Method and device for detection of a fault in a protected unit
View Patent ↗A method to facilitate fault detection in the protected unit after connection to the at least a portion of the power system. A current is sensed in the protected unit during a plurality of different time periods. Compliance of at least one of the sensed currents with a respective first current criteria is determined based on a first current threshold value. On a condition that there is determined that at least one of the sensed currents comply with the respective first current criteria, a fault in the protected unit is detected.
1. A method for use in fault detection in a protected unit included in a power system, the protected unit being adapted to convey power via at least one current path therein, wherein the protected unit is selectively disconnected from at least a portion of the rest of the power system and the protected unit is selectively connected to the at least a portion of the rest of the power system, the method being for facilitating detection of any fault in the protected unit after the protected unit has been connected to the at least a portion of the rest of the power system, the method comprising:
sensing, with a sensor, a current in the at least one current path in the protected unit at one end thereof during a plurality of different time periods, thereby obtaining a plurality of sensed currents;
determining, with a processing unit, compliance of at least one of the sensed currents with a respective first current criteria based on a first current threshold value, which first current criteria is a smaller than threshold criteria for a negative current and otherwise a larger than threshold criteria;
on a condition that there is determined that at least one of the sensed currents comply with the respective first current criteria, generating a signal with the processing unit indicating that there is a fault in the protected unit; and
on a condition that there is determined that none of the sensed currents comply with the respective first current criteria, generating a signal with the processing unit indicating that there is not a fault in the protected unit,
wherein on a condition that at least one of the generated signal or signals indicate that there is a fault, the protected unit is selectively disconnected from the at least a portion of the rest of the power system,
the sensed current in the at least one current path in the protected unit is sensed during at least three different respective time instants t 1 −t 0 , t 2 −t 0 , t 3 −t 0 , where t 0 is a time at which the protected unit is connected to the at least a portion of the rest of the power system after having been disconnected from the at least a portion of the rest of the power system, and t 3 >t 2 >t 1 >t 0 , thereby obtaining the plurality of sensed currents I(t 1 −t 0 ), I(t 2 −t 0 ), and I(t 3 −t 0 ), and
t 1 −t 0 is determined by a time for a fault current in the at least one current path in the protected unit to reach a maximum discharging or inrush current subsequent to the protected unit having been connected to the at least a portion of the rest of the power system after having been disconnected from the at least a portion of the rest of the power system, on a condition that the fault occurs at a terminal to which the protected unit is connected.
2. The method according to claim 1 , further comprising:
sensing a voltage of the at least one current path in the protected unit at one end thereof;
determining compliance of the sensed voltage with a voltage criteria based on a voltage threshold value;
on a condition that there is determined that the sensed voltage complies with the voltage criteria, generating a signal indicating that there is a fault in the protected unit.
3. The method according to claim 1 , wherein t 2 −t 0 is determined by a time for a fault current in the at least one current path in the protected unit to reach the first current threshold value on a condition that the fault occurs at a middle point of the at least one current path in the protected unit.
4. The method according to claim 1 , wherein t 3 −t 0 is determined by a time for a fault current in the at least one current path in the protected unit to reach the first current threshold value on a condition that the fault occurs at an end point of the at least one current path in the protected unit.
5. The method according to claim 1 , further comprising:
determining an absolute value of at least one of the sensed currents;
determining compliance of the absolute value with a second current criteria based on a second current threshold value; and
on a condition that there is determined that the absolute value complies with the second current criteria, generating a signal indicating that there is a fault in the protected unit.
6. The method according to claim 5 , wherein the signal indicating that there is a fault in the protected unit is generated if the absolute value exceeds the second current threshold value.
7. The method according to claim 1 , further comprising:
on a condition that at least one of the generated signal or signals indicates that there is a fault in the protected unit, generating a first derived signal indicating that there is a fault in the protected unit; and
on a condition that none of the generated signal or signals indicate that there is a fault in the protected unit, generating a first derived signal indicating that there is not a fault in the protected unit.
