Method and apparatus for nondisruptively measuring line impedance at frequencies which are relatively close to the line frequency

摘要

Impedance of an energized electrical line which carries electrical current at a predetermined line frequency is nondistruptively measured at frequencies which are above and below the predetermined line frequency. A measurement current is generated at a measurement frequency between, for example, 10 Hz and 30 kHz for a 60 Hz line. The current generator is coupled to the energized electrical line by an isolating circuit which blocks only the predetermined line frequency and frequencies which differ from the predetermined line frequency by substantially less than the predetermined line frequency. For example, a notch filter may be used. A current sensor measures the line current in the energized line at the measurement frequency. A voltage sensor measures the line voltage in the energized electrical line at the measurement frequency. An analyzer determines impedance of the energized line at the measurement frequency. The measurement is repeated over a wide range of frequencies above and below the line frequency. Preferably, the current sensor and voltage sensor use the same current sensor to cancel errors. Improved nondisruptive line impedance measuring is thereby provided.