Abstract: A solid state, reverse power flow detector and control circuit which samples the line voltage and current, once each cycle. The voltage sampling circuit includes a pulse generator providing a voltage pulse of short duration at a given time or phase angle in each cycle. The voltage signals are applied to an SCR through a gate operated by the current signals. With forward or no current the voltage signals do not reach the SCR. When current reverses the voltage signals are allowed to trigger the SCR. The SCR turns on a transistor energizing a relay, after a brief delay. The relay acts to set the regulator or other device in power reverse condition. When current again is forward the relay is deenergized and the device returned to the power forward condition.

Abstract: A circuit disposed between a power supply and a load for detecting the flow of an excess of power from the load back through the supply. The circuit is comprised of means for sensing the instantaneous current flowing between the power supply and the load, and means for sensing the instantaneous output voltage from the power supply. The circuit is further comprised of means responsive to the sensed instantaneous voltage and current for generating a signal that is indicative of instantaneous power flowing between the power supply and the load. Means is also provided for filtering out those components of the signal indicative of the instantaneous power which are at a frequency higher than the frequency of the AC current flowing between the power supply and the load to obtain a signal having a magnitude indicative of the average power flowing therebetween.

Abstract: The method of protecting power transmission lines is, accpording to the invention, based on a comparison between the actual quantities of current and/or voltage at the beginning of the protected section of a power transmission line and the same quantities of current and/or voltage calculated by means of current and voltage parameters at the end of the protected section providing there are no faults in this section. In apparatuses for realization of this method the voltage and current at the end of the protected section are multiplied in symmetrical components multipliers by respective coefficients of an equivalent four-terminal network substituting for the protected section and summed up. If there are no faults in this section, this calculated sum is equal to the respective electrical quantity at the beginning of the protected section.