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UL 2556中對絕緣耐壓測試有三種方式.# m+ }( D1 W- L% G2 `) r
6.2 Dielectric voltage-withstand) U# x& o. F O P
6.2.1 Scope
& Q) W, a$ Z% bThis test establishes the methods for determining the dielectric voltage-withstand of a wire or cable.
9 m8 L0 R. o" P- A6.2.2 Apparatus
! O9 x6 V! X' K6 f: }The apparatus shall consist of
& S; p8 E* C9 s1 H; i K- K, Q/ ], na) an isolation transformer capable of supplying a test potential of 48 to 62 Hz, whose output
* a: U: L) u# j" N' B% u7 kpotential is continuously variable from near zero to at least the specified rms test potential;
% q s* d, n$ w J7 N, [( N6 Ob) a voltmeter having an accuracy of ±5%, on the high voltage side of the transformer. If; y" |. J- ~5 L3 v) `
analog, it shall have a response time that does not introduce a lagging error greater than 1% of; ]5 C: z( E8 l6 ~8 q- L
full scale at the specified rate of increase in voltage;
) y3 A" W0 q. E" ?c) a fault current indicator;
3 q: ~1 N' j3 @' j1 r2 Y, [d) a forced-air oven as described in Clause 4.2.3 Item (i), having insulated bushings for# Y. K1 Q. {: x
connection of the test voltage while the oven is closed;
$ w- P* f9 n8 d+ A" B6 f$ G me) a temperature-measuring device with an accuracy of ±1 °C;2 y7 T. c% M" W3 R
f) a tank filled with tap water; and
1 \: F, V5 p' B1 j0 D: O9 ^# K6 _g) a means of grounding, maximum impedance of 15W.6 S$ C, Z3 a0 S; V0 ^7 }3 ^6 }# i" U
6.2.3 Preparation of specimens6 X+ c/ r5 b5 x3 i l
6.2.3.1 Method 1 (in water)$ g0 o1 u5 @2 ]# o; N( j. [" ~$ d
Both ends of the individual conductors shall be made bare.
1 r" G; o' d k3 xIn preparing the wire for test, each end of the specimen shall be brought out well above the water level9 l5 W! o+ |& b* |- U; T1 y
in the tank, where applicable, and the covering removed from the surface of the insulation for a short* r$ h9 P' |' E. ?+ e
distance if necessary to prevent surface leakage. The temperature of the water in which the specimen is
, I+ [3 p% w K( O, x8 p$ _8 ]immersed need not be controlled unless specified in the product standard.$ o7 u$ \0 o. h9 H
Unless specifically required by the product standard, a shielded or metal-covered single-conductor
- k5 K2 s5 Y# H" t E. V& ]specimen need not be immersed in water, the test voltage being applied between the conductor and the
( L& d5 F @6 N: Y; E. h) K8 Jshield or metal covering.
$ k" s( u! q5 X: f7 I' l aUnless specifically required by the product standard, a multiconductor cable need not be immersed in3 x) y5 j' J$ W/ `
water, the test voltage being applied between each conductor and the electrode, consisting of all other3 h: t2 e* m: J+ W
conductors connected together and to all shields and metal coverings, as applicable.7 V, ?& O0 }6 y0 ]/ M
In all cases, the ends of the conductor of the specimen shall be spaced from the grounded electrode a
6 t4 D6 \! h2 U+ [) W, Xsufficient distance to prevent corona or flashover at the ends during application of the test voltage.
0 p' g& y9 a! k6.2.3.2 Method 2 (in air)
0 ?: @% W: J7 `6 ZBoth ends of the individual conductors shall be made bare.& P/ S ?, n+ c+ p$ {* l- x
For a single-conductor cable, a grounding electrode, when not present as a component, shall be applied.2 _3 b- t3 E# X
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable., Z5 P( X8 r$ U2 a) y6 n5 V: V
6.2.3.3 Method 3 (in air at elevated temperature)
. u+ p: F, Z0 \- d: R3 p, X" \Both ends of the individual conductors shall be made bare.6 Y+ W/ O: R& u% r- t; Y. i
For a single-conductor cable, a grounding electrode, when not present as a component shall be applied.! P5 s/ m2 E4 }2 l- ?8 q
A snug-fitting close-weave copper braid, a metallic tape, or graphite have been found to be acceptable. |
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