Abstract:
A relay is provided for a transfer mechanism which transfers power between a utility source and a stand-by electrical generator. The relay incorporates contacts formed from two distinct materials. A backing portion of each contact is formed from copper and a contacting portion is deposited on the backing portion. The contacting portion is formed from tungsten. The arrangement of the contact minimizes the potential for failure of the transfer mechanism when the transfer mechanism is exposed to significant current and/or heating during operation thereof.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. Ser. No. 09/377,722, filed Aug. 19, 1999 now U.S. Pat. No. 6,181,028, and entitled “Transfer Mechanism For Transferring Power Between a Utility Source and a Stand-by Generator.” 
    
    
     FIELD OF THE INVENTION 
     This invention relates to stand-by generators, in particular, to a relay for a transfer mechanism which transfers the supply of power between a utility source and a stand-by generator. 
     BACKGROUND OF THE INVENTION 
     As is known, virtually all facilities which utilize electric power receive such power from a utility company. Typically, such utility companies have an excellent record of providing uninterrupted or infrequently interrupted power at proper voltage levels and line frequency. However, due to the increasing demands for electricity, power outages have become more frequent. While such outages usually last for a only a short duration, an extended power outage may cause more than simple aggravation for customers of the utility company. By way of example, for a residential customer, any power outage renders a home owner&#39;s sump pump inoperable. If a power outage occurs during a rain storm, it is quite possible that the failure of the sump pump to operate will result in the flooding of a home owner&#39;s basement. 
     In order to overcome these occasional disruptions in service, various customers, including home owners, have equipped their facilities with stand-by power systems. These stand-by power systems include internal combustion engines which drive electrical generators. If the commercial power from the utility company fails, the internal combustion engine is automatically started causing the electrical generator to generate power. When the power generated by the generator reaches the voltage and frequency desired by the customer, a manually operated transfer switch transfers the load imposed by the customer from the commercial power lines to the generator. 
     Typically, the transfer mechanism incorporates a switch which isolates the power supplied by the utility company and the generator. In a residential application, a home owner manually flips a switch between the utility source and the generator in order to provide power to the electrical system of the home. However, due to a potential time delay before the home owner can flip the switch, a significant amount of damage may be sustained by a home owner before power is supplied to the electrical system of the home. For example, an extended power outage may result in foodstuffs spoiling within a refrigerator or melting within a freezer. Therefore, it is highly desirable to provide a transfer mechanism which automatically transfers power from the utility company to the generator whenever the generator is activated. 
     Further, prior art transfer mechanisms require a home owner to transfer the entire electrical system of the home onto the generator. Such an arrangement does not allow a home owner the ability to decide which circuits of a home&#39;s electrical system to be powered. As such, it is also desirable to provide a transfer mechanism which allows various branch circuits of a home to be brought on line separately, rather than at once, to allow for loads with large starting requirements to be brought up to speed before bringing the other circuit branches of the home on line thereby insuring that adequate power is provided by the generator to start such loads. 
     It can be appreciated that, in operation, in order to transfer power between the utility company and the generator, significant voltage and current flow through the transfer mechanism during such transfer. As such, the components of the transfer mechanism must be able to perform in such an environment without failure. As is known, the transfer mechanism must operate when exposed to high current and/or heat. Therefore, it is highly desirable to provide components for a transfer mechanism which minimize the potential for failure of the transfer mechanism when the transfer mechanism is exposed to significant current and/or heat during operation thereof. 
     Therefore, it is a primary object and feature of the present invention to provide for a transfer mechanism which transfers the power supplied to a load between a utility source and a stand-by generator. 
     It is a further object and feature of the present invention to provide a relay for a transfer mechanism which automatically transfers the power supplied to a load from the utility source to the generator in response to a power outage. 
     It is a still further object and feature of the present invention to provide a relay for a transfer mechanism which transfers the power supplied to a load between a utility source and a generator such that the transfer mechanism is less prone to failure than prior transfer mechanisms. 
