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UL 2556中對絕緣耐壓測試有三種方式.7 f# P" s' d# Y# i2 t
6.2 Dielectric voltage-withstand
& ~& x) @( S9 X, p! v* U; T6.2.1 Scope# h, {1 K8 e& [2 D) e# @2 e
This test establishes the methods for determining the dielectric voltage-withstand of a wire or cable.0 L" l( y4 ~ X7 C
6.2.2 Apparatus
1 y' S( C$ O" C5 Q. @The apparatus shall consist of ], M2 [9 {0 p: U
a) an isolation transformer capable of supplying a test potential of 48 to 62 Hz, whose output, [' b/ ]% J, V6 T G3 |# I Q
potential is continuously variable from near zero to at least the specified rms test potential;
1 k& f8 p8 N4 X' e$ |: L; gb) a voltmeter having an accuracy of ±5%, on the high voltage side of the transformer. If; r' `/ b/ R3 o& `6 B# n" N3 {
analog, it shall have a response time that does not introduce a lagging error greater than 1% of
1 G! U% {* G* y1 ^0 R$ ?full scale at the specified rate of increase in voltage;: t1 ^1 l- y- ~% G+ i
c) a fault current indicator;6 m: Z6 u1 {2 l
d) a forced-air oven as described in Clause 4.2.3 Item (i), having insulated bushings for
' w6 p U# e1 k" w T2 {" |' jconnection of the test voltage while the oven is closed;
1 X* l4 B+ E3 n! @- g- f. V& ye) a temperature-measuring device with an accuracy of ±1 °C;- x4 R$ Z$ ?: d) _/ c; ^) b$ }* @5 E
f) a tank filled with tap water; and* J7 j- c' L) O" i
g) a means of grounding, maximum impedance of 15W.% M( k( q# Y% F. h; s$ I
6.2.3 Preparation of specimens
& D; K6 X4 [' K" K# X6.2.3.1 Method 1 (in water)
% B4 h X7 J! D9 K4 M) U+ [Both ends of the individual conductors shall be made bare.& G: g7 k, O4 l3 h6 L9 [. Q
In preparing the wire for test, each end of the specimen shall be brought out well above the water level
7 S9 u% u4 Y/ R& a2 C& ^in the tank, where applicable, and the covering removed from the surface of the insulation for a short
4 d( _. M1 L# i2 s8 H! c1 F: Fdistance if necessary to prevent surface leakage. The temperature of the water in which the specimen is
% J( w, X0 N2 |7 E8 l$ _7 a# Cimmersed need not be controlled unless specified in the product standard.; _( T8 z/ o; `
Unless specifically required by the product standard, a shielded or metal-covered single-conductor7 {, B1 L( Q. O) r6 c. T
specimen need not be immersed in water, the test voltage being applied between the conductor and the* M0 ~5 v9 ?* b% g
shield or metal covering.
' t# f( a. w& j: L0 ?Unless specifically required by the product standard, a multiconductor cable need not be immersed in
, N7 r+ T9 p) K; B+ {; Jwater, the test voltage being applied between each conductor and the electrode, consisting of all other2 m, f5 j; ^8 S- I
conductors connected together and to all shields and metal coverings, as applicable.' v' Q) M# t. Z+ [0 f
In all cases, the ends of the conductor of the specimen shall be spaced from the grounded electrode a
! h# @" z- h; e; N3 |; ssufficient distance to prevent corona or flashover at the ends during application of the test voltage.
0 ~9 o* u; G4 y' b x6.2.3.2 Method 2 (in air)
T: G) M) T) @$ {: ^0 ZBoth ends of the individual conductors shall be made bare.
. O* t) A( l( i' bFor a single-conductor cable, a grounding electrode, when not present as a component, shall be applied.6 E( \+ Q( h& W2 Q
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable.6 \$ h+ ~& P) q# t' i) b+ o+ Z
6.2.3.3 Method 3 (in air at elevated temperature)9 L+ N8 P8 D3 Z" ~# B* p$ s
Both ends of the individual conductors shall be made bare.& c' A( D3 k5 v7 A
For a single-conductor cable, a grounding electrode, when not present as a component shall be applied.9 H" F* Z4 L9 C4 m5 D
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable. |
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