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UL 2556中對絕緣耐壓測試有三種方式.8 B* v1 J2 q3 e( ?0 E
6.2 Dielectric voltage-withstand
$ X0 G+ \$ g+ Q" Y6.2.1 Scope
8 L- Y5 B5 g/ e! ^. XThis test establishes the methods for determining the dielectric voltage-withstand of a wire or cable.6 Z% \ i/ K; t/ E5 N- e3 z4 {
6.2.2 Apparatus& K! s0 P3 W3 Q: L! @5 K$ V' N1 S
The apparatus shall consist of
" e/ e W0 f( C1 g l$ \$ @" ca) an isolation transformer capable of supplying a test potential of 48 to 62 Hz, whose output
+ [. i3 s- s8 V" P7 hpotential is continuously variable from near zero to at least the specified rms test potential;
. r% V% F+ `' |: gb) a voltmeter having an accuracy of ±5%, on the high voltage side of the transformer. If
; G' b3 A) R: i, T" \8 R2 fanalog, it shall have a response time that does not introduce a lagging error greater than 1% of
& P5 a6 m; z* d+ k$ Tfull scale at the specified rate of increase in voltage;. ~" T( N1 ?' ?; m7 K
c) a fault current indicator;
* b/ z! i1 y0 ^+ M O+ o6 {0 k7 }d) a forced-air oven as described in Clause 4.2.3 Item (i), having insulated bushings for
5 G2 K3 \1 X1 }$ m/ B; J5 u4 |! nconnection of the test voltage while the oven is closed;) H7 \. N8 S& L& J1 L/ s
e) a temperature-measuring device with an accuracy of ±1 °C;
" }; P6 ~& z% _f) a tank filled with tap water; and
+ j& G" Q9 Z& T4 e" s' Lg) a means of grounding, maximum impedance of 15W.
. p$ x( g2 x9 E' M- Z) K) k1 S* c6.2.3 Preparation of specimens: X8 m9 n. @% R1 A. E7 P
6.2.3.1 Method 1 (in water)
- F. _/ a4 }; C( E7 d- H9 g5 PBoth ends of the individual conductors shall be made bare.
2 M- X: r- T3 [3 bIn preparing the wire for test, each end of the specimen shall be brought out well above the water level
6 o2 M( E/ X% e: din the tank, where applicable, and the covering removed from the surface of the insulation for a short
) p! v8 k3 o' C; J- _& P/ Jdistance if necessary to prevent surface leakage. The temperature of the water in which the specimen is5 K" p& }4 p. ^
immersed need not be controlled unless specified in the product standard.
" \" D* k: h: }5 BUnless specifically required by the product standard, a shielded or metal-covered single-conductor$ K) t6 m$ W7 F
specimen need not be immersed in water, the test voltage being applied between the conductor and the
) u B. |7 D8 t1 @! C9 Fshield or metal covering.
0 t- b# r& G+ b; PUnless specifically required by the product standard, a multiconductor cable need not be immersed in
* R5 z2 m! {# c1 Ywater, the test voltage being applied between each conductor and the electrode, consisting of all other
/ K: K r- Z2 p, l! Uconductors connected together and to all shields and metal coverings, as applicable.0 a, o9 K. N i0 ?9 X; R1 E, y
In all cases, the ends of the conductor of the specimen shall be spaced from the grounded electrode a
( F3 R6 i* H& [4 l0 s6 g' k4 p9 M* psufficient distance to prevent corona or flashover at the ends during application of the test voltage.8 ^& c/ t, d8 p' h% a. B" c6 u
6.2.3.2 Method 2 (in air)
& a1 Q! X& V1 f! n& m+ m$ xBoth ends of the individual conductors shall be made bare.
7 I' Z y! b2 ~+ P, B' WFor a single-conductor cable, a grounding electrode, when not present as a component, shall be applied.7 I: [; F. F3 W8 B' A: g' k3 I
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable.! a+ g! e. k, L$ p; O* N2 W
6.2.3.3 Method 3 (in air at elevated temperature)7 U5 X9 e7 f* p
Both ends of the individual conductors shall be made bare.8 X& r k! r( ?( [ S
For a single-conductor cable, a grounding electrode, when not present as a component shall be applied.
, V9 E7 n6 u7 q7 P) u$ i3 Z6 aA snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable. |
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