System for detection of the phase of an electrical signal on an alternating circuit power line

An apparatus for measuring the phase angle of alternating voltage on a local power line relative to the phase of alternating voltage on a main power line which supplies power to the local power line, the phase of the alternating voltage on the main power line being defined as a reference phase end the phase of the alternating voltage on the local power line being defined as a local phase, comprising:

• a transmitter operably connected to the main power line for transmitting a first signal over said main power line;
• said transmitter including means for detecting the reference phase voltage and for generating said first signal, the first signal having a stable frequency and being modulated with a second signal derived from the reference phase voltage;
• a receiver operably connected to the local power line for receiving the first signal and its modulation;
• said receiver including means for detecting the local phase voltage of the local power line;
• said receiver including means for detecting the modulating second signal derived from the reference phase voltage from the received signal and measuring the phase angle of the local phase voltage relative to the second signal;
• and
• means on said receiver for displaying the measured phase angle.