Abstract:
A controller for a vacuum contactor or the like measures barometric pressure and provides a short impedance characterizing pulse to the coils of the vacuum contactor coils to assess proper operating conditions of the coils and to check for coil or sensor faults.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    -- 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    -- 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to electromagnetically controlled switches, such as relays and contactors, and in particular to an improved controller for vacuum contactors. 
         [0004]    Vacuum contactors are electrically controlled switches used for interrupting high power circuits. In a vacuum contactor, a pair of contacts are enclosed inside a vacuum-tight bottle. One of the contacts is fixed to an end of the bottle and the other contact may be moved by means of a bellows toward and away from the fixed contact under the influence of an electrical solenoid. The vacuum surrounding the contacts helps suppress an arc formed when a circuit is interrupted. 
         [0005]    “Electrically-held” vacuum contactors, as the name suggests, hold the contacts in a closed position by continuously applying a holding current applied to the electrical solenoid. Typically this holding current is much less than the current used to close or pull in the contacts when the switch is actuated. “Mechanically-latched” vacuum contactors hold the contacts in the closed position by a mechanical latch, eliminating the need for a holding current. A second solenoid releases the mechanical latch when it is desired to open the contacts. 
         [0006]    The bellows that allows movement of one of the contacts applies a biasing force on that contact that is a combination of the spring force required to flex the bellows and resist closure of the contacts and the force of atmospheric pressure across the bellows tending to move the contacts together. An external spring may be used to balance these forces with the contacts open. 
         [0007]    This balance of forces is upset if the vacuum contactor is moved to a different altitude having a different atmospheric pressure. For this reason, it is know to provide an external spring that is replaceable or adjustable according to the altitude. Alternatively, it is known to adjust the pull-in and/or holding current of the electrical solenoid to compensate for any force unbalance. This adjustment is performed by means of a table and a set of switches that may be set by the user. 
         [0008]    Larger vacuum bottle and contact sets may be used for greater power handling. These larger vacuum bottles require greater actuation forces that are normally accommodated by larger solenoid coils. These larger coils require different actuation currents and holding currents. 
         [0009]    Operation of a vacuum contactor is normally mediated by a contactor controller providing regulated control of the power applied to the vacuum contactor solenoids adjusted by the user for solenoid coil size and/or altitude. Configuration of the contactor controller for different vacuum contactors and altitudes is complex and time consuming. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a contactor controller that may automatically configure itself for a wide variety of vacuum contactor types and operating altitudes. At initialization, the contactor controller interrogates the electrical characteristics of the attached coils of the vacuum contactor using a short pulse. The pulse power is selected to be sufficient to distinguish the impedance of the coil without activating the coil. The results of these measurements are used to determine the proper operating conditions of the coil and, in particular, the necessary coil actuation power. A barometric pressure sensor also may be used to further automatically adjust the operating condition for altitude. This coil measurement may also be used for ongoing fault detection. 
         [0011]    Underpinning this invention is the inventor&#39;s recognition that even minor errors in the configuration of the contactor controller for a vacuum contactor can contribute to premature failure of the vacuum contactor by over stressing of the vacuum bottle. 
         [0012]    Specifically, the present invention provides an electronic controller for an electromagnetically controlled electrical switch. The controller includes a coil power source providing connection points to at least one coil of the switch, and a test circuit provides an electrical pulse to the coil and monitors electrical flow to the coil to differentiate between at least two sizes of coil. A coil power source controller receives an actuation signal to provide power to the coil through the coil power source, where the power to the coil is automatically selected according to the size of coil determined by the test circuit. 
         [0013]    It is thus a feature of one embodiment of the invention to provide a controller that automatically configures itself for a variety of different electromagnetically actuated switches. It is another feature of an embodiment of the invention to provide a controller that better tailors actuation currents to the coils of vacuum contactors to reduce premature failure of the vacuum bottles of such controllers that may be caused by excessive flexure of the vacuum bottles under excessive actuation force. 
         [0014]    The test circuit may differentiate between sizes of coils by monitoring current flow after a predetermined period of time under application of a pulse of known voltage to the coil. 
         [0015]    It is thus a feature of one embodiment of the invention to provide a simple method of distinguishing coil types using an inherent quality of the coil and that thus does not require a machine-readable labeling of the coils. 
         [0016]    The pulse of known voltage and predetermined time may be selected to prevent activation of the electromagnetically controlled electrical switch for the coil sizes. 
