Computation of eddy-current losses in cable sheaths and busbar enclosures

The usual method of calculating cable-sheath eddy-current losses gives satisfactory results for high-resistance sheaths but not for low-resistance sheaths. A method developed by Dwight for calculating this type of loss in unbonded busbar enclosures is applicable for low-resistance cable sheaths, but is not presented in a generalised form. A general method is given for the calculation of eddy-current losses in parallel and arbitrarily spaced thin tubes, some or all of which may contain other tubes. Two special cases are derived: one for three tubes equally spaced in triangular formation and the other for three tubes equally spaced lying in a plane. A table of loss factors has been prepared and deposited in the IEE Library. It covers wide ranges of two basic parameters, which enables it to be applied both to cable sheaths and busbar enclosures. Extracts from the table are given in the paper. It is shown that the finite wall thickness of the tubes can introduce appreciable additional losses, and an approximate formula for these is given.