Apparatus and method for preventing an electrical backfeed

Abstract

At least one aspect is directed to a transfer switch including a first input to couple a first multiphase low voltage electrical supply to the transfer switch, and a second input to couple a second multiphase low voltage electrical supply to the transfer switch. The transfer switch also includes a first set of switches in electrical communication with the first input and a second set of switches in electrical communication with the second input. A control module monitors and controls operation of both the first set of switches and the second set of switches to detect a malfunction of any switches included in at least one of the first set of switches and the second set of switches and prevent the first input from being placed in electrical communication with the second input.

What is claimed is: 
     
       1. A transfer switch comprising:
 a first input to couple a first multiphase low voltage electrical supply to the transfer switch; 
 a first set of switches in electrical communication with the first input; 
 a second input to couple a second multiphase low voltage electrical supply to the transfer switch; 
 a second set of switches in electrical communication with the second input; 
 an output to couple the transfer switch to a load; 
 a third set of switches coupled in series between the second set of switches and the output; and 
 a control module to monitor and control operation of the first set of switches, the second set of switches and the third set of switches to selectively couple the first input and the second input to the output and to detect a malfunction of any switches included in at least one of the first set of switches, the second set of switches and the third set of switches and to prevent the first input from being placed in electrical communication with the second input, 
 wherein the second set of switches are coupled in series between the first set of switches and the third set of switches. 
 
     
     
       2. The transfer switch as claimed in  claim 1 , further comprising a switching module comprising:
 a switch included in the first set of switches; 
 a switch included in the second set of switches; and 
 a switch included in the third set of switches. 
 
     
     
       3. The transfer switch as claimed in  claim 2 , wherein the switching module further comprises:
 each switch included in the first set of switches; 
 each switch included in the second set of switches; and 
 each switch included in the third set of switches. 
 
     
     
       4. The transfer switch as claimed in  claim 2 , further comprising a plurality of switching modules. 
     
     
       5. The transfer switch as claimed in  claim 1 , wherein the first input is adapted to couple to a first split-phase electrical supply, and 
       wherein the second input is adapted to couple to a second split-phase electrical supply. 
     
     
       6. The transfer switch as claimed in  claim 5 , wherein the first input is adapted to couple to a first 240 volt split-phase electrical supply, and 
       wherein the second input is adapted to couple to a second 240 volt split-phase electrical supply. 
     
     
       7. The transfer switch as claimed in  claim 6 , wherein at least one of the first input and the second input is adapted to couple to a power source selected from a group consisting of a generator, an uninterruptible power supply and an alternative energy source. 
     
     
       8. The transfer switch as claimed in  claim 1 , wherein the first set of switches comprises a first pair of switches and the second set of switches comprises a second pair of switches. 
     
     
       9. The transfer switch as claimed in  claim 8 , the first set of switches further comprising two single pole double throw switches, and the second set of switches further comprising two single pole double throw switches. 
     
     
       10. The transfer switch as claimed in  claim 9 , the first set of switches further comprising a first relay comprising at least one single pole double throw switch; and
 the second set of switches further comprising a second relay comprising at least one single pole double throw switch. 
 
     
     
       11. The transfer switch as claimed in  claim 8 , wherein the first pair of switches comprises a first switch and a second switch,
 wherein the control module is coupled to a load side of the first switch to receive a first control signal, 
 wherein the control module is coupled to a load side of the second switch to receive a second control signal, and 
 wherein the control module is adapted to detect a malfunction of the first set of switches by a state of at least one of the first control signal and the second control signal. 
 
     
     
       12. The transfer switch as claimed in  claim 11 , wherein the second pair of switches comprises a first switch and a second switch,
 wherein the control module is coupled to a load side of the first switch of the second pair of switches to receive a third control signal, 
 wherein the control module is coupled to a load side of the second switch of the second pair of switches to receive a fourth control signal, and 
 wherein the control module is adapted to detect a malfunction of the second set of switches by a state of at least one of the third control signal and the fourth control signal. 
 
     
     
       13. The transfer switch as claimed in  claim 1 , wherein a malfunction of the third set of switches is sensed by a presence of voltage at the output. 
     
     
       14. The transfer switch as claimed in  claim 1 , wherein a malfunction of the third set of switches is sensed by current flow through any of the switches comprising the third set of switches. 
     
     
       15. The transfer switch as claimed in  claim 1 , wherein the malfunction includes a welded contact. 
     
     
       16. The transfer switch as claimed in  claim 1 , wherein the third set of switches are operable in at least a first position and a second position,
 wherein the second set of switches are coupled to the output when the third set of switches are located in the first position, and 
 wherein the second set of switches are coupled to a test load when the third set of switches are located in the second position. 
 
     
     
       17. The transfer switch as claimed in  claim 1 , wherein the third set of switches are operable in at least a first position and a second position,
 wherein the second set of switches are coupled to the output when the third set of switches are located in the first position, 
 wherein the second set of switches are disconnected from the output when the third set of switches are located in the second position, and 
 wherein the output is coupled to a current source when the third set of switches are located in the second position. 
 
