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EN 61242中关于线盘的接地电阻的测量中,有如下规定:
& ^ L J2 \/ |- T( Q/ S6 f( T9.7 Internal earthing circuit in cable reels, including any joints contacts and the like, shall be of low
" d5 _) |$ v2 @% } s' r/ pelectrical resistance.
5 N" Y1 t8 S) X# M) O$ ]6 [4 u5 TCompliance is checked by the following measurement which is made after the test specified in Clause 21.3 x* d3 O7 i2 Y# Q) q7 c
A current derived from an a.c. source, having a no load voltage not exceeding 12 V, and equal 1.5 times rated
, m+ r& z& v' o& @% R# \" w/ Bcurrent of the cable or 25 A, whichever is the greater, is passed through the earthing circuit.# A( w7 L+ v* L
The voltage drop is measured and the resistance calculated from the current and this voltage drop.: D5 T$ A& Y" q
The resistance shall not exceed 0,05 Ω..
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. O; E: n8 Y7 U测量时,发现如果包含其线盘所带的电缆在内测接地电阻,是绝对大于0.05的,而且主要的电阻产生于电缆本身, 0 d) [9 r) r7 u; I8 v5 Y
我知道在60335中测接地电阻时将电源线是排除在外了的,但是在这个标准里面并没有提到这一点,但是考虑到一般电缆在一定长度下也达不到0.05的限值,那是否意味着这时也应将电源线排除在外呢?但有个问题就是,如果将电源线排除,那么绞线盘的接地电阻还有什么意义呢?
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希望大家能讨论一下,指点迷津..谢谢~!! |
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