         [0017]    It is thus a feature of one embodiment of the invention that it provides a testing mechanism that provides discrimination among coil types without inadvertent activation of equipment or devices attached to the vacuum contactor. 
         [0018]    The electronic controller may further include a barometric pressure sensor and the coil power source controller may receive a pressure signal from the barometric sensor to provide power to the coil based on the barometric pressure. 
         [0019]    It is thus a feature of one embodiment of the invention to automate the adjustment of control current for each different coil type according to the altitude of the vacuum contactor, thereby allowing more accurate correction. 
         [0020]    The power to the coil may be adjusted with barometric pressures according to a function unique to the deduced coil type. 
         [0021]    It is thus a feature of one embodiment of the invention to permit sophisticated, empirically derived power adjustments unique to a particular coil, providing superior coil actuation. 
         [0022]    The coil power source controller may further detect a fault condition and generate a fault signal based on electrical flow to the coil. 
         [0023]    It is thus another feature of one embodiment of the invention to employ the same mechanism used to set coil power to provide an additional functionality of fault detection. 
         [0024]    A fault signal may be based on electrical flow to the coil under a predetermined value indicating a missing coil or electrical flow to the coil exceeding a predetermined amount indicating a shorted coil, or electrical flow to the coil exceeding a predetermined difference from current flow expected of known coils, indicating an unknown coil. Each of these conditions may be distinguished to the user. 
         [0025]    It is thus a feature of one embodiment of the invention to provide for multiple types of fault detection. 
         [0026]    The electronic controller may employ the controllable power source to deliver the electrical pulse to the coil. 
         [0027]    It is thus another feature of one embodiment of the invention to make use of existing hardware for the purpose of characterizing the coil configuration. By controlling the same power supply used to provide power to the activation solenoids, the need for separate test circuit and isolation is eliminated. 
         [0028]    These particular features and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a diagram showing the controller of the present invention as connected to a vacuum contactor, with the vacuum contactor in an open state; 
           [0030]      FIG. 2  is a fragmentary view of  FIG. 1  showing the vacuum contactor in a closed state and mechanically latched; 
           [0031]      FIG. 3  is a block diagram of the components of the controller of  FIG. 1  including a microcontroller independently controlling electrical power to coils of the vacuum contactor; 
           [0032]      FIG. 4  is a plot of electrical power applied to the coils of the vacuum contact during a test mode, showing voltage and possible current waveforms during a test pulse; and 
           [0033]      FIG. 5  is a flow chart of a program executed by the microcontroller of  FIG. 3  implementing the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Referring now to  FIG. 1 , a vacuum contactor system  10 , providing an example electromechanical switch system suitable for use with the present invention, includes a vacuum contactor  12  and a vacuum contactor controller  14 . 
         [0035]    As is generally understood in the art, the vacuum contactor  12  may include one or more vacuum bottles  15  providing a sealed evacuated chamber  16 . Within the chamber  16  are two contacts: a stationary contact  18  fixed with respect to the vacuum bottle  15 , and a movable contact  20  attached to the vacuum bottle  15  by means of a bellows  22 . 
         [0036]    The bellows  22  allows axial motion of the movable contact  20  toward and away from the stationary contact  18  under the influence of a pivoting armature  24  attached to the movable contact  20  through a biasing spring (not shown). 
         [0037]    The armature  24  is raised or lowered by attraction between an armature tab  26  and a pole of a first electromagnet  28 . In operation, the armature  24  is moved to a lowered position, separating the contacts  18  and  20 , under the urging of a biasing spring  29  and is moved to a raised position by the attraction of the tab  26  to the electromagnet  28  when the electromagnet is energized. A raising of the armature  24  also opens a normally closed auxiliary contact  30  outside the vacuum bottle  15 . 
         [0038]    Each of these assemblies of vacuum contactor  12  may be duplicated for multiphase circuits. For multiphase circuits, the several vacuum bottles may be actuated by a common armature  24 . 
         [0039]    In a mechanically latched vacuum contactor  12 , an optional armature latch assembly  32  may be added. The armature latch assembly  32  includes a pivoting armature latch  34  which, in a lowered state (as shown in  FIG. 1 ), allows free movement of the armature tab  26  toward the electromagnet  28  to close the contacts  18  and  20 . Referring now to  FIG. 2 , when the armature tab  26  is adjacent the pole piece of the electromagnet  28 , the armature latch  34  rises as pulled by spring  36  allowing a roller  38  to capture the armature tab  26  against the pole of the electromagnet  28 . The roller  38 , held by the spring  36  retains the armature  24  upward with contacts  18  and  20  and auxiliary contacts  30  open. In this latched position of  FIG. 2 , no power is required in electromagnet  28  to hold contacts  18  and  20  and auxiliary contacts  30  open. 