     
     
       18. The transfer switch as claimed in  claim 1 , wherein the second set of switches are operable in at least a first position and a second position,
 wherein the first set of switches are electrically isolated from the third set of switches by the second set of switches when the second set of switches are located in the first position, and 
 wherein the first set of switches are placed in electrical communication with the third set of switches by the second set of switches when the second set of switches are located in the second position. 
 
     
     
       19. A method of preventing a backfeed through a transfer switch, the transfer switch comprising a first input coupled to a first switch and adapted to receive a first multiphase low voltage power from a first power source, a second input coupled to a second switch and adapted to receive a second multiphase low voltage power from a second power source, an output and a third switch coupled to the output, the method comprising:
 connecting the first input to the output at least in part by operating the second switch to connect the first switch to the third switch; 
 initiating a transfer to disconnect the output from the first input and connect the output to the second input at least in part by operating the second switch to connect the second input to the third switch; 
 operating a plurality of sets of switches to complete the transfer; 
 monitoring at least one of the plurality of sets of switches to detect a malfunction of any switches; and 
 stopping the transfer if a malfunction is detected to prevent the first input from being placed in electrical communication with the second input. 
 
     
     
       20. The method of  claim 19 , wherein the act of initiating comprises an act of detecting a voltage decrease at the first input. 
     
     
       21. The method of  claim 19 , wherein the act of monitoring comprises an act of voltage sensing. 
     
     
       22. The method of  claim 21 , further comprising acts of:
 sensing whether the first switch is operative by sensing a voltage at a load side of the first switch; 
 sensing whether the second switch is operative by sensing a voltage at a load side of the second switch; and 
 sensing whether the third switch is operative by sensing a voltage at a load side of the third switch. 
 
     
     
       23. The method of  claim 22 , wherein each of the acts of sensing further comprise an act of detecting a welded contact by the presence of a voltage. 
     
     
       24. The method of  claim 19 , further comprising an act of sensing whether a switch is in a position that is inconsistent with a state established for the switch by control logic. 
     
     
       25. The method of  claim 19 , wherein the first input is adapted to couple to a first split-phase low voltage power source and the second input is adapted to couple to a second split-phase low voltage power source. 
     
     
       26. The method of  claim 19 , wherein each of the plurality of sets of switches comprises a pair of switches. 
     
     
       27. The method of  claim 19 , further comprising an act of sensing that a switch connected to the output is inoperative when a current is flowing through the switch connected to the output. 
     
     
       28. A transfer switch comprising:
 a first input to couple a first multiphase low voltage electrical power supply to the transfer switch;
 a first set of switches in electrical communication with the first input; 
 a second input to couple a second multiphase low voltage electrical power supply to the transfer switch; 
 a second set of switches in electrical communication with the second input; 
 an output to couple the transfer switch to a load; 
 a third set of switches coupled in series between the second set of switches and the output; and 
 means for detecting a malfunction in any of the first set of switches, the second set of switches and the third set of switches, and upon detecting a malfunction, preventing a connection of at least one of the first input and the second input to the output, 
 wherein the second set of switches are coupled in series between the first set of switches and the third set of switches. 
 
 
     
     
       29. The transfer switch as claimed in  claim 28 , further comprising a switching module comprising:
 a switch included in the first set of switches; 
 a switch included in the second set of switches; and 
 a switch included in the third set of switches. 
 
     
     
       30. The transfer switch as claimed in  claim 29 , further comprising a plurality of switching modules. 
     
     
       31. The transfer switch as claimed in  claim 28 , wherein the means for detecting a malfunction detects a malfunction of a switch in the first set of switches when a voltage is present on a load side of the switch. 
     
     
       32. The transfer switch as claimed in  claim 28 , wherein the means for detecting a malfunction detects a malfunction of a switch in the second set of switches when a voltage is present on a load side of the switch. 
     
     
       33. The transfer switch as claimed in  claim 28 , wherein the first input is adapted to couple to a first split-phase low voltage power supply and the second input is adapted to couple to a second split-phase low voltage power supply. 
     
     
       34. The transfer switch as claimed in  claim 33 , wherein the first input is adapted to couple to a first 240 volt split-phase power supply and the second input is adapted to couple to a second 240 volt split-phase power supply. 
     
     
       35. The transfer switch as claimed in  claim 28 , wherein the second input is adapted to couple to a power supply selected from a group consisting of a utility source, a generator, an uninterruptible power supply and an alternative energy source. 
     
     
       36. The transfer switch as claimed in  claim 28 , wherein, upon detecting a malfunction, the means for detecting a malfunction generate a fault indication. 
     
     
       37. The transfer switch as claimed in  claim 28 , wherein each of the first set of switches and the second set of switches comprises a pair of switches. 
     