     It s a still further object and feature of the present invention to provide a relay for a transfer mechanism which is reliable and inexpensive to manufacture. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a relay is provided relaying electrical power between first and second terminals thereof. The relay includes a stationary contact having a backing portion operatively connected to the first terminal and formed from a first material. The stationary contact also includes a contacting portion deposited on the backing portion and formed from a second material. A movable arm has a first end operatively connected to the second terminal and a second opposite end. The relay includes a movable contact having a backing portion operatively connected to the second end of the movable arm and formed from the first material. A contacting portion is deposited on the backing portion of the movable contact and is formed from the second material. A coil is operatively connected to the movable arm such that the movable arm is movable between a first contacting position wherein the contacting portion of the movable contact engages the contacting portion of the stationary contact and a second non-contacting position wherein the contacting portion of the movable contact is disengaged from the contacting portion of the stationary contact in response to an electrical charge on the coil. 
     A biasing structure is provided for urging the movable arm towards the non-contacting position. It is contemplated that first material be copper and the second material be tungsten. The first surface of the backing portion of the stationary contact has a first diameter and the second surface of the backing portion of the stationary contact has a second diameter which is greater than the first diameter. In addition, the first surface of the contacting portion of the movable contact has a first diameter and the second surface of the contacting portion of the movable contact has a second diameter which is greater than the first diameter. The first surface of the contacting portion of the movable contact is generally arcuate in shape and terminates at a crown. 
     In accordance with a still further aspect of the present invention, a contact for a relay is provided. The relay relays electrical power between first and second terminals thereof. The contact includes a backing portion formed from copper and a contacting portion deposited on the backing portion. The contacting portion is formed from tungsten. 
     The contacting portion of the contact includes a first surface and a second surface which engages the backing portion of the contact. The first and second surfaces of the contacting portion are spaced from each other by an outer edge. The first surface of the contacting portion has a first diameter and the second surface of the contacting portion has a second diameter which is greater than the first diameter. The first surface of the contacting portion is generally arcuate in shape and terminates at a crown. The backing portion includes a first surface which engages the contacting portion and a second surface spaced from the first surface of the backing portion by an outer edge. A mounting head depends from the second surface of the backing portion to facilitate mounting of the contact to an element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment. 
     In the drawings: 
     FIG. 1 is an isometric view of an enclosure for housing a transfer mechanism in accordance with the present invention; 
     FIG. 2 is a front elevational view, with its cover removed, of the enclosure of FIG. 1; 
     FIG. 3 is a wiring diagram of the transfer mechanism of the present invention; 
     FIG. 4 is a schematic diagram of a first embodiment of the transfer mechanism of the present invention; 
     FIG. 5 is a schematic view of a second embodiment of the transfer mechanism of the present invention; 
     FIG. 6 is a side elevational view of a relay for the transfer mechanism of FIGS. 1-5; 
     FIG. 7 is an enlarged, side elevational view taken along line  7 — 7  of FIG. 6; 
     FIG. 8 is a cross-sectional view of a stationary contact for use in connection with the relay of FIG. 6; 
     FIG. 9 is a cross-sectional view of a movable contact for use in connection with the relay of FIG. 6; and 
     FIG. 10 is a cross-sectional view of an alternate embodiment of a movable contact for use with the relay of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 2 and 3, a transfer mechanism in accordance with the present invention is generally designated by the reference numeral  10 . It is contemplated that transfer mechanism  10  be mounted within a housing  12 , FIGS.  1  and  2 . Housing  12  includes a cabinet  14 . Cabinet  14  defines a pair of sidewalls  16  and  18 , a top wall  20  extending between upper ends of sidewalls  16  and  18 , a bottom wall (not shown) extending between and interconnecting the lower ends of sidewalls  16  and  18 , and a rear panel  22 . Upper and lower mounting flanges  24  and  26  project from opposite ends of rear panel  22  of cabinet  14  and include apertures  28  therein for allowing cabinet  14  to be mounted on a wall within the interior of a building via screws or the like. 
     Housing  12  further includes a cover  30  defined by a pair of sidewalls  32 , a top wall  34  extending between the upper ends of sidewalls  32 , a bottom wall (not shown) extending between and interconnecting the lower ends of sidewalls  32 , and a front panel  36 . Front panel  36  of cover  30  includes an opening  38  therein so as to allow for a plurality of circuit breakers to project therethrough, as hereinafter described. Cover  30  may be positioned on cabinet  14  to limit access to transfer mechanism  10  contained therein. 
