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UL 2556中對絕緣耐壓測試有三種方式.
5 M4 t# e. I a9 z$ W8 d. @6.2 Dielectric voltage-withstand
& ~; i" O) l! K& G0 J$ B+ H# R; o6.2.1 Scope' t. l2 o( {" F) x0 {
This test establishes the methods for determining the dielectric voltage-withstand of a wire or cable.
# ]/ h8 _/ a; M1 |) T$ v2 ?+ f1 q6.2.2 Apparatus' ~1 V( L. w" K X
The apparatus shall consist of
* \ M7 e3 X- oa) an isolation transformer capable of supplying a test potential of 48 to 62 Hz, whose output2 ]" |& A& I0 t& I
potential is continuously variable from near zero to at least the specified rms test potential;8 K: I% |4 X0 e6 y. W* q0 I4 W
b) a voltmeter having an accuracy of ±5%, on the high voltage side of the transformer. If
+ U4 }$ K8 N; ranalog, it shall have a response time that does not introduce a lagging error greater than 1% of
E! [+ a- M3 j6 bfull scale at the specified rate of increase in voltage;
1 i. T0 G5 ?7 ^c) a fault current indicator;
- f9 {+ f! q9 \, C2 q; H4 Od) a forced-air oven as described in Clause 4.2.3 Item (i), having insulated bushings for
+ f, `" [( |0 H' Qconnection of the test voltage while the oven is closed;
# i" \* ~$ e" k( d' x5 Le) a temperature-measuring device with an accuracy of ±1 °C;4 o6 M; W' z, l% p& I0 M
f) a tank filled with tap water; and
9 S9 m' j0 ]8 H: jg) a means of grounding, maximum impedance of 15W.5 \" u- r) `. ~6 P' l ~( P
6.2.3 Preparation of specimens
3 o& q' o% Z8 d! p' I6.2.3.1 Method 1 (in water)
/ ~$ `3 a( p) V+ T- m; _( L1 ~Both ends of the individual conductors shall be made bare.
Q3 w" E3 M7 Q" ~0 GIn preparing the wire for test, each end of the specimen shall be brought out well above the water level* u8 a( Z X" f7 S2 r0 X) q
in the tank, where applicable, and the covering removed from the surface of the insulation for a short
! n9 y: l& {% b) g1 z2 `8 qdistance if necessary to prevent surface leakage. The temperature of the water in which the specimen is' A( R$ f: z1 i& I4 |
immersed need not be controlled unless specified in the product standard." I* R3 G, i2 i& F
Unless specifically required by the product standard, a shielded or metal-covered single-conductor0 Q; g+ N9 u& c+ d; `! {
specimen need not be immersed in water, the test voltage being applied between the conductor and the
; ?) g& b/ L& y0 N! Oshield or metal covering.$ z. {( ?: q; ^' @! t
Unless specifically required by the product standard, a multiconductor cable need not be immersed in9 h( H: J, x, V C+ h
water, the test voltage being applied between each conductor and the electrode, consisting of all other* f0 y) I" b6 v, i7 G
conductors connected together and to all shields and metal coverings, as applicable.
! E a% C7 f: [In all cases, the ends of the conductor of the specimen shall be spaced from the grounded electrode a
( _2 h- @6 J2 Rsufficient distance to prevent corona or flashover at the ends during application of the test voltage.
4 U5 i8 Z5 H8 e8 w. |( |6.2.3.2 Method 2 (in air)
' X( } O( N0 v+ ]0 N3 z3 p- iBoth ends of the individual conductors shall be made bare.5 e7 g) X: g# I' j* f( k4 F
For a single-conductor cable, a grounding electrode, when not present as a component, shall be applied.
8 c6 M2 ~8 G# @A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable.
5 o4 p ~; V5 Y" o3 J2 a v8 [6.2.3.3 Method 3 (in air at elevated temperature)
4 M' J& {: g1 fBoth ends of the individual conductors shall be made bare.
, _) O6 }, C iFor a single-conductor cable, a grounding electrode, when not present as a component shall be applied.) j1 U4 a& G( m5 ?
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable. |
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