8. The method according to claim 7 , further comprising:
sensing a voltage of the at least one current path in the protected unit at one end thereof;
determining compliance of the sensed voltage with a voltage criteria based on a voltage threshold value;
on a condition that there is determined that the sensed voltage complies with the voltage criteria, generating a signal indicating that there is a fault in the protected unit; and
on a condition that both of said generated signal and the first derived signal indicate that there is a fault in the protected unit, generating a second derived signal indicating that there is a fault in the protected unit.
9. The method according to claim 1 , wherein a current in the at least one current path in the protected unit is sensed continuously during a time window;
wherein determining compliance of at least one of the sensed currents with a respective first current criteria based on a first current threshold value comprises:
determining at least one quotient of a difference between currents I(t>t 0 ) and I(t 0 ), where t denotes time, and a difference between t and t 0 ; and
comparing the determined at least one quotient during the time window with a current slope threshold value, the current slope threshold value constituting the first current threshold value.
10. The method according to claim 9 , wherein the time window is determined by a time for a fault current in the at least one current path in the protected unit to reach the first current threshold value on a condition that the fault occurs at an end point of the at least one current path in the protected unit.
11. A fault detection device for detection of a fault in a protected unit included in a power system, the protected unit being adapted to convey power via at least one current path therein, wherein the protected unit is selectively disconnected from at least a portion of the rest of the power system and the protected unit is selectively connected to the at least a portion of the rest of the power system, wherein the fault detection device is adapted to facilitate detection of any fault in the protected unit after the protected unit has been connected to the at least a portion of the rest of the power system, the fault detection device comprising:
a current sensor unit adapted to sense a current in the at least one current path in the protected unit at one end thereof during a plurality of different time periods, thereby obtaining a plurality of sensed currents;
a processing unit coupled to the current sensor unit and adapted to:
determine compliance of at least one of the sensed currents with a respective first current criteria based on a first current threshold value, which first current criteria is a smaller than threshold criteria for a negative current and otherwise larger than threshold criteria;
on a condition that there is determined that at least one of the sensed currents comply with the respective first current criteria, generate a signal indicating that there is a fault in the protected unit; and
on a condition that there is determined that none of the sensed currents comply with the respective first current criteria, generate a signal indicating that there is not a fault in the protected unit,
wherein on a condition that at least one of the generated signal or signals indicate that there is a fault, the protected unit is selectively disconnected from the at least a portion of the rest of the power system,
the sensed current in the at least one current path in the protected unit is sensed during at least three different respective time instants t 1 −t 0 , t 2 −t 0 , t 3 −t 0 , where t 0 is a time at which the protected unit is connected to the at least a portion of the rest of the power system after having been disconnected from the at least a portion of the rest of the power system, and t 3 >t 2 >t 1 >t 0 , thereby obtaining the plurality of at least three sensed currents I(t 1 −t 0 ), I(t 2 −t 0 ), and I(t 3 −t 0 ), and
t 1 −t 0 is determined by a time for a fault current in the at least one current path in the protected unit to reach a maximum discharging or inrush current subsequent to the protected unit having been connected to the at least a portion of the rest of the power system after having been disconnected from the at least a portion of the rest of the power system, on a condition that the fault occurs at a terminal to which the protected unit is connected.
12. The fault detection device according to claim 11 , wherein the processing unit is further adapted to:
determine the absolute value of at least one of the sensed currents;
determine compliance of the absolute value with a second current criteria based on a second current threshold value; and
on a condition that there is determined that absolute value complies with the second current criteria, generate a signal indicating that there is a fault in the protected unit.
13. The fault detection device according to claim 11 , further comprising:
a voltage sensor unit adapted to sense a voltage of the at least one current path in the protected unit at one end thereof;
wherein the voltage sensor unit is coupled to the processing unit; and
wherein the processing unit is further adapted to:
determine compliance of the sensed voltage with a voltage criteria based on a voltage threshold value; and
on a condition that there is determined that the sensed voltage complies with the voltage criteria, generate a signal indicating that there is a fault in the protected unit.
