Abstract: A phase angle drift method for loss of mains/grid protection is disclosed. According to one aspect, an accumulated electrical phase angle drift derived from the difference between the current measured local frequency and the estimated frequency using historical data is compared to an angle threshold. An estimated grid frequency may be calculated based on the historical delay, and the window, over which the estimated frequency is calculated. An addition/subtraction of a phase angle offset value is calculated for a half cycle is performed when the frequency difference between the estimated frequency fnest and the measured frequency fn is greater or equal to a first determined value.

Abstract: A method of monitoring the grading margin between at least two time-current characteristics of Intelligent Electronic Devices (IEDA, IEDB) installed in an electrical power system, each Intelligent Electronic Device comprising a counting means, the grading margin comprising a safety margin set by a user, characterized in that it comprises, when a fault occurs which causes a fault current in the electrical power system, a step of providing a warning to the user when the safety margin is infringed upon.

Abstract: A method of predicting transient stability of a synchronous generator and a device for implementing such a method, the device comprising measurement means and calculation means for calculating an information which indicates, before it actually happens, whether the generator slip will be greater than zero or not at the critical phase angle.

Abstract: The invention concerns a method of impedance groundfault detection for differential protection of an overhead transmission line in a three-phase high voltage electric power transmission system which comprises many lines (1,12) and many protection relays (2,4), which comprises the following steps: 1) in prefault condition: —measuring the differential current (I); —measuring the phase voltage (II) at the relay location; —measuring the phase current (III) the relay location; —calculating the differential admittance (IV), with the following equation: (formula (V)). With (VI): the positive sequence impedance of the line-protected.

Abstract: A method of initiating the load shedding within an electrical power system comprising an electricity generator with a source impedance ZS and a load impedance ZL, characterized in that the method comprises: measuring the voltage VL at the terminal of the load impedance, calculating by means of a computer a voltage operative level VOP such that: VOP=K VC, where K is a number greater than 1 and VC is a critical voltage at the terminals of the load ZL at which the ratio ZL/ZC is equal to 1, VC depending on the difference ? between the phase angle ?L of the load impedance ZL and the phase angle ?S of the source impedance ZS, and comparing the voltage VL with the voltage operative level VOP so that the load shedding is initiated as soon as VL is equal to VOP.

Abstract: A relay for current differential protection of a transmission line, comprising: a first calculator of symmetrical sequence components of currents of each phase of the transmission line at local and remote ends of the transmission line; a second calculator of phase differences ?12 and ?012 between combinations currents i12 and i012 of the symmetrical sequence currents; a fuzzy inference system which outputs a variable y whose value is calculated according to the values of the phase differences ?12 and ?012; a third calculator which outputs a tripping signal for the control of a 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 at the local and remote ends of the protected transmission line.

Abstract: A method of monitoring the grading margin between at least two time-current characteristics of Intelligent Electronic Devices (IEDA, IEDB) installed in an electrical power system, each Intelligent Electronic Device comprising a counting means, the grading margin comprising a safety margin set by a user, characterized in that it comprises, when a fault occurs which causes a fault current in the electrical power system, a step of providing a warning to the user when the safety margin is infringed upon.