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UL 2556中對絕緣耐壓測試有三種方式.6 b C7 f C# [% r) z& r- `% z
6.2 Dielectric voltage-withstand7 J$ e) f7 I- ?" y
6.2.1 Scope$ }- F0 j1 i: S% R/ c; w# A
This test establishes the methods for determining the dielectric voltage-withstand of a wire or cable.
% w4 @7 u4 q$ Q) n0 K6.2.2 Apparatus
; ~* H' a8 v$ Q% rThe apparatus shall consist of
. y/ r. b) }$ I- r9 P' i& da) an isolation transformer capable of supplying a test potential of 48 to 62 Hz, whose output; i1 v: g3 b- m7 ^
potential is continuously variable from near zero to at least the specified rms test potential;
( |+ f& c+ W) a' bb) a voltmeter having an accuracy of ±5%, on the high voltage side of the transformer. If
. U2 g; I# d% U/ F6 R$ Ranalog, it shall have a response time that does not introduce a lagging error greater than 1% of9 o! r0 p) M8 N0 K* C! Q! v
full scale at the specified rate of increase in voltage;5 ]4 s$ `- }' [& Q) y+ [) H; \: E
c) a fault current indicator;
9 y1 Q E+ q$ Z1 N! qd) a forced-air oven as described in Clause 4.2.3 Item (i), having insulated bushings for
e! P1 {+ N/ E' q9 U* J" O7 gconnection of the test voltage while the oven is closed;( i6 ~; O# T$ y# w' E
e) a temperature-measuring device with an accuracy of ±1 °C;7 b) t' X8 s2 n& W1 n' M
f) a tank filled with tap water; and
9 Z$ v( ^1 a( a8 Wg) a means of grounding, maximum impedance of 15W.! d% E& y2 s, Z5 S% E
6.2.3 Preparation of specimens6 K6 h/ w4 f3 w5 k
6.2.3.1 Method 1 (in water)
5 {+ U. l) Y5 j' v5 l1 L& w; u2 mBoth ends of the individual conductors shall be made bare.. [( q J# W9 u+ b1 @/ u+ e
In preparing the wire for test, each end of the specimen shall be brought out well above the water level& x/ A, S( z# t) N1 _- z: w
in the tank, where applicable, and the covering removed from the surface of the insulation for a short
5 Z& U) e1 ?. a) }/ t- p Cdistance if necessary to prevent surface leakage. The temperature of the water in which the specimen is
6 s" h( c; S5 I$ D6 f {& _immersed need not be controlled unless specified in the product standard.2 _& o4 H5 p4 r% K
Unless specifically required by the product standard, a shielded or metal-covered single-conductor
5 ^/ h4 V' Q1 tspecimen need not be immersed in water, the test voltage being applied between the conductor and the
; _8 Z- o& p' F3 R0 vshield or metal covering.; A8 J5 P3 C8 L: @9 @" |. z: {
Unless specifically required by the product standard, a multiconductor cable need not be immersed in
g- i& C( h" Y+ p0 J1 X# l/ Cwater, the test voltage being applied between each conductor and the electrode, consisting of all other8 l+ X/ S o9 ^1 m. O( i
conductors connected together and to all shields and metal coverings, as applicable.
0 e. X4 g' a2 I2 kIn all cases, the ends of the conductor of the specimen shall be spaced from the grounded electrode a
( Q0 I$ O& o$ hsufficient distance to prevent corona or flashover at the ends during application of the test voltage. O! ~0 P7 r, ^$ X8 B" W4 Y
6.2.3.2 Method 2 (in air)0 Q) N2 J& N: k% Z) N0 Z
Both ends of the individual conductors shall be made bare.
2 W# R9 C/ ^* ]3 Q. y9 oFor a single-conductor cable, a grounding electrode, when not present as a component, shall be applied.# Y, a2 g. K |- \8 w; D) o
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable.7 c; A* x5 |; p; o! U
6.2.3.3 Method 3 (in air at elevated temperature)$ B4 o! K( t8 r# a+ F: o
Both ends of the individual conductors shall be made bare.
: R% b2 Y- ]( s0 ~ B5 H) QFor a single-conductor cable, a grounding electrode, when not present as a component shall be applied.
1 s* V. g5 z- s6 HA snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable. |
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