     Referring to FIG. 4, transfer mechanism  10  is interposed between a utility source  42  and a stand-by generator  44 . As is conventional, utility source  42  is interconnected to ground  46  through line  48  and supplies ±120 volts across lines  50  and  52 . Lines  50  and  52  are connected to a main circuit breaker  54  within a main distribution panel located in the interior of a building. As is conventional, two bus bars  56  and  58  are connected to main circuit breaker  54 . A plurality of single pole circuit breakers  60  and  62  are interconnected to bus bar  58 . Similarly, a plurality of single pole circuit breakers  64  and  66  are interconnected to bus bar  56 . Circuit breakers  60 ,  62 ,  64  and  66  are operatively connected to corresponding individual branch circuits within the building which requires 120 volt service, in a manner hereinafter described. A double pole circuit breaker  68  may be attached to both bus bars  56  and  58 . Circuit breaker  68  is operatively connected to a corresponding individual branch circuit which requires 240 volt service, in a manner hereinafter described. 
     As best seen in FIGS. 3-4, circuit breakers  60  and  64  are interconnected to normally closed contacts  70  and  76 , respectively, of a first double pole, double throw power relay  77  through corresponding lines  78  and  84 , respectively. Circuit breakers  62  and  66  are interconnected to normally closed contacts  72  and  74 , respectively, of a second double pole, double throw power relay  79  through lines  80  and  82 , respectively. Double pole circuit breaker  68  is interconnected to normally closed contacts  88  and  90  of a third double pole, double throw power relay  92  through corresponding lines  94  and  96 , respectively. Referring to FIGS. 2 and 3, it is contemplated to mount a terminal block  86  to rear panel  22  of cabinet  14  in order to facilitate the connecting of the circuit breakers to the power relays. 
     As is conventional, circuit breakers  60 ,  62 ,  64 ,  66 , and  68  may be toggled between off-positions wherein the corresponding power relays  77 ,  79  and  92  are isolated from utility source  42  and on-positions wherein the corresponding power relays  77 ,  79  and  92  are protected from the potential overload by utility source  42 . 
     Generator  44  is interconnected to ground  100  through line  102 , and supplies ±120 volts across lines  104  and  106 . Lines  104  and  106  are connected to corresponding bus bars  108  and  110 , respectively, which are mounted to rear panel  22  of cabinet  14 . A plurality of single pole circuit breakers  114  and  116  are interconnected to bus bar  108 . Similarly, a plurality of single pole circuit breakers  118  and  120  are interconnected to bus bar  110 . Circuit breakers  114 ,  116 ,  118 , and  120  are operatively connected to corresponding individual branch circuits within the building which require 120 volt service, in a manner hereinafter described. A double-pole circuit breaker  122  is interconnected to both bus bars  108  and  110  and is operatively connected to a corresponding individual branch circuit within the building which requires 240 volt service, in a manner hereinafter described. 
     Circuit breakers  114  and  118  are interconnected to normally opened contacts  124  and  126 , respectively, of power relay  77  by corresponding lines  128  and  130 , respectively. Circuit breakers  116  and  120  are interconnected to normally open contacts  132  and  134 , respectively, of power relay  79  through corresponding lines  136  and  138 , respectively. Double-pole circuit breaker  122  is interconnected to normally open contacts  140  and  142  of relay  92  through corresponding lines  144  and  146 , respectively. 
     As is conventional, circuit breakers  114 ,  116 ,  118 ,  120  and  122  may toggle between off-positions wherein the corresponding power relays  77 ,  79  and  92  are isolated from generator  44  and on-positions wherein the corresponding power relays  77 ,  79  and  92  are protected from potential overload by generator  44 . 
