Method and apparatus for monitoring isolation of an electric power bus

Dynamically monitoring of an electrically-isolated power bus for a DC power system is described, and includes dynamically monitoring voltage and current on the power bus to determine a variation in the voltage on the power bus. When the variation in the voltage on the power bus is less than a threshold, an active positive isolation resistance term and an active negative isolation resistance term are determined. A first voltage balance term is determined based upon a ratio of the active positive isolation resistance term and the active negative isolation resistance term. A dynamic positive isolation resistance term and a dynamic negative isolation resistance term are determined based upon the active negative isolation resistance term. A fault associated with the power bus is determined based upon the dynamic positive isolation resistance term and the dynamic negative isolation resistance term.