METHOD AND MEANS FOR DETECTING INCIPIENT CAPACITOR FAILURE

• US 3,657,602 A
• Filed: 04/05/1971
• Issued: 04/18/1972
• Est. Priority Date: 04/05/1971
• Status: Expired due to Term

• Current Assignee: Paul C. Boehm, Theodore R. Kennedy
• Original Assignee: Paul C. Boehm, Theodore R. Kennedy
• Inventors: Boehm, Paul C., Kennedy, Theodore R.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Fendelman, Harvey
• Application Number:
  US05/131,015
• Time in Patent Office: 379 Days
• Field of Search: 317/12A,12B,12R,53 324/54,6R,6C 340/253Y,248 307/129
• US Class Current: 361/15
• CPC Class Codes: H02H 7/16 for capacitors for synchronous capacitors H02H7/06

Abstract

Incipient failure of a capacitor operating as a part of an induction furnace circuit is detected by monitoring the capacitor to determine the presence of high-frequency signals generated by the capacitor as its dielectric material deteriorates. The lower limit of the frequencies of such signals is in the range from 50 to 200 kHz. The sensing apparatus for a 3 kHz induction heating circuit includes detector means for converting the generated signals exceeding about 150 kHz into a control signal whose level exceeds a predetermined value when the generated signals are representative of incipient deterioration of the dielectric. Indicator means responsive to the control signal is operated when the latter signal exceeds said predetermined value, and may disconnect power from the capacitor.

Claims

1. A method for detecting incipient deterioration of the capacitor in an A.C. power circuit including the steps of:

a. monitoring said capacitor to detect high-frequency signals produced by said capacitor; and

b. producing an indication when the level of said signals, whose lower frequency limit is in the range from 50 to 200 KHz, exceeds a predetermined value.

2. Sensing apparatus for detecting incipient deterioration of a capacitor in an A.C. power circuit including:

a. first circuit means to detect the presence of signals of a freqUency in excess of a predetermined value across said capacitor;

b. operable indicator means; and

c. second circuit means responsive to said signals for operating said indicator means when the level of said signals exceed a predetermined value.

3. Sensing apparatus according to claim 2 wherein the predetermined value of the frequency of said signals is in the range of 50 to 200 KHz.

4. Sensing apparatus according to claim 3 wherein said first circuit means includes a high-pass filter associated with said capacitor for effecting transmission of signals greater than the lower value of said range.

5. Sensing apparatus according to claim 4 wherein said first circuit means includes an isolation transformer whose primary is part of said high-pass filter, and a detector circuit associated with the secondary of said transformer for producing a rectified control signal whose level is functionally related to the signals passed by said filter.

6. Sensing apparatus according to claim 5 wherein said second circuit includes an active device responsive to said control signal for changing state when the level of said control signal exceeds a predetermined value.

7. Sensing apparatus according to claim 6 wherein the operation of said indicator means is responsive to a change in state of said active device.

8. Sensing apparatus according to claim 7 wherein said indicator means includes operable control means for controlling the application of power to said capacitor, operation of said indicator means causing operation of said control means whereby power is removed from said capacitor.

9. Sensing apparatus according to claim 6 wherein said second circuit includes latching means for maintaining said active device in its changed state independently of the level of said control signal once such level exceeds said predetermined value.

10. Sensing apparatus according to claim 9 wherein a reset circuit is provided for selectively returning said active device to its original state in the absence of a control signal whose level exceeds said predetermined value.