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UL 224 是绝缘套管标准,其5.6条款对击穿电压和测试方法有明确要求。6 {( b' x, _5 c
5.6 Dielectric voltage withstand and breakdown9 a* d) ^5 X1 E3 O+ J2 t
5.6.1 Aged and unaged tubing shall be capable of withstanding, without breakdown, the application of a 60 Hz essentially sinusoidal potential of 2500 V applied for a period of 1 minute between a conductor or conductors inserted in the tubing and strip metal foil wrapped around the outer surface of the tubing. Thepotential shall then be increased until breakdown occurs. The breakdown potential of tubing that has been aged as indicated in Item 9 of Tables 7 to 32 or after 7 days at the temperature determined from the formula in Clause 5.3.7.9, as applicable, shall be at least 50 percent of the breakdown potential of the
! Q) W' _, f5 x8 z& o' |unaged tubing, but not less than 2500 V.. ]2 X0 {! j4 }; {' _
5.6.2 Three specimens of tubing, each 460 mm (18 in) in length, shall be aged in a circulating-air oven as indicated in Item 9 of Tables 7 to 32 or after 7 days at the temperature determined from the formula
4 Y$ D7 a* m# a+ Q$ gin Clause 5.3.7.9, as applicable, and shall then be cooled to room temperature. These and similar specimens conditioned for the same length of time at a temperature of 23.0 ±2.0 °C (73.4 ±3.6°F) shall! W: D! T) }0 I6 `% p
be tested. One clean, straight, bare, solid, copper conductor shall be inserted with a snug fit into each specimen of 0.305 to 3.88 mm (0.012 to 0.153 in) tubing prior to aging. Several conductors shall be
3 b3 t; D3 N. M ~! kinserted with a snug fit into 3.89 mm (0.154 in) inside diameter or larger tubing. Heat-shrinkable tubing shall be centred and recovered on a conductor or conductors having the same overall diameter as the
1 N, L- F# [" Nmaximum recovered inside diameter of the tubing being tested (including adhesive for tubing with meltable liner, as specified by the manufacturer). The centre 152 mm (6 in) portion of each specimen shall be' `( Q4 }# I! t' b; H1 i8 i* L
wrapped with strip metal foil.
( F6 n f: {' R+ J5.6.3 Each specimen shall be stressed by means of a testing transformer whose output potential is continuously monitored by an acceptable voltmeter that is connected in the output circuit and directly and5 g* q0 a+ K, L9 I8 b
precisely indicates the potential being applied to a specimen, is essentially sinusoidal at 50 to 60 Hz, and can be varied continuously from 0 to at least 2500 V. The applied potential shall be increased from zero at an essentially uniform rate that is not less than 100 percent of the voltage rating for the product in 60 seconds, and not more than 100 percent in 10 seconds (the rate of increase shall not exceed 500 V/s in any case). The increase shall continue in this manner until the voltage reaches 2500 V. If this level is reached without breakdown, the potential shall be held constant at 2500 V for 60 seconds and shall then
3 o" w( i5 _1 }5 Kbe increased at the rate mentioned above until breakdown occurs. |
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