A method of free wave energy protection for a half-wavelength line based on a one-sided current includes: performing sampling and calculation on a current at protection measuring points to obtain variations in current sampling values; and activating a protective element to determine an occurrence time of a fault in a half-wavelength line. A free wave energy protection section includes a quick-action section, a basic section and a sensitive section, wherein the quick-action section, the basic section and the sensitive section serve as action criteria for performing protection with respect to the free wave energy of the half-wavelength line.

There is provided mechanisms for detecting a fault of a transmission line (20) in a power system (10) comprising at least one of an extreme weak system (10a) and an extreme strong system (10b). A method comprises obtaining travelling wave polarities from two terminals (21a, 21b) of the transmission line during occurrence of the fault, the travelling wave polarities being defined by two current polarities and two voltage polarities. The method comprises determining the obtained travelling wave polarities to be detectable and the obtained travelling wave polarities to be non-detectable. The method comprises detecting the fault to be internal based on the detectable travelling wave polarities and the non-detectable travelling wave polarities. There is also provided an arrangement configured to perform such a method.

The present disclosure relates to a method for protecting DC line impedance phase based on protection and control coordination, and an application scenario of the method for protecting is a three-terminal flexible DC transmission network. The method uses high controllability of a converter after a fault, injects a characteristic signal at a characteristic frequency, and calculates a phase angle of input impedance to determine a fault interval, which effectively improves protection performance, turns passive to active, and is not affected by nonlinearity of the converter. At the same time, compared with a full-bridge MMC, using a half-bridge MMC does not need to perform fault ride-through first when identifying a fault, and does not need to add additional equipment, it creates fault features and can reliably identify an fault interval; improves protection quickness and at the same time also has better economic benefits. It has selectivity, and an entire system may not be shut down due to failure of a single line.

A method and an apparatus for fault detection in a mixed configuration power transmission line including a plurality of sections arranged between one end of the transmission line and the other end of the transmission line and including at least one overhead line section and at least one cable section are disclosed. Based on a comparison travelling wave voltage or current time derivatives at the one end and the other end of the power transmission line with selected threshold values, it is determined if there is a fault occurring in at least one cable section of the power transmission line. Embodiments utilize amplification of travelling wave voltages and/or currents which may occur at junctions between a cable section and an adjacent overhead line section in determining if the fault occurs in a cable section of the power transmission line.

The invention provides a method and system for protection in response to a fault in a mixed line. The mixed line comprises two or more sections, with a first substation at a first end and a second substation at a second end. Every two consecutive sections of the mixed line are separated at a junction. The method is performed by an IED, and comprises obtaining one or more measurements of current at the first end, and one or more measurements of current at the second end. The method also comprises identifying a section of the two or more sections having the fault, by estimating a value of current for each junction and comparing the estimated value with the one or more measurements of current. In addition, the method comprises controlling a switching device based on the section identified with the fault.

The invention concerns a method of fault location in HVDC (High Voltage Direct Current) transmission lines, especially in mixed lines, where part of the line is overhead line and part is a cable line. The fault location is based on estimation arrival times of travelling waves induced by fault in transmission line that are propagating along the line from faulted point to the measurement point, which is located at one end of the transmission line.

A DC protection scheme for protecting a DC power transmission medium within a DC electrical power network. The scheme includes a protection device coupled to a DC power transmission medium, being operable to protect the power transmission medium from a fault; an apparatus to measure at least one electrical property of the power transmission medium; and a controller programmed to determine the direction of the electrical fault; determine whether the electrical fault is an internal or external fault; and operate the protection device to protect the DC power transmission medium if the determination of the direction of the electrical fault and/or the determination of whether the electrical fault is an internal or external fault meet a predefined criterion.

A DC distance protection controller for identifying a fault within a protection zone that extends between a first terminal and a set point along a DC power transmission conduit which lies between the first terminal and a second terminal within a DC electrical power network. The protection controller periodically obtains as respective sampled pairs a measured voltage value and a measured current value of the DC power transmission conduit; isolates a fault component voltage value and a fault component current value to define a respective corresponding isolated pair; calculates from each isolated pair a fault component operating voltage of the DC power transmission conduit at the set point; compare a given calculated fault component operating voltage with a historical voltage value; and identifies a fault within the protection zone when the given calculated fault component operating voltage is greater than the historical voltage value.

A DC distance protection scheme for protecting a DC power transmission medium within the DC electrical power network. The DC distance protection scheme includes a protection device that is coupled in use to a DC power transmission medium. The protection device is operable to protect the DC power transmission medium from an electrical fault. The DC distance protection scheme also includes a measurement apparatus to selectively measure the current and voltage of the DC power transmission medium. In addition the DC distance protection scheme also includes a controller that is programmed to calculate an operating voltage of the DC power transmission medium using the measured current and voltage; perform a transient comparison between the calculated operating voltage and the measured voltage; and operate the protection device to protect the DC power transmission medium if the transient comparison meets a predefined criterion.

The present disclosure relates to detection of faults in an electric power system. In one embodiment, a time-domain traveling wave directional subsystem is configured to receive a plurality of current traveling wave and a plurality of voltage traveling wave time-domain representations based on electrical conditions in the electric power delivery system. The plurality of current and voltage traveling wave time-domain representations may be compared to respective minimum thresholds. An integral may be generated based on a product of the plurality of current and voltage traveling wave time-domain representations when the current and voltage traveling wave time-domain representations exceed the minimum thresholds. A sign of the integral may reflect whether the fault is in the forward or reverse direction. A fault detector subsystem configured to declare the fault when the sign reflects that the fault is in the forward direction and the integral exceeds a security margin.