Method for sensing a fault in a power system based on travelling wave currents

A fault sensing system for a power system including a protected unit, the fault sensing system being adapted to sense a fault in the protected unit, wherein the protected unit is 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, the fault sensing system comprising:

• at least one current sensing adapted to sense at least one first current in the first position and at least one second current in the second position;
• at least one voltage sensing unit adapted to sense at least one first voltage in the first position and at least one second voltage in the second position;
• and
• at least one processing unit adapted to:
• determine 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;
• determine 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;
• model any distortion, attenuation and/or delay of the waveform of a wave due to propagation of the wave in the protected unit by means of a propagation function;
• estimate 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, compare 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, compare 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, determine whether there is a fault in the protected unit;
• the at least one processing unit being further adapted to
• 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, determine a time when the respective current or voltage was sensed;
• and
• determine 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, determine a time when the respective current or voltage was sensed;
• determine 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;
• determine 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, apply 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.

A computer program product adapted to be executed in a processing unit of a fault sensing system in a power system, the computer program product comprising non-transitory computer-readable means carrying computer program code, the power system comprising a protected unit, wherein the fault sensing system is adapted to sense a fault in the protected unit, and wherein the protected unit is 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, the fault sensing system further comprising at least one current sensing unit and at least one voltage sensing unit, wherein on a condition that a fault occurs in the protected unit at least one travelling wave is generated in the protected unit, wherein the processing unit is adapted to model any distortion, attenuation and/or delay of the waveform of a wave due to propagation of the wave in the protected unit by means of a propagation function;

• the computer program code being configured to, when executed in the processing unit of the fault sensing system, cause the at least one current sensing unit to sense at least one first current in the first position and at least one second current in the second position, and cause the at least one voltage sensing unit to sense at least one first voltage in the first position and at least one second voltage in the second position;
• the computer program code being further configured to, when executed in the processing unit of the fault sensing system:
• determine 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;
• determine 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;
• estimate 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, compare 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, compare 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, determine whether there is a fault in the protected unit,
• the computer program code being further configured to
• 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, determine a time when the respective current or voltage was sensed;
• and
• determine 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, determine a time when the respective current or voltage was sensed;
• determine 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,
• determine 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, apply 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.