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发表于 2010-1-6 09:40
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引用第1楼yanfenghmm于2010-01-06 09:17发表的  :
8 p9 }# x0 Q/ P. T标准应该有具体要求吧。 文字的要求有时是含混不清的,要看读者的理解呀
9 A1 G9 `# S! V2 b6 N下面是table 4:% @1 Z, h/ a$ }7 z( y+ C0 Y$ z
.) g( C8 x1 W4 Q; K
3 ?6 g+ e& `* b% t' V" U1 v9 l- s6.7.1.1 CLEARANCES
' P$ m4 }3 t) U) A1 s6 x3 hCLEARANCES are specified to withstand the maximum transient overvoltage that can be
8 N2 M8 C n$ b% a; {present on the circuit, either as a result of an external event (such as a lightning strike, or a5 ]2 @* |! {0 f$ k* O
switching transient), or as the result of the operation of the equipment. If transient- X9 D- F( q% o3 g0 m, \
overvoltages cannot occur, CLEARANCES are based on the maximum WORKING VOLTAGE.
: m* \; s, T$ d2 S* F5 W) AThe value for CLEARANCE depends on
& s/ x {8 h+ W/ I. `a) the type of insulation (basic insulation, reinforced insulation, etc.);
1 {$ p" u1 p# R, U* [" X, Yb) the POLLUTION degree of the micro-environment of the CLEARANCE.1 }% ]5 ~( H l5 `
5 T: o6 W, X o6.7.1.2 CREEPAGE DISTANCES
3 G" I0 z5 M/ f0 F ^For CREEPAGE DISTANCES between two circuits, the actual WORKING VOLTAGE which stresses
) D" e2 W. A8 Y! n# l9 H: tthe insulation between the circuits shall be used. Linear interpolation of CREEPAGE DISTANCE is# r* j Q* y" ?) {: a0 R4 d
permissible. CREEPAGE DISTANCE shall always be at least as large as the value specified for5 i& X. e Q4 N5 b" a2 U( N* @: F
CLEARANCE.8 a4 M D7 X( D
) z3 F4 P w0 w! t
一般而言电气间隙被设计为耐受最高瞬时过电压,经常会考虑工作电压峰值带来的影响;而爬电距离被认为是耐受工作电压有效值的。
- F- j" s, E) ~从上面两大块文字中,该标准中6.7.1.1看不出电气间隙要考虑工作电压(peak or rms)的要求,但6.7.1.2爬电距离明确说明要考虑工作电压。而table 4中第一列表头只写了"Voltage line-toneutral# r) X7 J7 C8 }5 `+ ]
a.c. r.m.s. or d.c.",也没有提"working voltage"。所以实际查表时我就犯难了,到底如何操作呢,请高手指教! |
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