Electricity: electrical systems and devices – Safety and protection of systems and devices – Arc suppression at switching point
Reexamination Certificate
2000-06-26
2003-09-16
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Arc suppression at switching point
Reexamination Certificate
active
06621668
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention deals with the field of electrical devices generally known as relays as well as the control circuit operative therewith. Such relay devices normally include a coil with relay contacts which are operable to close and open responsive to powering and de-powering, respectively, of the coil. This is an electro-mechanical operation which normally occurs in a matter of milliseconds. However, immediately after opening of the mechanical contacts, transient arcing currents can occur which tend to damage the surfaces of the mechanical contact by burning or allowing material to migrate from one contact to the other. Some minor arcing may also occur immediately after closing of the mechanical contacts if they bounce or wipe with respect to one another. Devices have been designed for the purposes of minimizing these transient arcing currents, however, the present invention provides a very rapidly responsive transient current suppressing system which preferably makes use of optical coupling and can be utilized with AC or DC relay coils.
2. Description of the Prior Art
Numerous prior art patents have been found for the purposes of relay control and the suppression of arcing in cross relay contacts such as shown in U.S. Pat. No. 2,637,769 patented May 5, 1953 to A. H. B. Walker and assigned to Westinghouse Brake and Signal Company Limited on a “Means For Suppressing Arcing at Contacts Breaking A Direct Current Inductive Circuit”; and U.S. Pat. No. 3,372,303 patented Mar. 5, 1968 to L. G. W. Knott and assigned to F. Devetta (Electronics) Limited on “A. C. Switch Contacts”; and U.S. Pat. No. 3,555,353 patented Jan. 12, 1971 to Charles F. Casson and assigned to American Machine & Foundry Company on a “Means Effecting Relay Contact Arc Suppression In Relay Controlled Alternating Load Circuits”; and U.S. Pat. No. 3,558,910 patented Jan. 26, 1971 to Robert G. Dale et al and assigned to Motorola, Inc. on “Relay Circuits Employing A Triac To Prevent Arcing”; and U.S. Pat. No. 3,639,808 patented Feb. 1, 1972 to Gerald R. Ritzow and assigned to Cutler-Hammer, Inc. on “Relay Contact Protecting Circuits”; and U.S. Pat. No. 3,783,305 patented Jan. 1, 1974 to Peter Lefferts and assigned to Heinemann Electric Company on an “Arc Elimination Circuit”; and U.S. Pat. No. 3,982,137 patented Sep. 21, 1976 to John K. Penrod and assigned to Power Management Corporation on an “Arc Suppressor Circuit”; and U.S. Pat. No. 4,025,820 patented May 24, 1977 to John K. Penrod and assigned to Power Management Corporation on a “Contactor Device Including Arc Suppression Means”; and U.S. Pat. No. 4,152,634 patented May 1, 1979 to John K. Penrod and assigned to Power Management Corporation on a “Power Contactor And Control Circuit; and U.S. Pat. No. 4,251,845 patented Feb. 17, 1981 to Harold E. Hancock and assigned to Power Management Corporation on an “Arc Suppressor Circuit”; and U.S. Pat. No. 4,296,449 patented Oct. 20, 1981 to Charles W. Eidhelberger and assigned to General Electric Company on a “Relay Switching Apparatus”; and U.S. Pat. No. 4,360,847 patented Nov. 23, 1982 to Milton D. Bloomer et al and assigned to General Electric Company on a “Diode Assisted Relay Contactor”; and U.S. Pat. No. 4,389,691 patented Jun. 21, 1983 to Harold E. Hancock and assigned to Power Management Corporation on a “Solid State Arc Suppression Device”; and U.S. Pat. No. 4,438,472 patented Mar. 20, 1984 to George K. Woodworth and assigned to IBM Corporation on an “Active Arc Suppression For Switching Ofg Direct Current Circuits”; and U.S. Pat. No. 4,525,762 patented Jun. 25, 1985 to Claude R. Norris on an “Arc Suppression Device and Method”; and U.S. Pat. No. 4,700,256 patented Oct. 13, 1987 to Edward K. Howell and assigned to General Electric Company on a “Solid State Current Limiting Circuit Interrupter”; and U.S. Pat. No. 4,745,511 patented May 17, 1988 to Michael M. Kugelman et al and assigned