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UL 2556中對絕緣耐壓測試有三種方式.1 L& X# M5 H! [) S' I5 |
6.2 Dielectric voltage-withstand# i* w8 N% ?; f( M3 M
6.2.1 Scope; S, T% U/ e* X
This test establishes the methods for determining the dielectric voltage-withstand of a wire or cable.
" U) `+ \: y! y* m( ^0 d6.2.2 Apparatus$ t9 j; Y8 a, x: {( [
The apparatus shall consist of) L# _. E0 x# i
a) an isolation transformer capable of supplying a test potential of 48 to 62 Hz, whose output
' f+ Q6 s9 f: g6 zpotential is continuously variable from near zero to at least the specified rms test potential;
+ m& Y+ j2 S( b# d' A# Z6 F& v& Gb) a voltmeter having an accuracy of ±5%, on the high voltage side of the transformer. If
" k! n$ V7 E8 Ranalog, it shall have a response time that does not introduce a lagging error greater than 1% of$ m6 U; W$ e: C! l7 }7 A# g$ J# Z& ~
full scale at the specified rate of increase in voltage;
8 b* M* b7 k4 r+ `. Wc) a fault current indicator;+ t V! p2 f' `3 \0 ^- Y5 E- v
d) a forced-air oven as described in Clause 4.2.3 Item (i), having insulated bushings for: h4 Z) o' S: f1 H8 `: \
connection of the test voltage while the oven is closed;
# i4 ^, N! a' c- l/ Me) a temperature-measuring device with an accuracy of ±1 °C;2 n3 j7 t8 i- `+ i+ h* J
f) a tank filled with tap water; and
4 {' T6 B, |2 ~g) a means of grounding, maximum impedance of 15W.
2 e& F6 K$ h" S9 P6.2.3 Preparation of specimens
- s0 a: n+ r, g6.2.3.1 Method 1 (in water)$ s* A! g- v9 `. a0 Q
Both ends of the individual conductors shall be made bare.9 `7 }& f2 v3 M
In preparing the wire for test, each end of the specimen shall be brought out well above the water level
: c5 N* ~( x. X8 xin the tank, where applicable, and the covering removed from the surface of the insulation for a short8 `+ ^! d4 A. y k0 p8 O5 o1 x/ d+ S
distance if necessary to prevent surface leakage. The temperature of the water in which the specimen is
7 t% R& Z, C" j" k/ ` l5 Yimmersed need not be controlled unless specified in the product standard.
- v' S4 V/ M% @% x7 B. [+ c$ FUnless specifically required by the product standard, a shielded or metal-covered single-conductor! B+ e% A: N8 [% {4 b0 z9 o
specimen need not be immersed in water, the test voltage being applied between the conductor and the
: I9 f6 A6 U, m, X Q7 U; Ishield or metal covering.8 C0 x& `! S9 L0 \+ R. }# V9 |6 d; Q
Unless specifically required by the product standard, a multiconductor cable need not be immersed in# f$ f, m9 X' d2 A( A0 N E
water, the test voltage being applied between each conductor and the electrode, consisting of all other
( e: G v8 b. R3 fconductors connected together and to all shields and metal coverings, as applicable.8 ~) `4 e. {% T
In all cases, the ends of the conductor of the specimen shall be spaced from the grounded electrode a, C) o/ K! B( l1 V. _9 a
sufficient distance to prevent corona or flashover at the ends during application of the test voltage.; j, C& w/ _# U' R2 t
6.2.3.2 Method 2 (in air)1 M9 X6 r$ `$ ^ u! A! S
Both ends of the individual conductors shall be made bare.
/ _4 z# P* H& KFor a single-conductor cable, a grounding electrode, when not present as a component, shall be applied.
- T+ o0 S! A N! \! O; }A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable.
$ j. s) d O/ d0 { @6.2.3.3 Method 3 (in air at elevated temperature)- W& s, E p0 F7 g: M- X
Both ends of the individual conductors shall be made bare.
4 P& l9 u% }2 ~( i- p4 \6 YFor a single-conductor cable, a grounding electrode, when not present as a component shall be applied.6 M- N1 j, U' q! G% P
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable. |
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