Abstract: A method for detection of a sub-synchronous oscillation in a power system includes measuring a three-phase measurement signal of an electric system value, analyzing the measurement signal to detect an oscillation component of the measurement signal having an oscillation frequency lower than a system frequency of the power system, deciding whether the detected oscillation component at the oscillation frequency qualifies as a sub-synchronous oscillation, and disconnecting a generator from the power system that might be affected by the sub-synchronous oscillation. To detect sub-synchronous oscillations with low computational effort and good accuracy, an amplitude of each phase of the oscillation component is calculated and compared against a threshold, a sub-synchronous oscillation is detected upon exceeding the threshold during a given time delay, and a fault signal is generated upon detecting a sub-synchronous oscillation. A device having a processing unit is also provided.

Abstract: A method for detection of a sub-synchronous oscillation in a power system includes measuring a three-phase measurement signal of an electric system value, analyzing the measurement signal to detect an oscillation component of the measurement signal having an oscillation frequency lower than a system frequency of the power system, deciding whether the detected oscillation component at the oscillation frequency qualifies as a sub-synchronous oscillation, and disconnecting a generator from the power system that might be affected by the sub-synchronous oscillation. To detect sub-synchronous oscillations with low computational effort and good accuracy, an amplitude of each phase of the oscillation component is calculated and compared against a threshold, a sub-synchronous oscillation is detected upon exceeding the threshold during a given time delay, and a fault signal is generated upon detecting a sub-synchronous oscillation. A device having a processing unit is also provided.

Abstract: A differential protection method generates a fault signal which indicates that a fault has occurred at an electrical component of an energy supply network. Differential current values and stabilization values are formed from current measurement values at different measurement points of the component and the fault signal is generated if a measured value pair, formed from one of the differential current values and the respectively associated stabilization value, lies in a predetermined tripping range. The stabilization current values in a predetermined observation period are compared with the respective associated differential current values and, based on the comparison, a fault indicator is formed, which indicates whether the proportion of the differential current values or the proportion of the stabilization current values is greater. The generation of the fault signal is blocked if the fault indicator indicates a greater proportion of the stabilization current values.

Abstract: A method generates a fault signal that displays whether an internal transformer fault is present. According to the method, a differential current signal that indicates the difference between the primary current and the secondary current of the transformer, taking into consideration the conversion ratio of the transformer, is ascertained. A plurality of different criteria signals are generated using the differential current signal. At least two individual fuzzy matching functions are assigned to each criteria signal. The fuzzy matching functions are analyzed, thereby generating the fault signal.

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: 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 voltage stability within an electrical power system comprises the steps of establishing a dynamic power system stability margin based on an operating characteristic of the power system; indicating that the power system has become unstable when the dynamic power system stability margin falls below a predetermined value; and initiating dynamic load shedding and/or restoration depending on stability margin.

Abstract: A method of monitoring voltage stability within an electrical power system comprises the steps of establishing a dynamic power system stability margin based on an operating characteristic of the power system; indicating that the power system has become unstable when the dynamic power system stability margin falls below a predetermined value; and initiating dynamic load shedding and/or restoration depending on stability margin.