THEORETICAL ANALYSIS OF A DC SATURABLE-REACTOR GROUND-FAULT PROTECTION SYSTEM.

Saturable-reactor systems are commonly used for dc ground-fault protection in the coal mining industry. However, the operation of these systems has only been described qualitatively. An initial analysis to aid in the future design of more-sensitive relaying schemes is presented. A mathematical model that predicts the general response of the ac excitation current to a steady-state dc ground-fault current is developed. Two expressions for flux linkages are obtained and set equal to each other. The magnetization curve of the reactor core is represented by a hyperbolic approximation. The ac excitation current is then determined for various magnitudes of dc ground-fault current by numerical iteration. The resulting waveforms for two examples are plotted, and the rms values of current are calculated.