MUs and IEDs are included. Each of the IEDs includes a signal control unit that derives the time difference between the sampling timings in the MUs on the basis of digital data from one end of a protection area and digital data from the other end of the protection area, controls the cycle of a sampling-timing control signal to eliminate this time difference, and outputs this controlled sampling-timing control signal to a merging unit corresponding to each computation unit. Each of the MUs includes a control-signal output circuit that generates a sampling signal synchronized with the sampling-timing control signal from the IEDs and outputs this sampling signal as a control signal, and a data output unit that converts an electrical input to digital data and outputs the digital data.

MUs and IEDs are included. Each of the IEDs includes a signal control unit that derives the time difference between the sampling timings in the MUs on the basis of digital data from one end of a protection area and digital data from the other end of the protection area, controls the cycle of a sampling-timing control signal to eliminate this time difference, and outputs this controlled sampling-timing control signal to a merging unit corresponding to each computation unit. Each of the MUs includes a control-signal output circuit that generates a sampling signal synchronized with the sampling-timing control signal from the IEDs and outputs this sampling signal as a control signal, and a data output unit that converts an electrical input to digital data and outputs the digital data.

A method in a power system which includes a protected unit, such as a transmission line, adapted to convey power from a first position in the protected unit to a second position in the protected unit, or vice versa, via a plurality of conductors. A first travelling wave differential current (ITWdiff) is determined based on a comparison between a determined first travelling wave current or a second travelling wave current in first and second positions and an estimation of the first travelling wave current or the second travelling wave current, respectively. The estimation is carried out using a propagation function which takes into account any distortion, attenuation and/or delay of the waveform of a wave due to propagation of the wave in the protected unit. A second or normalized travelling wave differential current (ITWdiff) is determined by means of, based on the propagation function, adjusting at least one of magnitude and phase of the first travelling wave differential current such that all modes attain equal or increasingly equal modal characteristics. The method may facilitate or enable mitigating or even eliminating any false differential current in elements of a travelling wave differential current vector which correspond to healthy conductors, caused by coupling effects between conductors.

A method in a power system which includes a protected unit, such as a transmission line, adapted to convey power from a first position in the protected unit to a second position in the protected unit, or vice versa, via a plurality of conductors. A first travelling wave differential current (ITWdiff) is determined based on a comparison between a determined first travelling wave current or a second travelling wave current in first and second positions and an estimation of the first travelling wave current or the second travelling wave current, respectively. The estimation is carried out using a propagation function which takes into account any distortion, attenuation and/or delay of the waveform of a wave due to propagation of the wave in the protected unit. A second or normalized travelling wave differential current (ITWdiff) is determined by means of, based on the propagation function, adjusting at least one of magnitude and phase of the first travelling wave differential current such that all modes attain equal or increasingly equal modal characteristics. The method may facilitate or enable mitigating or even eliminating any false differential current in elements of a travelling wave differential current vector which correspond to healthy conductors, caused by coupling effects between conductors.

In a differential protection method for monitoring a line of a power grid, current indicator measured values are measured at the ends of the line and are transmitted to an evaluation device. A differential current value is formed with current indicator measured values temporally allocated to one another. The time delay between local timers of the measuring devices is used for the temporal allocation of the current indicator measured values measured at different ends. A fault signal indicating a fault affecting the line is generated if the differential current value exceeds a predefined threshold value. A check is carried out using electrical measured quantities temporally allocated to one another and a line-specific parameter to determine whether the time delay information indicates the actual time delay between the respective local timers. A time error signal is generated if erroneous time delay information is detected.

Embodiments of the present invention disclose a current source converter differential protection method, including: sampling, by a relay protection device, secondary side currents of current transformers on two sides of a protected current source converter, to obtain incomer-side three-phase currents, and outgoer-side three-phase currents; rectifying the incomer-side three-phase currents and the outgoer-side three-phase currents, to obtain an incomer-side input current and an outgoer-side output current which are equivalent; converting the incomer-side input current and the outgoer-side output current according to a current ratio of the current transformers on the two sides, to acquire a transient differential current and a transient restraint current; acquiring a differential current and a restraint current according to the transient differential current and the transient restraint current; and achieving differential protection according to the differential current and the restraint current. The embodiments of the present invention further disclose a relay protection device correspondingly.

A fault monitoring method for a multi-port internal passive load-free probabilistic load flow (PLF) electric network is presented. Current transformers are installed on the conductors. Currents from the current transformers are transformed into voltages, and the voltages are then converted into pulses by a voltage-to-frequency conversion (VFC) circuit. The pulses are transmitted via optical fiber to a comparison module, and an algebraic sum of all pulse counts is calculated. It is stipulated that when an installation direction of the current transformer is the same as a direction of the port pointing to the PLF electric network, the pulse count is positive, and when the installation direction of the current transformer is opposite to the direction of the port pointing to the PLF electric network, the pulse count is negative. When the algebraic sum exceeds a threshold, it is determined that a fault has occurred within the PLF electric network.

A fault monitoring method for a multi-port internal passive load-free probabilistic load flow (PLF) electric network is presented. Current transformers are installed on the conductors. Currents from the current transformers are transformed into voltages, and the voltages are then converted into pulses by a voltage-to-frequency conversion (VFC) circuit. The pulses are transmitted via optical fiber to a comparison module, and an algebraic sum of all pulse counts is calculated. It is stipulated that when an installation direction of the current transformer is the same as a direction of the port pointing to the PLF electric network, the pulse count is positive, and when the installation direction of the current transformer is opposite to the direction of the port pointing to the PLF electric network, the pulse count is negative. When the algebraic sum exceeds a threshold, it is determined that a fault has occurred within the PLF electric network.