Fuzzy interference relay and method for current differential protection of a transmission line

A relay for current differential protection of at least one transmission line, comprising at least:

• a first calculator of symmetrical sequence currents, which include zero sequence currents i0, positive sequence currents i1 and negative sequence currents i2, of currents of each phase of the transmission line at local and remote ends of the protected transmission line;
• a second calculator of phase differences φ12 and φ012 between combinations currents i12 and i012 of the symmetrical sequence currents i0, i1 and i2 of each ends of the transmission line;
• a fuzzy inference system which outputs a variable y whose value is calculated according to the values of the phase differences φ12 and φ012;
• a third calculator which outputs a tripping signal for the control of at least one circuit breaker arranged on the transmission line and associated with the relay, the value of the tripping signal being calculated according to the values of the variable y and the values of the currents of each phase of the transmission line at the local and remote ends of the protected transmission line.