Abstract: A power-distribution system can detect a transmission-line electrical fault, and the power source can be electrically isolated from the transmission line before a human or equipment is substantially harmed or damaged. A controller on the source side is responsive to one or more sensors that provide a signal indicative of the voltage across the transmitter side of the transmission line. A source-disconnect device operable by the controller electrically isolates the source from the transmission line. A signal-generator circuit is configured to superimpose a higher-wavelength carrier waveform with the source-output waveform on the transmission line. The controller determines the normal impedance of the transmission line from measurement and detects a transmission-line fault, as indicated by a change in carrier waveform reflections or energy content of the carrier waveform and generates a command to open the source-disconnect device upon detection of the fault.