     Power relay  92  includes a magnetic coil K 1  having terminals A and B. Terminal A of power relay  92  is interconnected to normally open contact  140  by line  150 . Terminal B of power relay  92  is interconnected to normally open contact  142  by line  152 . Similarly, power relays  77  and  79  include corresponding magnetic coils K 3  and K 2 , respectively, having terminals A and B. Terminal A of power relay  79  is interconnected to normally open contact  132  by line  154 . Terminal B of power relay  79  is interconnected to normally opened contact  134  by line  156 . Likewise, terminal A of power relay  77  is interconnected to normally open contact  124  by line  158  and terminal B of power relay  77  is interconnected to normally open contact  126  by line  160 . 
     The common terminals  162  and  164  of power relay  77  are connected by lines  166  and  168 , respectively, to corresponding individual branch circuits within the building which require 120 volt service. Common terminals  170  and  172  are interconnected by lines  174  and  176 , respectively, to corresponding individual branch circuits within the building which also require 120 volt service. Common terminals  178  and  180  of power relay  92  are interconnected by lines  182  and  184 , respectively, to a corresponding branch circuit within the building which requires 240 volt service. Referring to FIGS. 2 and 3, it is contemplated to mount a terminal block  186  on rear panel  22  of cabinet  14  in order to facilitate connecting of the common terminals of the power relays to various loads. 
     Under normal operating circumstances, main circuit breaker  54  and circuit breakers  60 ,  62 ,  64 ,  66  and  68  are toggled to their on-positions. Movable contacts  190  and  192  of power relay  77  are engaged with normally closed contacts  70  and  76 , respectively; movable contacts  194  and  196  of power relay  79  are engaged with normally closed contacts  72  and  74 , respectively; and movable contacts  198  and  200  of power relay  92  are engaged with normally closed contacts  88  and  90 , respectively. As described, utility source  42  provides power on lines  50  and  52  to corresponding loads. 
     As best seen in FIG. 4, a monitoring circuit  188  is operatively connected to utility source  42  and generator  44 . As is conventional, monitoring circuit  188  monitors the power supplied by utility source  42 . In response to a power outage from utility source  42 , monitoring circuit  188  starts the internal combustion engine of generator  44 . As heretofore described, a starting of the internal combustion motor causes the electrical generator of generator  44  to generate electrical power across lines  104  and  106 . 
     With circuit breakers  114  and  118  toggled to their on-positions, current flows through magnetic coil K 3  of power relay  77  such that the magnetic coil K 3  becomes magnetized and attracts movable contacts  190  and  192  within power relay  77 . As a result, movable contacts  190  and  192  disengage from normally closed contacts  70  and  76 , respectively, and close against corresponding normally open contacts  124  and  126 , respectively, so as to operatively connect corresponding loads to generator  44 . 
     With circuit breakers  116  and  120  toggled to their on-positions, current flows through magnetic coil K 2  of power relay  79  such that the magnetic coil K 2  becomes magnetized and attracts movable contacts  194  and  196  within power relay  79 . As a result, movable contacts  194  and  196  disengage from normally closed contacts  72  and  74 , respectively, and close against corresponding normally open contacts  132  and  134 , respectively, so as to operatively connect corresponding loads to generator  44 . 
     With circuit breaker  122  toggled to its on-position, current flows through magnetic coil K 1  of power relay  92  such that the magnetic coil K 1  becomes magnetized and attracts movable contacts  198  and  200  within power relay  92 . As a result, movable contacts  198  and  200  disengage from normally closed contacts  88  and  90 , respectively, and close against corresponding normally open contacts  140  and  142 , respectively, so as to operatively connect a corresponding load to generator  44 . 
     In response to the restoration of power from utility source  42 , monitoring circuit  188  stops the internal combustion engine of generator  44 . By stopping the internal combustion engine, the electrical generator of generator  44  no longer generates power across lines  104  and  106  and current ceases to flow through magnetic coils K 1 , K 2  and K 3  of power relays  92 ,  79  and  77 , respectively. As a result, movable contacts  190  and  192  of power relay  77  disengage from normally open contacts  124  and  126 , respectively, and reclose against corresponding normally closed contacts  70  and  76 , respectively, so as to operatively connect corresponding loads to utility source  42 . 
