Protective relay devices

A protective relay device comprising

• a converter responsive to an electric quantity of an electric power system for producing an output proportional to said electric quantity, said converter including a time delay element,
• a detector responsive to said output from said converter, said detector including
• a first rectifier for producing a first DC voltage proportional to the output from said converter,
• a second rectifier for producing a second DC voltage smaller than said first DC voltage,
• a capacitor and a resistor for storing said second DC voltage and causing it to attenuate gradually,
• a source of constant DC voltage,
• means for producing a third DC voltage corresponding to the larger one of said first DC voltage and said constant voltage,
• a first level detector for producing an output when said first DC voltage exceeds a predetermined value,
• a first ON delay timer responsive to the output from said first level detector for producing an output with a time delay substantially equal to one cycle of said power system,
• a second level detector responsive to the difference between said second and third voltage for producing an output,
• a second ON delay timer which produces an output when the output from said first level detector persists for an interval slightly longer than one half cycle of said electric power system, and
• an output circuit which produces an output for operating the relay when the output from said first ON delay timer is applied provided that the second ON delay timer does not produce any output, and
• inhibit means for preventing misoperation of said detector due to an attenuating oscillation of said output caused by the transient phenomenon of said converter which occurs during the attenuation of said output.

In a phase comparison relay device wherein electric quantities at the opposite ends of a section of an electric power system are detected by detectors through converters each including a time delay element and compared by a phase detector at each end, the improvement wherein the detector at each end comprises

• first and second level detectors connected to respond to the output from the converter at one end of said section,
• first and second level setters responsive to different levels of the output from the converter at said one end for controlling said first and second level detectors respectively,
• said second level setter including
• a full wave rectifier for producing a first voltage proportional to the output from said converter at said one end,
• a capacitor and a resistor connected in parallel across said full wave rectifier,
• a source of constant DC voltage, and
• means for producing a second voltage which is proportional to the larger one of said first voltage and said constant DC voltage for producing a third voltage applied to said second level detector,
• a transmitter for transmitting the output from said first level detector at said one end to the other end of the section,
• a receiver for receiving the output of the first level detector at the other end of the section, and
• a phase detector for detecting the phase difference between the output between said second level detector at said one end and the output from said receiver for producing an output for operating said phase comparison relay device.