Patent ID: 9316671
Filing Date: 2016-04-19
CPC Classification: G01R,H02H

Claim Text:
1. A method for sensing a fault in a protected unit included in a power system the protected unit being adapted to convey power from a first position in the protected unit to a second position, different from the first position, in the protected unit, or vice versa, wherein on a condition that a fault occurs in the protected unit at least one travelling wave is generated in the protected unit, wherein any distortion, attenuation and/or delay of the waveform of a wave due to propagation of the wave in the protected unit can be modeled by means of a propagation function, the method comprising: sensing at least one first current and at least one first voltage, respectively, in the first position; sensing at least one second current and at least one second voltage, respectively, in the second position; determining at least one first travelling wave current in the first position based on the at least one first current and the at least one first voltage; determining at least one second travelling wave current in the second position based on the at least one second current and the at least one second voltage; estimating at least one of the at least one first travelling wave current and the at least one second travelling wave current by applying the propagation function to the at least one second travelling wave current or to the at least one first travelling wave current, respectively; on a condition that the at least one first travelling wave current is estimated, comparing the estimated at least one first travelling wave current with the determined at least one first travelling wave current; on a condition that the at least one second travelling wave current is estimated, comparing the estimated at least one second travelling wave current with the determined at least one second travelling wave current; and based on the comparison or comparisons, determining whether there is a fault in the protected unit, on a condition that the at least one first travelling wave current is estimated: for each of the at least one first current and the at least one first voltage, determining a time when the respective current or voltage was sensed; and determining time information associated with the at least one first travelling wave current based on the time when the at least one first current and/or the at least one first voltage was sensed; on a condition that the at least one second travelling wave current is estimated: for each of the at least one second current and the at least one second voltage, determining a time when the respective current or voltage was sensed; determining time information associated with the at least one second travelling wave current based on the time when the at least one second current and/or the at least one second voltage was sensed, determining a time-shift function based on at least the determined time information and a propagation time period of a wave travelling from the first position to the second position, or vice versa; and prior to estimating at least one of the at least one first travelling wave current and the at least one second travelling wave current, applying the time-shift function to the propagation function so as to modify the propagation function, which subsequently is used in estimating at least one of the at least one first travelling wave current and the at least one second travelling wave current.