         [0040]    Release of the armature  24  from the mechanical latching, and opening of contacts  18  and  20  and closing auxiliary contacts  30  is effected by a release electromagnet  40  that, when activated, draws the armature latch  34  downward pulling roller  38  away from armature tab  26  and allowing the armature tab  26  to move away from electromagnet  28  as shown again in  FIG. 1 . 
         [0041]    Referring still to  FIG. 1 , a vacuum contactor  12  is normally connected to a vacuum contactor controller  14  which is connected to receive a switch signal from the auxiliary contacts  30  and which provides power leads to electromagnets  28  and  40  (for a mechanically latched vacuum contactor  12 ) and to electromagnet  28  only (for an electrically held vacuum contactor  12 ). The vacuum contactor controller  14  may also connect to one or more serial communication channels  42  and to one or more analog or digital input output (I/O) lines  44 . The vacuum contactor controller  14  may also connect to a barometric pressure sensor  46 . 
         [0042]    Referring now to  FIG. 3 , the vacuum contactor controller  14  may include a microcontroller  48  of a type well known in the art communicating with a nonvolatile memory  50  such as an EEPROM which may hold a stored program executing the steps of controlling the vacuum contactor as will be described below. 
         [0043]    Interface leads of the microcontroller  48  may be attached to network interface circuits  52  providing for the communication protocols of the serial communication channels  42 , for example, DeviceNet, CAN, or RS-232 or RS-485 protocols. Other interface leads of the microcontroller  48  may be attached to I/O circuitry  54  providing an interface to the I/O lines  44 . 
         [0044]    A digital input lead of the microcontroller  48  may receive the switching signal from the auxiliary contacts  30  through interface circuitry  56 . The electrical signal from the barometric pressure sensor  46  may be received by an internal analog to digital converter in the microcontroller  48 . 
         [0045]    The microcontroller  48  also provides output signals controlling coil power supplies  60  and  62 , the latter receiving conditioned power and providing pulse width modulated (PWM) DC to the coil of electromagnet  28  (and optionally the coil of release electromagnet  40 ), for example, through the use of an insulated gate bipolar transistor (IGBT) circuit of the type well known in the art. Additional coil power supplies  60  and  62  may be used in controllers controlling vacuum contactor with additional vacuum bottles  15 . Current sensors  64  on the output of the power supplies  62  and  60  allow for the measurement of current flow to the coils of electromagnet  28  and  40  by the microcontroller  48  through an internal A/D converter. 
         [0046]    The vacuum contactor controller  14  may receive electrical power, for example, 110-240 VAC or 110-250 VDC, which may be conditioned according to methods well known in the art to condition power for operation of these components. The power circuitry is not shown for clarity. In addition, the microcontroller  48  may also connect to panel displays having LEDs or the like for indicating status conditions of the vacuum contactor system  10 , for example, a fault condition or the presence or absence of electrical power. The panel displays are not shown but are of a type well known in the art. 
         [0047]    Referring now to  FIG. 5 , when the vacuum contactor controller  14  is initially powered up or after the vacuum contactor controller  14  has been reset, the controller begins execution of a stored program  84  held in memory  50  beginning at process block  66 . 
         [0048]    After the microcontroller  48  performs standard internal diagnostics, the microcontroller  48  reads and stores the barometric pressure from the barometric pressure sensor  46  as indicated by process block  68 . As mentioned above, this barometric pressure will affect the force required to close the contacts  18  and  20 . 
         [0049]    Next, at process block  70 , the microcontroller  48  checks the response of any coils attached to its terminals possibly including coils of electromagnet  28  and  40 . Referring also to  FIG. 4 , the checking of coils response may be done by applying a test voltage pulse  72  on each terminal set possibly connected to a coil, using power supply  60  and  62 . The voltage pulse  72  will have a predetermined voltage V 0  and period of time  74  selected to contain insufficient energy to activate any known coil of electromagnet  28  or  40 . 
         [0050]    Nevertheless, the voltage V 0  of the test voltage pulse  72  will induce a current  78  in any coil of electromagnet  28  or  40  attached to the particular terminals of the microcontroller  48 , and this current  78  will rise over time depending on the impendence of the attached coil of electromagnet  28  or  40 . At the conclusion of time  74 , the peak current  78  is sampled through current sensors  64  and evaluated per decision block  76  against thresholds I 0 -I 3  stored in the memory  50 . 
