Digitally controlled circuit interrupter with improved automatic selection of sampling interval for 50 Hz and 60 Hz power systems

• US 5,559,719 A
• Filed: 05/26/1994
• Issued: 09/24/1996
• Est. Priority Date: 05/26/1994
• Status: Expired due to Term

• Current Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Johnson, Richard A., Engel, Joseph C., Saletta, Gary F., Shimp, Alan B.
• Primary Examiner(s): Trammell, James P.
• Assistant Examiner(s): VO, HIEN XUAN
• Application Number:
  US08/249,829
• Time in Patent Office: 852 Days
• Field of Search: 364/483, 364/492, 324/520, 324/76.11, 361/87, 361/85, 361/78
• US Class Current: 700/293
• CPC Class Codes: G01R 23/10 by converting frequency into a train of pulses, which are then counted , i.e. converting the signal into a square wave
• CPC Class Codes: H02H 3/006 Calibration or setting of parameters

Abstract

A circuit interrupter with a digital trip unit automatically sets the sampling interval appropriate for the 50 Hz or 60 Hz distribution system to which the interrupter is connected. In order to avoid falsely shifting the interval in response to distorted currents, the trip unit only changes the interval if the number of zero crossings of the current within a fixed number of samples is within two zero crossings of the number of zero crossings for an undistorted current of the other frequency for two consecutive time periods in which the fixed number of samples are taken. Furthermore, changes in the interval are only written into an EEPROM for use on power-up a fixed number of times to preclude disabling the EEPROM. In one embodiment, a 2 pole filter is utilized in the zero crossing counting circuit to eliminate false counts from noise originating in a chopper used in the trip unit power supply. In another embodiment, the zero crossing counting circuit is disabled unless external dc power is available for the trip unit which idles the chopper.

Claims

1. Electrical apparatus for connecting a load to either of a 50 Hz power source and a 60 Hz power source, said apparatus comprising:

separable contacts selectively connecting said load to a selected one of said 50 Hz power source and said 60 Hz power source when closed and disconnecting the load from the selected power source when open;

sensing means sensing current flowing through said separable contacts to the load when said contacts are closed;

digital control means including digitizing means digitally sampling said current sensed by said sensing means at selectable time intervals to generate digital current signals, and means responsive to predetermined values of said digital current signals to generate a trip signal;

means setting said selectable interval either to a first interval for a 50 Hz source or a second interval for a 60 Hz source and comprising zero crossing counting means generating a count of zero crossings of said current and means changing said selectable interval from said first interval to said second interval when said count during a first predetermined time period is within a first preselected number of zero crossings of a first number of zero crossings produced by an undistorted 60 Hz source during said first predetermined time period, and changing said selectable interval from said second interval to said first interval when said count within a second predetermined time period is within a second preselected number of zero crossings of the number of zero crossing produced by an undistorted 50 Hz source during said second predetermined time period;

means responsive to a trip signal to open said contacts; and

wherein said means changing said selectable interval only changes said interval from said first interval to said second interval when said count is within said first preselected number of zero crossings of said first count during a designated number of said first predetermined time periods, and only changes said interval from said second interval to said first interval when said count is within said second preselected number of zero crossings of said second count during said designated number of said second predetermined time periods, wherein said means setting said selectable interval includes an EEPROM in which the interval selectable is written for use by said digitizing means upon powering up of said digital control means and means blocking said means changing said selectable interval from further writing of said selected interval into said EEPROM after said selectable interval has been written into said EEPROM a predetermined number of times.

2. Electrical apparatus for connecting a load to either of a 50 Hz power source and a 60 Hz power source, said apparatus comprising:

separable contacts selectively connecting said load to a selected one of said 50 Hz power source and said 60 Hz power source when closed and disconnecting the load from the selected power source when open;

sensing means sensing current flowing through said separable contacts to the load when said contacts are closed;

digital control means including digitizing means digitally sampling said current sensed by said sensing means at selectable time intervals to generate digital current signals, and means responsive to predetermined values of said digital current signals to generate a trip signal;

means setting said selectable interval either to a first interval for a 50 Hz source or a second interval for a 60 Hz source and comprising zero crossing counting means generating a count of zero crossings of said current and means changing said selectable interval from said first interval to said second interval when said count during a first predetermined time period is within a first preselected number of zero crossings of a first number of zero crossings produced by an undistorted 60 Hz source during said first predetermined time period, and changing said selectable interval from said second interval to said first interval when said count within a second predetermined time period is within a second preselected number of zero crossings of the number of zero crossing produced by an undistorted 50 Hz source during said second predetermined time period;

means responsive to a trip signal to open said contacts; and

wherein said digital control means includes chopper means regulating dc power provided to said digital control means and which generates noise affecting said zero crossing counting means generating a count of zero crossings of said current, and filter means connected to said zero crossing counting means to filter out said noise generated by said chopper means.

