The development of inductance formulae is mathematically complex and is the subject of many electrical engineering papers and books. To enable many of the normal busbar configuration inductances to be calculated for self and mutual inductances, the following formulae have been included.
It should be noted that self inductance LS is the inductance due to a single conductor, assuming that it is effectively outside the flux range of all other conductors. Mutual inductance M is the inductance resulting from the flux from other conductors.
Single Conductor
where
Ls = self inductance, mH
Ds = 0.2235 (a + b)
= g.m.d. (geometric mean distance from itself), cm
l = length of busbar, cm
Two Parallel Conductors
where
M = Mutual inductance, mH
Dm = g.m.d between bars
Obtain Dm from figure 18 or formulae at end of this Section)
l = length of busbar, cm
Go-and-Return Conductors
The inductance L per conductor includes both self and mutual components and therefore becomes equal to LS - M, i.e.,
where the conductor spacing is small compared with the conductor length, or
where b is small compared with d.
Single Conductor
Two Parallel Conductors
Go-and-return conductors
As before,
L = Ls - M
if the conductor spacing is small in comparison with its length and in comparison with d.
