electrode, consisting of all other
" ^" v0 i9 [; X( Zconductors connected together and to all shields and metal coverings, as applicable.
7 Q+ i: _$ ] v) z& r t# ^* BIn all cases, the ends of the conductor of the specimen shall be spaced from the grounded electrode a
( C+ h M! B- ^' p" Csufficient distance to prevent corona or flashover at the ends during application of the test voltage.
" H, o P1 |- q4 o q) f6.2.3.2 Method 2 (in air)
, n, n; U, Y% i9 ^( C1 XBoth ends of the individual conductors shall be made bare.
v8 \1 F r6 LFor a single-conductor cable, a grounding electrode, when not present as a component, shall be applied.- O% L5 Z! c( H+ }4 Z, b! O. d
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable.
$ D$ f Y1 s2 Y. w6.2.3.3 Method 3 (in air at elevated temperature)5 f6 o' l6 G0 l
Both ends of the individual conductors shall be made bare., e7 q+ S% }2 w4 p# a
For a single-conductor cable, a grounding electrode, when not present as a component shall be applied.# F V R% M# {2 I i! s. M( ?+ Z
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable. |
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