     
       38. A transfer switch comprising:
 a first input to couple to a first power source;   a second input to couple to a second power source;   an output to provide output power;   a first switching module coupled to the first input, the second input and the output and configured to selectively couple one of the first input and the second input with the output;   a second switching module coupled to the first input, the second input and the output and configured to selectively couple one of the first input and the second input with the output;   an interface configured to allow a user to select a single phase configuration or a multiphase configuration for each of the first switching module and the second switching module; and   a control device coupled to the interface and the first switching module and the second switching module and configured to prevent the first input from being placed in electrical communication with the second input for the multiphase configuration of either the first switching module or the second switching module.   
     
     
       39. The transfer switch of claim 38, wherein the control device is configured to detect a loss of power at the first input and to control each of the first switching module and the second switching module to disconnect the output from the first input and connect the output to the second input while isolating the first input from the second input. 
     
     
       40. The transfer switch of claim 39, wherein the output includes a first output line and a second output line and wherein the first switching module is coupled to the first output line and the second switching module is coupled to the second output line. 
     
     
       41. The transfer switch of claim 38, wherein each of the first input and the second input includes a first line and a second line, and in the multiphase configuration, the first line of the first input and the first line of the second input are coupled to the first switching module and the second line of the first input and the second line of the second input are coupled to the second switching module. 
     
     
       42. The transfer switch of claim 41, further comprising a third input, a fourth input and a second output and a third switching module coupled to the third input, the fourth input and the second output and configured to selectively couple one of the third input and the fourth input with the second output. 
     
     
       43. The transfer switch of claim 38, wherein the first switching module has at least one switch, and wherein the control device is configured to detect a failure of the at least one switch. 
     
     
       44. A method of switching multiple power sources to a load using a transfer switch having at least a first switching module and a second switching module, the method comprising:
 coupling a first power source to the first switching module and to the second switching module;   coupling a second power source to the first switching module and to the second switching module;   configuring a user interface of the transfer switch to allow a user to select between a single phase mode of operation and a multiphase mode of operation for each of the first switching module and the second switching module;   monitoring at least one of the first switching module and the second switching module to detect a malfunction within the at least one of the first switching module and the second switching module; and   preventing a transfer of power from the first power source to the second power source upon detection of a malfunction.   
     
     
       45. The method of claim 44, further comprising coupling a first load to an output of the first switching module and to an output of the second switching module and providing 240 volt AC power to the first load. 
     
     
       46. The method of claim 45, further comprising coupling a third power source to a third switching module of the transfer switch. 
     
     
       47. The method of claim 46, further comprising coupling a second load to an output of the third switching module and providing 120 volt single phase power to the second load. 
     
     
       48. The method of claim 44, further comprising selecting a single phase mode of operation for each of the first switching module and the second switching module, and coupling a first load to the first switching module and coupling a second load to the second switching module and providing 120 volt single phase power to the first load and to the second load. 
     
     
       49. The method of claim 44, wherein:
 the first power source and the second power source are split-phase power sources;   coupling a first power source to the first switching module and to the second switching module includes coupling the first switching module to a first phase line of the first power source and coupling the second switching module to a second phase line of the first power source; and   coupling a second power source to the first switching module and to the second switching module includes coupling the first switching module to a first phase line of the second power source and coupling the second switching module to a second phase line of the second power source.   
     
     
       50. A transfer switch comprising:
 a first input to couple to a first power source;   a second input to couple to a second power source;   an output to provide output power;   a first switching module coupled to the first input, the second input and the output and configured to selectively couple one of the first input and the second input with the output;   a second switching module coupled to the first input, the second input and the output and configured to selectively couple one of the first input and the second input with the output;   means tor selecting a single phase configuration or a multiphase configuration for each of the first switching module and the second switching module and means for preventing the first input from being placed in electrical communication with the second input for the multiphase configuration.   
     
     
       51. The transfer switch of claim 50, further comprising means for detecting a loss of power at the first input and for controlling each of the first switching module and the second switching module to disconnect the output from the first input and connect the output to the second input while isolating the first input from the second input. 
     
     
       52. The transfer switch of claim 50, wherein the output includes a first output line and a second output line and wherein the first switching module is coupled to the first output line and the second switching module is coupled to the second output line. 
     
     
       53. The transfer switch of claim 50, wherein each of the first input and the second input includes a first line and a second line, and in the multiphase configuration, the first line of the first input and the first line of the second input are coupled to the first switching module and the second line of the first input and the second line of the second input are coupled to the second switching module. 
     
     
       54. The transfer switch of claim 53, further comprising a third input, a fourth input and a second output and a third switching module coupled to the third input, the fourth input and the second output and configured to selectively couple one of the third input and the fourth input with the second output. 
     
     
       55. The transfer switch of claim 50, wherein the first switching module has at least one switch, and wherein the transfer switch further includes means for detecting a failure of the at least one switch.