Distance protection of electric power delivery systems using time domain and frequency domain
Distance protection of electric power delivery systems are disclosed herein where a fault within a zone of protection is detected using time-domain fault detection supervised by frequency-domain fault detection. The distance fault detection may be asserted when the real or imaginary parts of the time-domain operating and polarizing quantities are both positive or both negative and an angle between the frequency domain operating and polarizing quantities is within a predetermined range. Additional security may be provided using a level check, a sign consistency check, or a disturbance detector.
1. A system to determine a fault within a zone of protection of an electric power delivery system, comprising:
a signal processor to calculate a frequency-domain operating quantity, and a frequency-domain polarizing quantity;
a frequency-domain distance fault detector to:
compare the frequency-domain operating quantity and the frequency-domain polarizing quantity; and
when the frequency-domain operating quantity and frequency-domain polarizing quantity are within a predetermined range of each other, assert a frequency-domain fault detection signal;
a time-domain distance fault detector to:
calculate a time-domain operating quantity;
calculate a time-domain polarizing quantity;
determine a coincidence time that signs of the time-domain operating and polarizing quantities are the same;
when the coincidence time reaches a predetermined coincidence time threshold, assert a time-domain fault detection signal; and,
assert a distance fault detection signal when the frequency-domain fault detection signal is asserted and the time-domain fault detection signal is asserted; and,
a monitored equipment interface in communication with the electric power delivery system to effect a protective action in the electric power delivery system upon assertion of the distance fault detection signal.
2. The system of claim 1 , wherein the time-domain distance fault detector is further configured to:
calculate a real portion of the frequency-domain operating quantity;
calculate a real portion of the frequency-domain polarizing quantity;
determine a coincidence time that signs of the real portions of the frequency-domain operating and polarizing quantities are the same; and,
wherein when the coincidence time of the real portions of the frequency-domain operating and polarizing quantities are the same, assert the time-domain fault detection signal.
3. The system of claim 1 , wherein the time-domain distance fault detector is further configured to:
calculate an imaginary portion of the frequency-domain operating quantity;
calculate an imaginary portion of the frequency-domain polarizing quantity;
determine a coincidence time that signs of the imaginary portions of the frequency-domain operating and polarizing quantities are the same; and,
wherein when the coincidence time of the imaginary portions of the frequency-domain operating and polarizing quantities are the same or when the coincidence time of the real portions of the frequency-domain operating and polarizing quantities are the same, assert the time-domain fault detection signal.
4. The system of claim 1 , wherein the predetermined range of the frequency-domain distance fault detector comprises 90 degrees.
5. The system of claim 1 , wherein the predetermined coincidence time threshold comprises a time associated with a quarter of a power-system cycle.
6. The system of claim 1 , wherein the time-domain distance fault detector comprises an integrating timer to determine the coincidence time.
7. The system of claim 6 , wherein the frequency-domain operating quantity comprises a real portion of the frequency-domain operating quantity;
and further comprising a sign consistency check to:
determine when a sign of the real portion of the frequency-domain operating quantity coincides with a sign of a time-domain operating signal; and
signal the integrating timer to integrate down when the sign of the real portion of the frequency-domain operating quantity coincides with the sign of the time-domain operating quantity.
8. The system of claim 1 , wherein the frequency-domain operating quantity comprises a real portion of the frequency-domain operating quantity;
and further comprising a sign consistency check to:
assert a sign consistency operate signal when:
a sign of the real portion of the frequency-domain operating quantity coincides with a sign of a time-domain operating quantity; and
wherein the distance fault detection signal is only asserted when the sign consistency operate signal is asserted.
9. The system of claim 6 , wherein the time-domain distance fault detector further comprises a level check to:
determine when a magnitude of the time-domain operating quantity exceeds a predetermined minimum operating quantity threshold; and
signal the integrating timer to integrate down when the magnitude of the time-domain operating quantity exceeds the predetermined minimum operating signal threshold.
10. The system of claim 1 , wherein the time-domain distance fault detector further comprises a level check to:
assert a level check operate signal when:
a magnitude of the time-domain operating quantity exceeds a predetermined minimum operating quantity threshold; and
wherein the distance fault detection signal is only asserted when the level check operate signal is asserted.
11. The system of claim 1 , further comprising a disturbance detector to detect a power system disturbance and output a disturbance signal upon detection of the power system disturbance.
12. The system of claim 11 , wherein the time-domain distance fault detector comprises an integrating timer to determine the coincidence time, and upon assertion of the disturbance signal, the integrating timer resets.
13. The system of claim 1 , further comprising a frequency-domain timer with a predetermined frequency-domain security time, wherein the fault detection signal is only asserted upon assertion of the frequency-domain fault detection signal for a predetermined frequency-domain security time.
14. The system of claim 1 , wherein the coincidence time comprises a time that the signs of the time-domain operating quantities are the same and the frequency-domain fault detection signal is asserted.
15. A method to determine a fault within a zone of protection of an electric power delivery system, comprising:
an intelligent electronic device in communication with the electric power delivery system calculating a frequency-domain operating quantity;
calculating a frequency-domain polarizing quantity;
calculating a time-domain operating quantity;
calculating a time-domain polarizing quantity;
comparing the frequency-domain operating quantity and the frequency-domain polarizing quantity;
comparing signs of the time-domain operating quantity and the time-domain polarizing quantity;
asserting a distance fault detection signal when, for a predetermined coincidence time,
the frequency-domain operating quantity and frequency-domain polarizing quantity are within a predetermined range; and,
the time-domain operating quantity and the time-domain polarizing quantity have the same sign; and,
effecting a protective action in the electric power delivery system upon assertion of the fault detection signal.
16. The method of claim 15 , wherein the predetermined coincidence time comprises a time associated with a quarter of a power-system cycle.
17. The method of claim 15 , wherein the step of asserting the fault detection signal comprises asserting when a real portion of the frequency-domain operating quantity and a real portion of the frequency-domain polarizing quantity are within the predetermined range.
18. The method of claim 15 , wherein the step of asserting the fault detection signal comprises asserting when an imaginary portion of the frequency-domain operating quantity and an imaginary portion of the frequency-domain polarizing quantity are within the predetermined range.
19. The method of claim 15 , further comprising:
determining when a magnitude of the time-domain operating quantity exceeds a predetermined minimum operating signal threshold; and
integrating the coincidence time down when the magnitude of the time-domain operating quantity exceeds the predetermined minimum operating quantity threshold.
20. The method of claim 15 further comprising:
calculating a real portion of the frequency-domain operating quantity;
comparing a sign of the real portion of the frequency-domain operating quantity with a sign of the time-domain operating quantity; and
asserting the distance fault detection signal only when the sign of the real portion of the frequency-domain operating quantity coincides with the sign of the time-domain operating quantity.
21. The method of claim 15 , further comprising:
detecting a disturbance on the electric power delivery system; and
upon detecting the disturbance, the distance fault detection signal is not asserted.