Abstract:
Hybrid power relay for making and breaking an electrical circuit which includes electromagnetically operated contacts for making and breaking the circuit, a solid state switch connected across the contacts, a control circuit responsive to a control signal for actuating the solid state switch and the contacts such that the solid state switch closes before the contacts to make the circuit and the contacts open before the solid state switch to break the circuit, and a protective circuit for monitoring the temperature of the solid state switch and opening the switch in the event of a rise in temperature produced by abnormal current flow in the switch due to failure of the contacts to make and maintain the circuit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This invention pertains generally to relays for opening and closing electrical power circuits and, more particularly, to a hybrid power relay having both electromechanical and solid state switching elements. 
         [0003]    2. Related Art 
         [0004]    The two most common types of switching devices currently available for making and breaking electrical power circuits are electromechanical contactors or relays having mechanical contacts that can be opened or closed by electromagnetic forces, and solid state relays or switches which have no mechanical switching contacts. 
         [0005]    The mechanical contacts can generally carry higher electrical currents and thus be used for heavier loads than solid state switching devices, but they are subject to arcing when opened or closed. The solid state devices generally require large heat sinks to protect them from overheating. 
         [0006]    Heretofore, there have been some attempts to provide hybrid power relays having both electromechanical contacts and solid state switching, and examples of such devices are found in U.S. Pat. Nos. 2,789,253, 3,237,030, 3,321,668, 3,558,910, 3,639,808, 4,074,333, 5,283,706, 5,528,443, 5,790,354, 6,347,024, and 6,621,668. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0007]    It is, in general, an object of the invention to provide a new and improved hybrid power relay. 
         [0008]    Another object of the invention is to provide a hybrid power relay of the above character which overcomes the limitations and disadvantages of power relays heretofore provided. 
         [0009]    These and other objects are achieved in accordance with the invention by providing a hybrid power relay for making and breaking an electrical circuit which includes electromagnetically operated contacts for making and breaking the circuit, a solid state switch connected across the contacts, means responsive to a control signal for actuating the solid state switch and the contacts such that the solid state switch closes before the contacts to make the circuit and the contacts open before the solid state switch to break the circuit, and means for monitoring the temperature of the solid state switch and opening the switch in the event of a rise in temperature produced by abnormal current flow in the switch due to failure of the contacts to make and maintain the circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a circuit diagram of one embodiment of a hybrid power relay incorporating the invention. 
           [0011]      FIGS. 2A-2D  are block diagrams illustrating use of the embodiment of  FIG. 1  in both three-phase systems and single-phase systems. 
           [0012]      FIG. 3  is an exploded isometric view, partly exploded of another embodiment of a hybrid power relay according to the invention. 
           [0013]      FIG. 4  is a view similar to  FIG. 3  with the solid state switch module mounted on the contactor. 
           [0014]      FIG. 5  is a top plan view of the embodiment of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    In  FIG. 1 , the invention is illustrated in connection with a conventional three-phase, three wire alternating current (AC) electrical power system having line conductors L 1 , L 2 , and L 3 . However, it will be understood that the invention can be also be employed with other power systems, including three-phase, four wire systems and single-phase systems. 
         [0016]    The hybrid power relay includes a mechanical switching section  11  that includes three sets of contacts  12 ,  13 , and  14  for making and breaking electrical circuits between the line conductors and a three-phase load  16  represented by resistors  17 ,  18 , and  19  which are shown as being connected in a Y-configuration. The contacts are electromagnetically operated and can, for example, be the contacts of one or more electromechanical relays (EMRs), contactors, or definite purpose contactors. In the embodiment illustrated, opening and closing of the contacts is controlled by a single operating coil  21  which is shown in the mechanical driver section  22  of the device. 
         [0017]    The relay also has an electronic switching section  26  with solid state switches  27 ,  28 ,  29  connected in parallel with, or across, contacts  12 ,  13 , and  14 , and a solid state driver  31  for the switches. Each of the electronic switches has a pair of silicon controlled rectifiers (SCRs)  32 ,  33  connected back-to-back across the associated contacts, with the cathode of SCR  32  and the anode of SCR  33  connected to one of the contacts and the anode of SCR  32  and the cathode of SCR  33  connected to the other contact. 
         [0018]    Trigger signals are applied to the control gates of the SCRs by optocouplers  34 ,  36  which are shared between the switching section and the driver stage. Each of the optocouplers has a light emitting diode (LED)  34   a,    36   a  coupled optically to a photodiode  34   b,    36   b  which produces a DC output voltage in response to light produced by application of an input signal to the LED. One of the outputs of each of the optocouplers is connected to the control gate of one of the SCRs  32 ,  33  through a coupling resistor  37 ,  38 , and a matching network consisting of a resistor  39  and an inductor  41  is connected between the other outputs of the optocouplers. Transient Voltage Suppressors (TVSs)  42 ,  43  are connected across the outputs of the optocouplers to suppress transient voltages and protect the solid state devices from voltage spikes. 
