Power line carrier impedance matching monitor

This paper describes an impedance matching monitor for use with power line carrier systems on high voltage transmission lines. The purpose of the monitor is to determine when an undesirable impedance mismatch between a carrier transmitter and its load occurs, and to provide an alarm when the condition occurs. The alarm output is based on a calibrated setpoint that corresponds to some given percent reflected power level, or reflection coefficient, as opposed to an actual calculation of percent reflected power or reflection coefficient for a given impedance mismatch. That is, the system is calibrated with known impedance that results in the reflection coefficient that yields the desired percent reflected power alarm point. The monitor developed consists of two key components, which are a directional coupler and a controller. The impedance matching monitor was successfully installed on a PLC system used with a directional comparison blocking protection scheme on a 115-kV line.