Solid Short Circuit of D-C Motors and Generators

In this paper the current of d-c machines on solid short circuit is expressed in terms of constant impedances similar to X
_d
' and x
_d
for synchronous machines. The outstanding advantage of this new result is that any number of d-c machines may be included in a network, with or without connection of batteries, rectifiers, or other machinery, and calculations may be made using a network analyzer, d-c calculating board or numerical calculation. The current in any machine, the total fault current, and so on, can be determined. Equations are given for d-c machines which are similar to the well-known equations for synchronous machines. Equations are given for the transient and steady-state resistances and for the decrement factors. The latter factors determine the rise and subsequent decline of current. Direct and simple expressions are given for the maximum rate of rise of current and for the maximum or peak value of current. Although design data is required for reliable calculations, useful preliminary estimates of current can be made using no data other than the resistance of the machine windings and a few dimensions which can be obtained from simple inspection of the machines. For this purpose, generalized values for design constants are given in the nomenclature.