         [0019]    In the driver stage, the inputs of all six of the optocouplers  34 ,  36  are connected in series between input terminals  46 ,  47 , and an input resistor  48  also connected between the terminals. 
         [0020]    Operating power for the solid state switches is provided by a direct current (DC) power supply  51  which includes a bridge rectifier  52 . The positive output of the bridge rectifier is connected to input terminal  46  via a light emitting diode  53  and a resistor  54 , and the negative output is connected to a ground line  56 . A Zener diode  57  and a capacitor  58  are connected across the outputs of the bridge rectifier to regulate and smooth the DC output. 
         [0021]    A thermal protection circuit  59  turns off the solid state switches in the event of over-heating of the SCRs as might, for example, happen if the relay contacts were to fail to close or to maintain a circuit and excessive current were to flow through the SCRs as a result. This circuit includes a temperature sensor which, in this particular embodiment, consists of a thermistor  61  positioned in close proximity to the SCRs in all three of the switches. The thermistor is connected in series with a dropping resistor  62  between the positive output line  63  of the DC power supply and ground line  56  to provide a voltage across the thermistor corresponding to the resistance of the thermistor and, hence, the temperature to which it is subjected. 
         [0022]    The voltage developed across the thermistor is applied to the positive input of a comparator  64 , and a reference voltage provided by a voltage divider consisting of resistors  66 ,  67  connected between the positive supply line and ground is applied to the negative input of the comparator. The output of the comparator is connected to input terminal  47  of drive stage  31 . As long as the thermistor voltage is below the level of the reference voltage, the output of the comparator remains low, input terminal  47  is maintained at or near the DC ground potential, the voltage between input terminals  46  and  47  is large enough to drive optocouplers  34 ,  36  to provide the bias necessary to keep SCRs  34 ,  36  in the ON state. A capacitor  68  is connected between the negative input of the comparator and ground to provide AC filtering and eliminate fluctuations in the state of the comparator. 
         [0023]    Operating coil  21  and DC power supply  51  are energized by current from the AC power system, represented as an AC source  69 , through a control circuit  71 . The control circuit includes a solid state switch or relay  72  similar to switches  27 - 29 , with a pair of SCRs  73 ,  74  connected back-to-back in series with coil  21  between lines L 1 , L 2  of the AC power system. The operating coil is connected in parallel with the input of the DC supply, and input current is supplied to bridge rectifier  52  from lines L 1 , L 2  through a capacitor  75  and a resistor  76 . A metal oxide varistor  77  is connected across the coil and the input of the DC supply to suppress transient voltages and protect the solid state switching devices from voltage spikes when the coil is energized and the solid state switching devices are receiving their control signals. 
         [0024]    Like solid state switches  27   29 , The AC switch or control circuit also includes a pair of optocouplers  78 ,  79  with first outputs connected to the control gates of SCRs  73 ,  74  via resistors  81 ,  82  and second outputs connected together through a matching network consisting of a resistor  83  and an inductor  84 . Transient Voltage Suppressors (TVSs)  86 ,  87  are connected across the outputs of the optocouplers to suppress transient voltages and protect the solid state devices from voltage spikes. 
         [0025]    The AC switch is controlled by a low voltage, e.g. 5 volt, DC control signal applied to input terminals  88 ,  89 . The inputs of optocouplers  78 ,  79  are connected in series, and the control signal is applied to them through a voltage divider consisting of resistors  91 ,  92  connected between the input terminals and the inputs of the optocouplers. 
         [0026]    In the absence of the control signal, SCRs  73 ,  74  remain in an OFF state, with relay coil  21  and DC power supply  51  both de-energized, relay contacts  12   14  and solid state switches  27   29  all open, and no current flowing to the load. 
         [0027]    Upon the application of a DC control signal to input terminals  88 ,  89 , optocouplers  78 ,  79  deliver trigger signals which turn on SCRs  73 ,  74 , thereby simultaneously energizing operating coil  21  and DC supply  51 . The output voltage from the DC supply turns on optocouplers  34 ,  36  which deliver trigger signals to SCRs  32 ,  33 , thereby turning on the SCRs to connect the three-phase load  16  to AC supply lines L 1 , L 2 , L 3 . This happens almost instantaneously, with SCRs  32 ,  33  typically being fully turned on less than 100 microseconds after the power supply is energized. 