to The BF Goodrich Company on a “Means For Arc Suppression In Relay Contacts”; and U.S. Pat. No. 4,754,360 patented Jun. 28, 1988 to Ryosaku Nakada and assigned to Nipponkouatsudenki Kabushikikaisha on an “Arc Extinguishing Apparatus Having Sensing of Initial Arc”; and U.S. Pat. No. 4,760,483 patented Jul. 26, 1988 to Michael M. Kugelman et al and assigned to The B.F. Goodrich Company on a “Method For Arc Suppression In Relay Contacts”; and U.S. Pat. No. 4,772,809 patented Sep. 20, 1988 to Hirofumi Koga et al and assigned to Omron Tateisi Electronics Co. on a “Switching Circuit And A Relay Device Employed To Prevent Arcing”; and U.S. Pat. No. 4,816,818 patented Mar. 28, 1989 to Philip C. Roller and assigned to Truck-Lite Co., Inc. on a “Heavy Duty Lamp Flasher For Trucks, Trailers And The Like”; and U.S. Pat. No. 4,855,612 patented Aug. 8, 1989 to Hirofumi Koga et al and assigned to Omron Tateisi Electronics Co. on a “Switching Current And A Relay Device Employed Therein”; and U.S. Pat. No. 4,959,746 patented Sep. 25, 1990 to Chester C. Hongel and assigned to Electronic Specialty Corporation on a “Relay Contact Protective Circuit”; and U.S. Pat. No. 5,081,558 patented Jan. 14, 1992 to Leo M. Mahler and assigned to Northrop Corporation on “High Voltage DC Relays”; and U.S. Pat. No. 5,247,418 patented Sep. 21, 1993 to George C. Auge on an “Arc Suppressing Switch”; and U.S. Pat. No. 5,536,980 patented Jul. 16, 1996 to Keith W. Kawate et al and assigned to Texas Instruments Incorporated on a “High Voltage, High Current Switching Apparatus”.
SUMMARY OF THE INVENTION
The present invention takes advantage of the useful characteristics of a mechanical relay in combination with the advantages of a solid state relay by combining operation therebetween. In particular, the mechanical relay has contacts which can carry higher currents for longer periods of time without deterioration and without any need for dissipating heat. This characteristic is apparent in mechanical contacts since the current flowing therethrough generates a negligible amount of heat because of the very low voltage drop across these contacts when fully closed. The disadvantage, however, of mechanical contacts within the mechanical relay is that damaging arcing often occurs, immediately after opening, because at these times the contacts are very close to one another and arcing can easily occur. This arcing causes appreciable erosion of the contacts and deteriorates the contact surfaces and undesirably increases the voltage drop across such contacts, and can ultimately lead to contact failure. The deterioration of the mechanical contact surfaces can be attributable to the migration of material which can occur during the arcing, as well as the burning or charring of the contact surfaces.
A solid state switching mechanism has strikingly different operating characteristic advantages and disadvantages. In particular, a solid state switch such as a thyristor or transistor can open or close electrical circuits without any arcing whatsoever because of the nature of the solid state design. The problem with these devices however is they are severely stressed or can be permanently damaged by heat which builds up quickly when required to carry high currents. This unwanted heat is the result of the high voltage drop across these devices during operation thereof. Thus, very large and somewhat expensive heat sinks or other heat dissipation devices must be used in order to remove the heat when such solid state switches are required to carry fairly large currents for long periods of time.
The present invention takes advantage of the distinctively different characteristics of the mechanical relay and the solid state switch by using circuitry that connects the solid state switch in parallel to the relay contact. In the configuration of the present invention the solid state switch is operative to begin conducting, that is, becomes turned on just before the relay contacts close and become non-conductive a short time after the relay contacts have opened and remain non-conductive outside of these time periods. However, once the mechanical
Leja Ronald W.
Sperry, Zoda & Kane
Zytron Control Products, Inc.
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