3. The apparatus of claim 2 wherein said filter is at least a two pole filter tuned to filter said noise generated by said chopper.

4. The apparatus of claim 3 wherein said means setting said selectable time interval is disabled by disabling said means generating said count of zero crossings of said current.

5. Electrical apparatus for connecting a load to either of a 50 Hz power source and a 60 Hz power source, said apparatus comprising:

separable contacts selectively connecting said load to a selected one of said 50 Hz power source and said 60 Hz power source when closed and disconnecting the load from the selected power source when open;

sensing means sensing current flowing through said separable contacts to the load when said contacts are closed;

digital control means including digitizing means digitally sampling said current sensed by said sensing means at selectable time intervals to generate digital current signals, and means responsive to predetermined values of said digital current signals to generate a trip signal;

means setting said selectable interval either to a first interval for a 50 Hz source or a second interval for a 60 Hz source and comprising zero crossing counting means generating a count of zero crossings of said current and means changing said selectable interval from said first interval to said second interval when said count during a first predetermined time period is within a first preselected number of zero crossings of a first number of zero crossings produced by an undistorted 60 Hz source during said first predetermined time period, and changing said selectable interval from said second interval to said first interval when said count within a second predetermined time period is within a second preselected number of zero crossings of the number of zero crossing produced by an undistorted 50 Hz source during said second predetermined time period;

means responsive to a trip signal to open said contacts; and

wherein said digital control means includes means supplying dc control power to said digital control means from an auxiliary source, and internal power supply means generating alternative dc control power from said current and including chopper means regulating said alternative dc control power and generating noise which affects said means generating a count of zero crossings of said current, said digital control means further including disabling means responsive to absence of control power from said auxiliary source for disabling said means setting said selectable time interval.

6. Electrical apparatus for controlling electrical power in a load, where the electrical power comprises an electrical current with an actual frequency which may be either of two values, comprising:

zero crossing sensing means for sensing the zero crossings within limits of said electrical current;

frequency determining means for initially generating an estimated frequency substantially equal to one of said two values;

comparison means interconnected with said zero crossing sensing means and said frequency determining means for comparing an interval related to said estimated frequency with the number of said zero crossings and indicating;

that said actual frequency is substantially equal to said estimated frequency if the number of said zero crossing within limits when compared with said interval is equal to a first number,

that said actual frequency is substantially lower than said estimated frequency if the number of said zero crossings within limits when compared with said interval is equal to a second number,

that said actual frequency is substantially higher than said estimated frequency if the number of said zero crossings within limits when compared with said interval is equal to a third number,

said comparison means resetting said frequency determining means to said lower of said two values upon the occurrence of said second number,

said comparison means resetting said frequency determining means to said higher of said two values upon the occurrence of said third number,

the occurrence of said first number confirming that said estimated frequency is substantially said actual frequency;

activity sensing means for sensing activity in a component of said electrical power; and

actuating means interconnected with said frequency determining means and said activity sensing means for causing an action as a function of the occurrence of a predetermined level of said activity and the presence of said actual frequency.

7. A circuit interrupter for interrupting electrical current which has an actual frequency which may be either of two values,

zero crossing sensing means for sensing the zero crossings within limits of said electrical current;

frequency determining means for initially generating and estimated frequency substantially equal to one of said two values;

comparison means interconnected with said zero crossing sensing means and said frequency determining means for comparing an interval related to said estimated frequency with the number of said zero crossings and indicating;

that said actual frequency is substantially equal to said estimated frequency if the number of said zero crossings within limits when compared with said interval is equal to a first number,

that said actual frequency is substantially lower than said estimated frequency if the number of said zero crossings within limits when compared with said interval is equal to a second number,

that said actual frequency is substantially higher than said estimated frequency if the number of said zero crossings within limits when compared with said interval is equal to a third number,

said comparison means resetting said frequency determining means to said lower of said two values upon the occurrence of said second number,

said comparison means resetting said frequency determining means to said higher of said two values upon the occurrence of said third number,

the occurrence of said first number confirming that said estimated frequency is substantially said actual frequency;

current sensing means for sensing the occurrence of a predetermined level of said current; and

separable main contact means interconnected with said frequency determining means and said current sensing means for opening as a function of the occurrence of said predetermined level and the presence of said actual frequency.

8. The combination as claimed in claim 7, wherein said lower of said two values is 50 Hz.

9. The combination as claimed in claim 7, wherein said higher of said two values is 60 Hz.

10. The combination as claimed in claim 7, wherein said first number is substantially 77.75 within limits, said second number is in a range between 63 and 66, and said third number is in a range between 92 and 95.