Electronic fault detector for variable frequency ac systems and circuit breaker incorporating same

• US 20030202303A1
• Filed: 04/30/2002
• Published: 10/30/2003
• Est. Priority Date: 04/30/2002
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Parker, Kevin Lynn
• Granted Patent: US 6,762,920 B2
• Time in Patent Office: Days
• US Class Current: 361/93.1
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 3/0935 the timing being determined by numerical means
• CPC Class Codes: H02H 3/44 responsive to the rate of change of electrical quantities

Abstract

A fault detector processes half cycles of current in variable frequency ac power systems by weighting half cycle magnitude values by the period of the half cycle. Time attenuated accumulations of the weighted half cycle peak values exceeding a first threshold for short delay protection, and of weighted positive differences between the peak values of successive half cycles and the preceding half cycles for a selected period of time after a peak value exceeds a second threshold for arc faults, generate trip signals when they reach specified levels.

Claims

1. A fault detector for a variable frequency ac electric power system comprising:

a current detector detecting variable frequency ac current flowing in the variable frequency ac electric power system; and

processing means for processing half cycles of the variable frequency ac current for indications of a fault.

2. The fault detector of claim 1, wherein the processing means comprises means processing half cycles of the variable frequency ac current for indications of an arc fault.

3. The fault detector of claim 1, wherein the processing means comprises means processing half cycles of the variable frequency ac current for indications of persistent overload current.

4. The fault detector of claim 1, wherein the processing means comprises measuring means measuring the magnitude and corresponding period of selected half cycles of the variable frequency ac current and signal generating means generating a fault signal as a function of the magnitude and corresponding period of the selected half cycles of the variable ac current.

5. The fault detector of claim 4, wherein the measuring means includes means detecting zero crossings of the variable frequency ac current for determining the corresponding period.

6. The fault detector of claim 4, wherein the selected half cycles of variable frequency ac current comprise successive half cycles of the variable frequency ac current.

7. The fault detector of claim 6, wherein the measuring means comprises means measuring the absolute magnitude and period of the successive half cycles of the variable frequency ac current.

8. The fault detector of claim 7, wherein the signal generating means comprises accumulating means generating a time attenuated accumulation of the absolute magnitude of the successive half cycles of the variable frequency ac current weighted by the period of the half-cycle and means generating a delayed overload current fault signal when the time attenuated accumulation reaches a predetermined short delay value.

9. The fault detector of claim 7, wherein the signal generating means comprises accumulating means generating a time attenuated accumulation of a difference between the absolute magnitude of the successive half cycles of the variable frequency ac current and the absolute magnitude of the immediately proceeding half-cycle of the variable frequency ac current, and means generating an arc fault signal when the time attenuated accumulation reaches a predetermined arc fault value.

10. The fault detector of claim 9, wherein the signal generating means includes threshold means for only accumulating differences between the absolute magnitude of successive half cycles of the variable frequency ac current following a half-cycle in which the absolute magnitude exceeds a selected threshold.

11. The fault detector of claim 10, wherein the threshold means only allows accumulation of differences in the absolute magnitude of successive half cycles of the variable frequency ac current for a selected time period after the selected threshold is exceeded.

12. A circuit breaker for a variable frequency ac power system, comprising:

separable contacts;

an operating mechanism opening the separable contacts in response to a trip signal; and

a fault detector comprising;

a current detector detecting variable frequency ac current flowing in the variable frequency ac electric power system; and

processing means for processing half cycles of the variable frequency ac current for indication of a fault and generating a trip signal in response to such a fault indication.

13. The circuit breaker of claim 12, wherein the processing means comprises measuring means measuring an absolute magnitude and corresponding period of successive half cycles of the variable frequency ac current and signal generating means comprising accumulating means generating a time attenuated accumulation of the differences between the absolute magnitude of successive half cycles of the variable frequency ac current and the absolute magnitude of the immediately preceding half cycle of the variable frequency ac current weighted by the period of the most recent half-cycle, and means generating an arc fault trip signal when the time attenuated accumulation reaches a predetermined arc fault value.

14. The circuit breaker of claim 13, wherein the signal generating means includes threshold means for only accumulating differences between the absolute magnitudes of successive half cycles of the variable frequency ac current following a half cycle in which the absolute magnitude exceeds a selected threshold.

15. The circuit breaker of claim 14, wherein the threshold means only permits accumulation of differences between the absolute magnitudes of successive high half cycles of the variable frequency ac current for a selected period after the selected threshold has been exceeded.

16. The circuit breaker of claim 12, wherein the processing means includes measuring means measuring the absolute magnitude and corresponding period of selected half cycles of the variable frequency ac current and signal generating means comprising accumulation means generating a time attenuated accumulation of the absolute magnitude of successive half cycles of the variable frequency ac current weighted by the period of the half-cycle, and means generating a short delay trip signal when the time attenuated accumulation reaches a predetermined short delay value.