         [0028]    Although the operating coil is energized at the same time as the DC power supply, due to the inherent delay in the build-up of the coil(s magnetic field and the subsequent travel time of the EMR contacts, the contacts do not close until several milliseconds after the coil is energized and well after the solid state switches have fully switched on the load current in each phase. 
         [0029]    Being turned on first, the SCRs conduct the initial load currents and any associated transient currents with virtually no arcing. When the contacts close, the voltage across them is equal to the forward voltage drop across the SCRs, which is typically on the order of only 1.1 to 1.4 volts. Hence, there is no arcing across the contacts, and no transients are generated by their closing. 
         [0030]    Once the contacts are closed, the voltage drop across them and across the SCRs is lower than the minimum operating voltage of the SCRs. This causes the SCRs to open, with the load current thereafter being carried entirely by the EMR contacts, thereby avoiding heating of the SCRs and the need for heat sinks or other cooling. 
         [0031]    To open the circuits and disconnect the load from the lines, the control signal is removed from AC switch  72 , which causes SCRs  73 ,  74  to open on the next zero crossings of the current through them, thereby de-energizing operating coil  21  and DC supply  51 . The EMR contacts are urged toward their open positions by a return spring, and when the coil(s magnetic field falls to the point that it is overcome by the force of the spring, contacts  12   14  begin to open. 
         [0032]    Even though the DC supply has been turned off, charge stored in capacitor  58  continues to supply operating voltage to optocouplers  34 ,  36 , and the optocouplers continue to bias the SCRs  32 ,  33  for conduction. At the instant the contacts begin to open, the voltages across the SCRs begin to rise, and the SCRs turn back on, typically in less than 100 microseconds, extinguishing any arc that might result from the opening of the contacts. The SCRs remain turned on for approximately one AC cycle, typically about 16 to 20 milliseconds, depending upon the line frequency, which permits the contacts to open fully and return to their fully off position. The SCRs stop conducting load current at the next zero crossing of the current in each phase, without the transients that typically occur when EMR contacts open. This completely eliminates the electrical noise and mechanical damage that might otherwise occur, thereby extending the life of the contacts significantly. 
         [0033]    In the event that one or more of the SCRs should overheat or if the ambient temperature should become too high, the voltage developed across thermistor  61  will exceed the threshold level set by resistors  66 ,  67 , causing comparator  64  to switch to from its low output state to its high output state, thereby interrupting the current to optocouplers  34 ,  36  and turning off SCRs  32 ,  33 . Such overheating might, for example, occur if one or more of the EMR contacts should fail to close or to maintain a closed circuit. The SCRs will remain turned off as long as the temperature is above the threshold level and comparator is in its high output state. 
         [0034]    When the temperature drops back below the threshold level and the thermistor voltage drops below the reference level, the comparator will return to its low output state, thereby resetting the protection circuit and restoring operating current to optocouplers  34 ,  36 . 
         [0035]    As long as current is being delivered to the optocouplers from the DC supply, LED  53  will be illuminated to provide a visual indication that a control signal is being delivered to solid state switches  27   29 . 
         [0036]    Although the embodiment of  FIG. 1  is designed for use with three-phase power systems and loads, it can be utilized with single-phase systems and loads as well. In  FIGS. 2A   2 D, the relay is illustrated as having a housing  94  with input terminals  1 ,  3 ,  5  for the line connections, output terminals  2 ,  4 ,  6  for the load connections, and input terminals  96 ,  97  for the control signal. Circuits between input terminal  1  and output terminal  2 , input terminal  3  and output terminal  4 , and input terminal  3  and output terminal  6  are made and broken by contacts  12 ,  13 , and  14  and by solid state switches  27 ,  28 , and  29 , respectively. 
         [0037]      FIG. 2A  illustrates use of the relay with a standard 220 or 440 volt three-phase AC supply  98  and a three-phase load  99 , as in  FIG. 1 . In this embodiment, line conductors L 1 , L 2 , and L 3  are connected to input terminals  1 ,  3 , and  5 , and the load is connected to output terminals  2 ,  4 , and  6 . The hybrid relay can also be used in a four-wire, three-phase system, if desired. 
         [0038]    In  FIG. 2B , the relay is illustrated in connection with a 120 or 240 volt single-phase AC source  101  and a single-phase load  102 . In this embodiment, neutral conductor N is connected to input terminal  1 , line conductor L 1  is connected to input terminal  3 , the load is connected to output terminals  2  and  4 , and no connections are made to input terminal  5  and output terminal  6 . 
