Fault protection for aircraft power systems

1. A method for protecting a power system, comprising:

tripping a generator in response to identifying a current on the generator that is greater than a first current threshold for a first time delay;

tripping the generator in response to identifying the current on the generator that is greater than a second current threshold for a second time delay, wherein the first current threshold is larger than the second current threshold and the first time delay is shorter than the second time delay;

selecting a shorter time delay for the first time delay in response to identifying a manual reset of a fault in the power system; and

otherwise selecting a longer time delay for the first time delay, wherein the longer time delay is longer than the shorter time delay.

2. The method of claim 1 , further comprising:

identifying a differential current condition on generator feeder lines providing power to the power system from the generator, wherein the differential current condition comprises a difference between a level of a first current at a first location on the generator feeder lines and a level of a second current at a second location on the generator feeder lines, wherein the first location is closer to the generator than the second location; and

tripping the generator in response to identifying the differential current condition on the generator feeder lines for more than a third time delay, wherein the third time delay is shorter than the first time delay.

3. The method of claim 2 , wherein identifying the differential current condition on the generator feeder lines comprises:

sensing the first current at a location of the generator; and

sensing the second current at an input to a power distribution system, wherein the power distribution system is configured to distribute the power from the generator to the power system.

4. The method of claim 2 further comprising:

clearing a fault at a location in the power system between a power distribution system and a load in response to identifying an undesired condition at the location in the power system between the power distribution system and the load for more than a fourth time delay, wherein the fourth time delay is shorter than the first time delay.

5. The method of claim 4 , wherein the undesired condition is selected from:

the differential current condition on load feeder lines providing power to the load; and a ground fault condition.

6. The method of claim 1 , wherein the power system is the power system on an aircraft and the generator is the generator on the aircraft.

7. The method of claim 1 , wherein the current on the generator that is greater than the first current threshold is an arc fault.

8. An apparatus comprising a power system protection controller configured to:

trip a generator in response to identifying a current on the generator that is greater than a first current threshold for a first time delay;

trip the generator in response to identifying the current on the generator that is greater than a second current threshold for a second time delay, wherein the first current threshold is larger than the second current threshold and the first time delay is shorter than the second time delay;

select a shorter time delay for the first time delay in response to identifying a manual reset of a fault in a power system; and

otherwise select a longer time delay for the second time delay, wherein the longer time delay is longer than the shorter time delay.

9. The apparatus of claim 8 , wherein the power system protection controller is further configured to:

identify a differential current condition on generator feeder lines providing power to a power system from the generator, wherein the differential current condition comprises a difference between a level of a first current at a first location on the generator feeder lines and a level of a second current at a second location on the generator feeder lines, wherein the first location is closer to the generator than the second location; and

trip the generator in response to identifying the differential current condition on the generator feeder lines for more than a third time delay, wherein the third time delay is shorter than the first time delay.

10. The apparatus of claim 9 further comprising:

a first current sensor located at a location of the generator and configured to sense the first current; and

a second current sensor located at an input to a power distribution system and configured to sense the second current, wherein the power distribution system is configured to distribute the power from the generator to the power system.

11. The apparatus of claim 9 , wherein the power system protection controller is further configured to clear a fault at a location in the power system between a power distribution system and a load in response to identifying an undesired condition at the location in the power system between the power distribution system and the load for more than a fourth time delay, wherein the fourth time delay is shorter than the first time delay.

12. The apparatus of claim 11 , wherein the undesired condition is selected from:

the differential current condition on load feeder lines providing power to the load; and

a ground fault condition.

13. The apparatus of claim 8 , wherein the generator is a generator on an aircraft and the apparatus is located on the aircraft.

14. The apparatus of claim 8 , wherein the current on the generator that is greater than the first current threshold is an arc fault.

15. A method for protecting a power system, comprising:

identifying a current on a generator that is greater than a first current threshold, wherein the generator provides power for the power system;

selecting a shorter time delay for a time delay in response to identifying a manual reset of a fault in the power system, otherwise selecting a longer time delay for the time delay, wherein the longer time delay is longer than the shorter time delay; and

tripping the generator in response to identifying the current on the generator that is greater than the first current threshold for more than the time delay.

16. The method of claim 15 further comprising:

tripping the generator in response to identifying the current on the generator that is greater than a second current threshold for longer than a second time delay, wherein the second current threshold is lower than the first current threshold and the second time delay is longer than the longer time delay.

17. The method of claim 15 further comprising:

identifying a differential current condition on generator feeder lines providing the power to the power system from the generator, wherein the differential current condition comprises a difference between a level of a first current at a first location on the generator feeder lines and a level of a second current at a second location on the generator feeder lines, wherein the first location is closer to the generator than the second location; and

tripping the generator in response to identifying the differential current condition on the generator feeder lines for more than a third time delay, wherein the third time delay is shorter than the shorter time delay.

18. The method of claim 15 wherein the power system is the power system on an aircraft, the generator is the generator on the aircraft, and the manual reset of the fault in the power system is initiated on a flight deck of the aircraft.

19. An apparatus comprising a power system protection controller configured to:

identify a current on a generator that is greater than a first current threshold, wherein the generator provides power for a power system;

select a shorter time delay for a time delay in response to identifying a manual reset of a fault in the power system, otherwise select a longer time delay for the time delay, wherein the longer time delay is longer than the shorter time delay; and

trip the generator in response to identifying the current on the generator that is greater than the first current threshold for more than the time delay.

20. The apparatus of claim 19 , wherein the power system protection controller is further configured to:

trip the generator in response to identifying the current on the generator that is greater than a second current threshold for longer than a second time delay, wherein the second current threshold is lower than the first current threshold and the second time delay is longer than the longer time delay.

21. The apparatus of claim 19 , wherein the power system protection controller is further configured to:

identify a differential current condition on generator feeder lines providing the power to the power system from the generator, wherein the differential current condition comprises a difference between a level of a first current at a first location on the generator feeder lines and a level of a second current at a second location on the generator feeder lines, wherein the first location is closer to the generator than the second location; and

trip the generator in response to identifying the differential current condition on the generator feeder lines for more than a third time delay, wherein the third time delay is shorter than the shorter time delay.

22. The method of claim 19 , wherein the power system is the power system on an aircraft, the generator is the generator on the aircraft, and the manual reset of the fault in the power system is initiated on a flight deck of the aircraft.