     Similarly, movable contacts  194  and  196  disengage from normally open contacts  132  and  134 , respectively, and reclose against corresponding normally closed contacts  72  and  74 , respectively, so as to operatively connect corresponding loads to utility source  42 . In addition, movable contacts  198  and  200  disengage from normally open contacts  140  and  142 , respectively, and reclose against corresponding normally closed contacts  88  and  90 , respectively, so as to operatively connect a corresponding load to utility source  42 . Thereafter, monitoring system  188  continues to monitor the power supplied by utility source  42  and repeats the above-described process if a power outage from utility source  42  is detected. 
     Referring to FIG. 5, an alternate embodiment of the transfer mechanism is shown. The alternate embodiment of the transfer mechanism is generally designated by the reference numeral  202 . Transfer mechanism  202  is identical in structure to transfer mechanism  10  with the exception of time delay switches  204 ,  206  and  208  as hereinafter described. As such, common reference characters will be utilized. 
     In order to sequentially bring the various loads on line with generator  44 , a first time delay switch  204  is positioned between magnetic coil K 1  of power relay  92  and normally open contact  142 ; a second time delay switch  206  is positioned between magnetic coil K 2  of power relay  79  and normally open contact  134 ; and a third time delay switch  208  is positioned between magnetic coil K 3  of power relay  77  and normally open contact  126 . As generator  44  is started as heretofore described, time delay switches  204 ,  206  and  208  are normally open so as to prevent the flow of current through magnetic coils K 1 , K 2  and K 3 , respectively. Thereafter., time delay switches  204 ,  206  and  208  are sequentially closed over a predetermined time period in order to allow for the flow of current through corresponding magnetic coils K 1 , K 2  and K 3 , respectively. As current flows through each magnetic coil K 1 , K 2  and K 3 , various loads are operatively connected to generator  44  in the matter heretofore described with respect to transfer switch  10 . 
     Further, in the second embodiment, it can be appreciated to utilize DC control relays in place of power relays  77 ,  79  and  92  and driving them directly using staggered delays. 
     Referring to FIG. 6, an example of a relay for use in accordance with the present invention is generally designated by the reference numeral  220 . Relay  220  includes a first terminal  222  having first and second opposite ends  224  and  226 , respectively. First end  224  is intended to be operatively connected to utility source  42  through screw  228 . Stationary contact  230  is mounted to the second end  226  of terminal  222  as hereinafter described. 
     Referring to FIGS. 7 and 8, stationary contact  230  includes a backing portion  232  formed of pure copper. Backing portion  232  of stationary contact  230  includes a first contacting portion engaging surface  234  and a second, terminal engaging surface  236  spaced therefrom by an outer edge  238 . The diameter of the contacting portion engaging surface  234  is less than the diameter of the terminal engaging surface  236  such that outer edge  238  of backing portion  232  is tapered. 
     Mounting head  240  extends from terminal engaging surface  236  and has a diameter less than the diameter of opening  242  in second end  226  of terminal  222 . As best seen in FIG. 7, mounting head  240  extends through opening  242  in second end  226  of terminal  222 . Terminal end  243  of mounting head  230  is either melted or swagged onto side  222   a  of terminal  222  so as to capture terminal  222  between terminal end  243  of mounting head  240  and terminal engaging surface  236  of stationary contact  230  so as to retain stationary contact  230  on second end  226  of terminal  222 . 
     Stationary contact  230  further includes a contacting portion  244  deposited on contacting portion engaging surface  234  of backing portion  232  of stationary contact  230 . Contacting portion  244  is formed of pure tungsten and includes a backing portion engaging surface  246  which overlaps the contacting portion engaging surface  234  of backing portion  232  of stationary contact  230 . Contacting portion  244  of stationary contact  230  further includes contacting surface  248  which is spaced from backing portion engaging surface  246  thereof by an outer edge  250 . Contacting surface  248  of contacting portion  244  of stationary contact  230  has a diameter which is less than the diameter of backing portion engaging surface  246  such that outer edge  250  of contacting portion  244  of stationary contact  230  is generally tapered. 
