Abstract: A method and a device for detecting faults and for protection of electrical networks, the electrical networks being fed from a transformer station through a first three-phase switching device with circuit breaker, a distribution network and feeders. A second three-phase switching device with circuit breaker is connected before the feeders. The circuit breaker of the second switching device, has parallel-coupled damping impedances and is connected in series between the first three-phase switching device and the feeders when a short circuit current is detected. At least one of the damping impedances has deviating properties compared to the others, so as to create a negative sequence current detectable in the electrical networks. The damping impedances are bypassed by the circuit breaker of the second switching device after a predetermined period of time.

Abstract: A method and a device for detecting faults and for protection of electrical networks, the electrical networks being fed from a transformer station through a first three-phase switching device with circuit breaker, a distribution network and feeders. A second three-phase switching device with circuit breaker is connected before the feeders. The circuit breaker of the second switching device, has parallel-coupled damping impedances and is connected in series between the first three-phase switching device and the feeders when a short circuit current is detected. At least one of the damping impedances has deviating properties compared to the others, so as to create a negative sequence current detectable in the electrical networks. The damping impedances are bypassed by the circuit breaker of the second switching device after a predetermined period of time.

Abstract: A method and a device for disconnection of faults in an electric network comprising a plurality of stations connected in a loop, comprising feeding the loop from at least two feeding points from a power source, earthing a neutral point of the electric network through an impedance, detecting earth faults in a directional earth fault protection in at least one first secondary substation provided with directional earth fault protection, disconnecting a detected earth fault by a load switching device in said at least one first secondary substation provided with directional earth fault protection, detecting fault currents arising from short circuits between two or more phases in an over-current protection of a second secondary substation, and opening said loop with a circuit breaker of said second secondary substation.

Abstract: A method, device and computer program product for determining at least one property of a current (Ip) running through the primary winding of a transformer operating in saturation using an unreliable detected current (Is) running through the secondary winding of the transformer. According to the invention a first reliable extreme point (EP1) of a cycle of the current in the secondary winding is detected and compared with an absolute time reference. Based on the comparison a first property of the current running through the primary winding in the form of the phase angle is then determined.

Abstract: A load compensation method for phase-to-ground loops in distance protection. A first reactive reach is estimated assuming zero fault resistance or with a positive sequence current. A second reactive reach is estimated with a zero sequence current. A third reactive reach is estimated with a negative sequence current. An import or export condition is estimated. A fourth reactive reach for import or export condition is estimated based on the first, second and third reactive reach. A fault impedance is estimated based on the estimated fourth reactive reach.

Abstract: The invention concerns a method and computer program product for determining the direction of fault in an electrical power system as well as to a fault handling device. In the fault handling device the voltage at a measurement node of the power system is measured, the phase (?PF) of this voltage (VPF) before a fault is stored, the phase (?F) of this voltage (VF) at the end of a time interval (TI) following directly after a detected fault is determined, a phase offset (?O) is determined as the difference between the phase (?PF) of the measured voltage (VPF) before the fault and the phase (?F) of the measured voltage (VF) at the end of the time interval (TI) and the phase (?F) of the measured voltage (VF) after the detection of the fault is adjusted with the phase offset (?O). Thereafter the adjusted measured voltage is used in determining the direction of fault in relation to the measurement node.

Abstract: A method, device and computer program product for determining at least one property of a current (Ip) running through the primary winding of a transformer operating in saturation using an unreliable detected current (Is) running through the secondary winding of the transformer. According to the invention a first reliable extreme point (EP1) of a cycle of the current in the secondary winding is detected and compared with an absolute time reference. Based on the comparison a first property of the current running through the primary winding in the form of the phase angle is then determined.

Abstract: The invention concerns a method and computer program product for determining the direction of fault in an electrical power system as well as to a fault handling device. In the fault handling device the voltage at a measurement node of the power system is measured, the phase (?PF) of this voltage (VPF) before a fault is stored, the phase (?F) of this voltage (VF) at the end of a time interval (TI) following directly after a detected fault is determined, a phase offset (?O) is determined as the difference between the phase (?PF) of the measured voltage (VPF) before the fault and the phase (?F) of the measured voltage (VF) at the end of the time interval (TI) and the phase (?F) of the measured voltage (VF) after the detection of the fault is adjusted with the phase offset (?O). Thereafter the adjusted measured voltage is used in determining the direction of fault in relation to the measurement node.

Abstract: A load compensation method for phase-to-ground loops in distance protection. A first reactive reach is estimated assuming zero fault resistance or with a positive sequence current. A second reactive reach is estimated with a zero sequence current. A third reactive reach is estimated with a negative sequence current. An import or export condition is estimated. A fourth reactive reach for import or export condition is estimated based on the first, second and third reactive reach. A fault impedance is estimated based on the estimated fourth reactive reach.