Method for detecting fault and current differential protection system thereof
View Patent ↗The present invention discloses a method for detecting a fault and a current differential protection system thereof. The method for detecting fault includes calculating fault component currents, calculating an operate current and a restraint current of all terminals, and adjusting an operate level by adapting an operate-restraint characteristic according to a fault component. The method has very small operating area for external faults, which makes the method very reliable even for the case with serious CT saturation. A very big operating area for internal faults makes the method very sensitive for internal faults even for a heavy load and high resistance fault.
1. A method for detecting fault of a protected circuit, comprising:
operating at least one current sensor so as to measure full component currents of two terminals, each full component current including a fault component current and a load component current;
calculating fault component currents for each terminal using the measured full component currents, each fault component current including a phase angle;
calculating a phase angle difference using the phase angle of each fault component current;
calculating an operate current and a restraint current based on the full component currents;
adjusting an operate level by adapting an operate-restraint characteristic according to the calculated phase angle difference; and
releasing a trip signal in response to the operate current exceeding the operate level.
2. The method according to the claim 1 , wherein said fault component currents include amplitudes and phase angles.
3. The method according to the claim 1 , wherein adjusting includes:
enhancing a sensitivity for an internal fault, and enhancing a reliability for an external fault.
4. The method according to claim 1 , wherein adjusting the operate-restraint characteristic comprises:
determining an internal fault or an external fault according to the phase angle difference.
5. The method according to claim 4 , wherein at least one of an internal or an external fault is determined by the phase angle difference being close to 0 degree or 180 degree.
6. The method according to claim 3 , wherein enhancing the sensitivity for the internal fault includes decreasing a threshold value required for the operation of the protection.
7. The method according to claim 3 , wherein enhancing the reliability for the external fault includes increasing a threshold value required for the operation of the protection so that unwanted operation is avoided.
8. A system for detecting fault of a protected circuit, comprising:
at least one current sensor configured to measure full component currents at all terminals; and
a fault detection unit configured to:
calculate fault component currents using the measured full component currents wherein each full component current includes a fault component current and a load component current,
calculate a phase angle difference using the phase angle of each fault component current,
calculate an operate current and a restraint current based on the full component currents,
adjust an operate level by adapting an operate-restraint characteristic according to the phase angle difference, and
release a trip signal in response to the operate current exceeding the adjusted operate level.
9. The system according to claim 8 , wherein the fault component currents include amplitudes and phase angles.
10. The system according to claim 8 , wherein the fault detection unit is further configured to enhance a sensitivity for an internal fault and enhance a reliability for an external fault.
11. The system according to claim 8 , wherein the fault detection unit is further configured to determine an internal fault or an external fault according to a phase angle difference.
12. The system according to claim 11 , wherein the fault detection unit is further configured to determine a fault to be an internal fault or an external fault by the phase angle difference being close to 0 degree or 180 degree.