         [0051]    I 0  is the lowest threshold, and a sampled current at or below I 0  indicates that no coil is attached to the particular terminals or else that the coil is open. An internal configuration file in memory  50  (set by the user) is reviewed to see if the vacuum contactor  12  is electrically held or mechanically latched. If the vacuum contactor  12  is electrically held and the terminals exhibiting an open circuit are designated for a coil of release electromagnet  40 , no fault is indicated at decision block  76  and the program proceeds to process block  82 . Otherwise, if the vacuum contactor  12  is mechanically latched and the terminals exhibiting an open circuit are designated for a coil of release electromagnet  40 , or if the vacuum contactor  12  is electrically held and the terminals exhibiting an open circuit are designated for a coil of actuation electromagnet  28 , a fault is indicated and a fault condition is generated for the user as indicated by decision block  76  of  FIG. 5 . In an alternative embodiment, no internal configuration file is used, and the controller assumes that the vacuum contactor  12  is electrically held if there is a high impedance at all terminals designated for coils of release electromagnets  40 . 
         [0052]    If the sampled current is between I 0  and I 1 , for example, it may be deduced that a coil is present at the terminals having a first impedance, for example, indicating an 800 ampere coil used for high current vacuum contactors. Alternatively this second range may be a window centered on a current I 1  admitting the possibility of currents outside of this window and other windows generating a fault as being an unknown coiled type. 
         [0053]    If the sampled current is between I 1  and I 2 , for example, it may be deduced that a coil is present at the terminals having a second impedance, for example, indicating a 400 ampere coil used for low current vacuum contactors. Alternatively this second range may be a window centered on a current I 2 , generating a fault if the current is within no other window. 
         [0054]    Finally, a high threshold I 3  is established such as is used to indicate a short circuit across the terminals (and hence a shorted coil) if the current exceeds this amount. A fault is also generated in this situation. 
         [0055]    I 4  represents a current level necessary to activate the coil when applied in sufficient duration and is not exceeded for normal coils of electromagnet  28  or  40 . 
         [0056]    At decision block  76 , the output of the barometric pressure sensor  46  may also be evaluated to see if it outside an expected range of values that would indicate a fault in the barometric pressure sensor  46  or an invalid altitude (being an altitude outside of the correction and/or operating range of the system). In such cases, a fault signal indicating failure of the barometric pressure sensor  46  is generated. 
         [0057]    As indicated by decision block  76  any of these fault conditions may result in an output signal that may be used to notify the user of the fault and type of fault as indicated by process block  80 . This fault signal may be in the form of one or more indicator lights on the front panel of the vacuum contactor controller  14  or a signal transmitted over one of the serial communication channels  42  to a central controller or the like. 
         [0058]    If there is no fault condition at decision block  76 , then at process block  82  a steady-state current to be provided to the coils of electromagnet  28  (and  40 ) when they are to be activated, may be determined. Referring to  FIGS. 3 and 6 , this process of determining the operating current for a coil of electromagnet  28  may employ a lookup table  85  held in memory  50  and storing a set of empirically derived current values  86  necessary to “pull-in” and “hold” the armature  24  with coil of electromagnet  28  at different barometric pressures. Typically, for example, the pull-in current will be substantially higher than the holding current. 
         [0059]    Based on the previously stored barometric pressure and the coil type deduced from the test pulse  72  described above, current values  86  are identified and stored to be used for operation of the coil of electromagnet  28 . When the vacuum contactor controller  14  receives an actuation signal, for example, through I/O lines  44  or serial communication channels  42 , the microcontroller  48  will control the appropriate coil&#39;s power supply  60  or  62  to output an average PWM voltage to the appropriate coil to produce the current value from this table  85 . If the vacuum contactor is mechanically latched, only the pull-in current for coil of electromagnet  28  is needed and the holding current may be the pull-in current to be used for coil of release electromagnet  40 . Generally the current needed for coil of release electromagnet  40  does not change with changes in barometric pressure. 
         [0060]    Referring again to  FIG. 5 , periodically during operation of the contactor system  10 , the coil response may be checked per process block  70 , principally to determine if the coils have faulted or shorted during periods of inactivity. In this way the electrical integrity of the vacuum contactors  12  may be better ensured against times when a circuit interruption is required. Failure of this periodic check results in a fault condition being generated. 
         [0061]    The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.