Page 930 - Industrial Power Engineering and Applications Handbook

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Conductor spacing - 2 -
0
0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5
Semi perimeter a + b
1. For 3-4 systems read reactance against + [ .26 -
asb]
I ,
2. The reactance varies with the ratio $- and therefore there may be a number of possible busbar combinations and the corresponding
< I
curves for different a However, only a few curves have been drawn for the likely minimum and the maximum values of a Since the
b’
b’
variation is not large therefore by interpolation the more pertinent value of reactance can be determined from these curves.
Figure 28.19(a) Reactance of rectangular busbars at 50 Hz on account of proximity effect
Rectangular sections (Figure 28.19(a))
280
Thc rcactancc is drawn as a function of
260
Centre snacing (‘S?
240 ~
Semi-perimeter (a + b)
220
At lower spacings this value will be influenced by the
- width (b) and the thickness (a) of the conductor. At lower
200
spacings, therefore, proximity curves are different for
different ratios of a/b whereas for larger spacings they
6 180 approach the same curve.
&160 When more than one section is used together, to make
2
.. larger ratings, all the sections of one phase may be
$140
considered to be one large section. The dimensions a
8 120 and b of the whole section are now considered as one
C conductor, as illustrated in Figure 28.8.
,m
8 100 The reactance thus obtained can be doubled for single-
c? phase systems. For a three-phase system the configuration
80
of the three phases with respect to each other will play a
60 significant role and the linear centre spacing S has to be
modified to an effective or geometric mean spacing S,,
40 where
20 s, = (Sa ‘ Sb ’ S,)”3 (28.7)
Conductor spacing Se between centres (em) - For configuration (a) of Figure 28.20
i
Itm i i FH i i i i i i i i i i i i ti iI
0 20 40 60 80 100 120 sa = Sb = s
Figure 28.19(b) Reactance of tubular busbars for single-
phase or three-phase systems at 50 Hz s, = 2s