         [0039]      FIG. 2C  illustrates use of the relay with a 120 or 240 volt single-phase AC source  106  and two single-phase loads  107 ,  108 , where the total load current is less than the output rating of the relay. In this embodiment, neutral conductor N is connected to input terminal  1 , line conductor L 1  is connected to input terminals  3  and  5 , load  107  is connected to output terminals  2  and  4 , and load  108  is connected to output terminals  4  and  6 . 
         [0040]    In  FIG. 2D , use of the relay is illustrated in connection with a 120 or 240 volt single-phase AC source  111  and two single-phase loads  112 ,  113 , where the total load current is greater than the output rating of the relay. In this embodiment, neutral conductor N is connected to input terminal  1  and to a hard-wired return leg  114 , line conductor L 1  is connected to input terminals  3  and  5 , load  112  is connected to output terminal  4  and to return leg  114 , and load  113  is connected to output terminal  6  and to return leg  114 . 
         [0041]    The solid state switches and associated circuitry can be constructed in a single package with the EMR contacts and operating coil, or they can be constructed as a separate unit for use with existing EMRs or contactors.  FIGS. 3   5  illustrate an embodiment of the latter type in which the solid state switch is constructed in the form of a separate module  116  which is mounted on and connected to a conventional dedicated purpose contactor  117 . 
         [0042]    The contactor has a generally rectangular housing  119  in which the electromagnetically operated contacts and operating coil are enclosed, with terminals  121 ,  122 ,  123  on one side of the housing for connecting supply conductors L 1 , L 2 , L 3  to the contacts, with screws  124  for securing the conductors to the terminals. Output terminals  126 ,  127 ,  128  are located on the opposite side of the housing for connecting the load to the contacts, with screws  129  for securing the load conductors to the terminals. Operating coil terminals  131 ,  132  extend from the housing below terminals  121 ,  122 ,  123  for connection to supply lines for energizing the coil. 
         [0043]    Switch module  116  has a generally rectangular housing  133  that rests on the upper wall of the contactor housing, with depending flanges  134  that overlie the upper portions of the end walls of the contactor housing to hold the module in place. Flat leads  136 ,  137 ,  138  and  141 ,  142 ,  143  are connected respectively to the line and load terminals of the solid state switching devices within the housing and extend in a downward direction in alignment with the corresponding terminals of the contactor. The lower portions of these leads are bent outwardly for engagement with the contactor terminals, and they are secured to the terminals by screws  124 ,  129 . 
         [0044]    Output terminals  146 ,  147  for the AC switch within the module are provided on the upperwall of housing  133  and are connected to coil terminals  131 ,  132  by wire leads  148 ,  149 . At one end, these leads have loop lugs  151  which are secured to terminals  146 ,  147  by screws  153 . At the other end, the leads have spade lugs  152  which are secured to terminals  131 ,  132  by screws  154 . An MOV  156  is also connected to terminals  131 ,  132  to provide overvoltage protection when the coil is energized and the solid state switching device is receiving its control signal 
         [0045]    Input terminals  157 ,  158  are also provided on the upper wall of housing  133  for the control signals that open and close the AC switch within the housing. 
         [0046]    While the solid state relay module is illustrated as being mounted on top of the contactor in this particular embodiment, it will be understood that the solid state module can equally well be mounted to the side, below, or inside a dedicated purpose contactor, depending upon the application in which it is to be used. 
         [0047]    The invention has a number of important features and advantages. It provides a cost effective means of addressing the known limitations of both solid state relays and electromechanical relays, and by combining solid state switching with electromechanical switching, it provides a reliable hybrid power relay with no arcing or transient disturbances when the relay contacts open and close, and it provides the proper timing between the opening and closing of the solid state switching devices and the mechanical relay contacts without complicated control circuits or a computer. It can be used in both single-phase and three-phase system, it allows the large alternating currents to be controlled with a low voltage DC control signal, and it protects the solid state components from overheating without unwieldy heat sinks. 
         [0048]    The solid state switching provides a nearly unlimited life expectancy with zero transients during make and break transitions, while the electromechanical relay contacts eliminate nearly all of the thermal heating associated with solid state relays during load current conduction, thus providing a contactor with superior performance. 
         [0049]    The solid state and electromechanical sections can be constructed as an integral package, or the solid state switches and associated circuitry can be constructed in the form of a separate module that can be used with existing contactors or relays. It can, for example, be constructed in a housing that mounts on the housing of a commercially available dedicated purpose contactor, with leads that connect directly to the terminals of the contactor and are secured to the terminals by the same screws that connect the supply lines and load to the contactor. 
         [0050]    It is apparent from the foregoing that a new and improved hybrid power relay has been provided. While only certain presently preferred embodiments have been described in detail, as will be apparent to those familiar with the art, certain changes and modifications can be made without departing from the scope of the invention as defined by the following claims.