The Calculation of DC Fault Currents with Contributions from DC Machines and Rectifiers

Since 1970 at least 12 men have died from underground coal mine fires which were started due to undetected high-resistance dc faults on trolley systems. A technique is proposed which utilizes Newton´s method to solve the nonlinear equations which determine such fault currents. The formulation is unique in that it is the first known method to account for dc fault current contributions from both rectifiers and dc motors. Results from the technique can be used to size and coordinate devices used for system protection. The problems of accurately predicting such fault currents is discussed. A sample problem is included as an example.