     Referring back to FIG. 6, relay  220  further includes a second terminal  252  having first and second opposite ends  254  and  256 , respectively. End  254  of second terminal  252  may be connected to stand-by generator  44  through screw  258 . Second stationary contact  260  is interconnected to second end  256  of second terminal  252 . Second stationary contact  260  is identical in structure to first stationary contact  230 , and as such, the description heretofore of stationary contact  230  is understood to describe second stationary contact  260  as if fully described herein. In addition, second stationary contact  260  is mounted to second end  256  of second terminal  252  in the same manner as first stationary contact  230  is mounted to second end  226  of first terminal  222 . As such, the description heretofore of the mounting of first stationary contact  230  to second end  226  of first terminal  222  is understood to describe the mounting of second stationary contact  260  to second end  256  of second terminal  252  as if fully described herein. 
     Relay  220  further includes an arm  262  pivotably mounted to support  264  extending vertically from an upper surface  266  of relay  220 . Arm  262  includes a first end  267  and a second, opposite end  268  having first and second movable contacts  270  and  272 , respectively, mounted on corresponding sides  262   a  and  262   b  thereof. Arm  262  is movable between a first position, FIG. 6, wherein first movable contact  270  engages first stationary contact  230  and a second position wherein second movable contact  272  engages second stationary contact  260 . Spring  274  has a first end  276  mounted to the upper surface  266  of relay  220  and a second, opposite end  278  engaging first end  267  of arm  262  so as to urge arm  262  towards the first position. 
     As hereinafter described, first and second movable contacts  270  and  272 , respectively, are identical in structure, and as such, the description hereinafter of first movable contact  270  is understood to describe second movable contact  272  as if fully described hereinafter. Referring to FIGS. 7 and 9, first movable contact  270  includes backing portion  280  formed of pure copper. Backing portion  280  includes an arm engaging portion  282  which is secured to second end  268  of arm  262  in any suitable manner. Backing portion  280  of movable contact  270  further includes contacting portion engaging surface  284  which is spaced from arm engaging surface  282  by outer edge  286 . Contacting portion engaging surface  284  of movable contact  270  has a diameter less than arm engaging surface  282  of movable contact  270  such that outer edge  286  of backing portion  280  of first movable contact  270  is tapered. 
     First movable contact  270  further includes a contacting portion  288  having a backing portion engaging surface  290  which overlaps and engages contacting portion engaging surface  284  of backing portion  280  of first movable contact  270 . Contacting portion  288  has a contacting surface  292  directed towards first stationary contact  230 . Contacting surface  292  of contacting portion  288  has a generally arcuate shape and terminates at a crown  294 . Contacting surface  292  of contacting portion  288  of first movable contact  270  is spaced from backing portion engaging surface  290  of contacting portion  288  of first movable contact  270  by an outer edge  296 . The diameter of contacting surface  292  of contacting portion  299  of first movable contact  270  has a diameter less than the diameter of backing portion engaging surface  290  of contacting portion  288  of first movable contact  270  such that outer edge  296  of contacting portion  288  of first movable contact  270  is tapered. 
     Referring to FIG. 10, an alternate embodiment of a movable contact is generally designated by the reference numeral  310 . Movable contact  310  is formed from silver cadmium oxide and takes the form a rivet. Movable contact  310  includes a first contacting portion  312  having a mounting head  314  extending therefrom. Mounting head  314  extends from a terminal engaging surface  316  of first contacting portion  312  and has a diameter less than the diameter of opening  318  in arm  262 . 
     Mounting head  314  extends through opening  318  in arm  262  wherein a second contacting portion  320  is riveted thereon. Second contacting portion  320  includes a terminal engaging surface  322  and a contacting surface  324 . Similarly, First contacting portion  310  also includes a contacting surface  326 . It can be appreciated that contacting surfaces  326  and  324  of first and second contacting portions  312  and  320 , respectively, are tapered to facilitate electrical contact with corresponding stationary contacts  260  and  230 . 
     Referring to FIG. 6, arm  262  is electrically connected to load terminal  300  through line  302 . Load terminal  300  may be connected to a load through screw  304 . In addition, the coil of relay  220  is electrically connected to stand-by generator  44  through screw  306  such that relay  220  operates in a such a manner as heretofore described with respect to power relays  77 ,  79  and  92 . 
     Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.