Abstract: An apparatus which indicates the sequence of a pair of alternating current input signals by determining the sense of a datum crossing in one input signal with respect to the polarity of the other input signal at the time of the datum crossing.

Abstract: An electrical coupling arrangement suitable for connecting protective relays to the primary current transducers in an alternating current power transmission system, comprising three winding arrangements flux linked so that an a.c. input current applied to one winding arrangement provides an a.c. output voltage substantially free of d.c. transients at a second winding arrangement, the third winding arrangement including a resistance which is variable and whose value determines the phase relationship between the output voltage and the input current.

Abstract: A voltage level detector which detects when a periodic waveform voltage exceeds a predetermined value for a predetermined time and upon detection produces an output, this output being cancelled, after a predetermined delay, if detection ceases. The drop off/pick up ratio of the detector may be reduced by providing feedback from the output.