14. A power system including:
a protected unit adapted to convey power via at least one current path therein, wherein the protected unit is selectively disconnected from at least a portion of the rest of the power system and the protected unit is selectively connected to the at least a portion of the rest of the power system; and
a fault detection device according to claim 11 adapted to facilitate detection of any fault in the protected unit after the protected unit has been connected to the at least a portion of the rest of the power system.
15. The power system according to claim 14 , further including:
at least one DC circuit breaker adapted to selectively disconnect the protected unit from the at least a portion of the rest of the power system upon receipt of a disconnection signal and selectively connect the protected unit to the at least a portion of the rest of the power system upon receipt of a connection signal;
wherein the fault detection device is communicatively coupled to the at least one DC circuit breaker; and
wherein the processing unit of the fault detection device is adapted to, on a condition that at least one of the generated signals indicate that there is a fault in the protected unit, generate a disconnection signal and transmit the disconnection signal to the at least one DC circuit breaker, whereby the protected unit becomes disconnected from the at least a portion of the rest of the power system.
16. The power system according to claim 14 , wherein the power system comprises a High Voltage Direct Current, HVDC, power transmission system.
17. The power system according to claim 14 , wherein the protected unit comprises a power transmission line.
18. The power system according to claim 17 , wherein the power transmission line comprises a direct current, DC, power transmission line.
19. The power system according to claim 17 , wherein the power transmission line comprises an overhead line.
20. A computer program product adapted to be executed in a processing unit of a fault detection device in a power system, the computer program product comprising non-transitory computer-readable means carrying computer program code, the power system including a protected unit that is selectively isolated from at least a portion of the rest of the power system and the protected unit is selectively connected to the at least a portion of the rest of the power system after having been isolated from the at least a portion of the rest of the power system, wherein the fault detection device is adapted to facilitate detection of any fault in the protected unit after the protected unit has been connected to the at least a portion of the rest of the power system after having been isolated from the at least a portion of the rest of the power system, the fault detection device comprising a current sensor unit coupled to the processing unit and adapted to sense a current in the at least one current path in the protected unit at one end thereof at least once, the computer program code being configured to, when executed in the processing unit of the fault detection device:
cause the current sensor unit to sense a current in the at least one current path in the protected unit at one end thereof during a plurality of different time periods, thereby obtaining a plurality of sensed currents;
determine compliance of at least one of the sensed currents with a respective first current criteria based on a first current threshold value, which first current criteria is a smaller than threshold criteria for a negative current and otherwise a larger than threshold criteria;
on a condition that there is determined that at least one of the sensed currents comply with the respective first current criteria, generate a signal indicating that there is a fault in the protected unit; and
on a condition that there is determined that none of the sensed currents comply with the respective first current criteria, generate a signal indicating that there is not a fault in the protected unit,
wherein on a condition that at least one of the generated signal or signals indicate that there is a fault, the protected unit is selectively disconnected from the at least a portion of the rest of the power system,
the sensed current in the at least one current path in the protected unit is sensed during at least three different respective time instants t 1 −t 0 , t 2 −t 0 , t 3 −t 0 , where t 0 is a time at which the protected unit is connected to the at least a portion of the rest of the power system after having been disconnected from the at least a portion of the rest of the power system, and t 3 >t 2 >t 1 >t 0 , thereby obtaining the plurality of sensed currents I(t 1 −t 0 ), I(t 2 −t 0 ), and I(t 3 −t 0 ), and
t 1 −t 0 is determined by a time for a fault current in the at least one current path in the protected unit to reach a maximum discharging or inrush current subsequent to the protected unit having been connected to the at least a portion of the rest of the power system after having been disconnected from the at least a portion of the rest of the power system, on a condition that the fault occurs at a terminal to which the protected unit is connected.