Abstract:
A control system for controlling and synchronizing a plurality of medium-voltage vacuum contactors comprises a two-level network structure. A dedicated network includes a plurality of servant control units operably coupled to the vacuum contactors and configured to ascertain a plurality of different data and conditions thereof. In addition, the dedicated network includes a master control unit in serial communication with the servant control units and configured to send and receive communications therewith. The master control unit is operably coupled to a control network including a plurality of various control devices. The master control unit is configured to send predetermined data received from the servant control units to the control network. The two-level network structure enables relatively jitter free communication on the dedicated network while not overwhelming the control network with unnecessary data. The system is further configured to diagnose and prevent a variety of different vacuum contactor failures.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   N/A 
   CROSS REFERENCE TO RELATED APPLICATION 
   N/A 
   BACKGROUND OF THE INVENTION 
   The present invention relates generally to medium-voltage vacuum contactors and in particular to control systems for controlling and synchronizing multiple vacuum contactors. 
   A vacuum contactor generally comprises three interrupters or vacuum bottles operated by an electromagnet assembly through a mechanical linkage. Such vacuum contactors are resistant to a variety of adverse atmospheric conditions and have relatively long electrical and mechanical lives. Each interrupter consists of two contacts enclosed in a ceramic housing or metal bellows. An upper contact is mounted to a fixed shaft and the lower contact is mounted to a moveable shaft. Each contactor is in communication with a control module adapted to open and close the contacts of the contactors. Medium voltage vacuum contactors are designed to operate in the 2400-7200 volt range and may be used with all types of Alternating Current (AC), loads including, for example, three-phase motors, transformers, power capacitors and resistive heating loads. 
   Vacuum contactors oftentimes include microprocessor “controllers” in communication therewith and configured to allow the contactors to be controlled, for example, from remote locations by digital signals sent along a control network. Typically, these control networks are low-level control networks such as, for example, DEVICENET, having a limited number of nodes being based on the Controller Area Network (CAN) standard. For this reason, communication between a control system and the vacuum contactor controllers is normally limited to simple on and off commands. The timing sequence may be controlled by a Programmable Logic Controller (PLC). 
   Control systems for electrical switching devices such as contactors are generally known in the art. For example, systems such as those disclosed in U.S. Pat. Nos. 5,506,485 to Mueller et al. and 5,610,579 to Early et al. disclose control systems for electrical switching devices. Typically, the control networks communicating between the PLC are low-level control networks such as DEVICENET providing simple interface circuitry but being able to connect only a limited number of nodes being based on the CAN standard (originally intended for automotive use). DEVICENET communication between a control system and the vacuum contactor controllers is suitable for simple on and off commands. However, the aforementioned systems are adapted for use with relatively low-voltage switching devices. Accordingly, a system for operating relatively higher voltage switching devices is desired. 
   In the control of medium voltage motors and the like it may be desirable to provide for high-speed synchronization of multiple vacuum contactors or other operations that require high speed communication. Such high speed communication could be possible through higher speed control networks such as CONTROLNET or ETHERNETIP, but these networks require considerable interface circuitry and sophisticated interconnecting media that would be prohibitively expensive on individual vacuum contactor controllers. 
   SUMMARY OF THE INVENTION 
   The present inventors have recognized that more sophisticated monitoring of the vacuum contactor controllers may be performed by generating a two-level network having a local dedicated network allowing high-speed communication of real-time operating data from the vacuum contactor controllers to a master module which may then use this data directly for coordination of the vacuum controllers or to abstract important information for forwarding to a PLC or the like on a low-speed network. The present invention allows valuable real-time information about contactor operation to be collected while still allowing the contactors to be controlled with a simple low-speed control network. The real-time data offers the possibility of a variety of improved functions. For example, such data allows for the prediction of contact failure, anti-kiss and anti-pumping protection features. 
   Specifically, the present invention provides a vacuum contactor system for use in an industrial control system having a plurality of vacuum contactors. The system further comprises a plurality of servant control units associated with each one of the vacuum contactors. Each of the servant control units includes a processor, memory module, and at least one sensor adapted to monitor operation of the associated vacuum contactor to provide real-time operating data of the vacuum contactor. The system further comprises a dedicated network connecting the plurality of servant control units for communication therebetween. The dedicated network, however, is not connected with the other devices in the industrial control system. The system also comprises a control network configured to communicate with the other devices in the industrial control system. Further, a master control unit having a processor and memory module is provided to communicate with the dedicated network and control network thereby exchanging data therebetween. The servant control units and master unit are configured to execute a stored program so that the servant control units may communicate the real-time operating data to the master control for coordination of all of the vacuum contactors by the master control unit. 
   It is thus one object of the present invention to permit high speed exchange of real-time operating data for coordination of vacuum contactors without overwhelming low bandwidth low-level control networks. 
   The master control unit of the present invention may be configured to control the vacuum contactors. 
   It is thus another object of the present invention to allow cost-effective local control of all of the vacuum contactors by using one vacuum contactor controller as the master controller thereby eliminating the need for a dedicated master controller. It is a further object of the invention to allow communication with the control system for a single vacuum contactor by using a master control module. 
   The master control unit may further be adapted to communicate real-time data with an industrial control system. 
   It is thus another object of the present invention to provide the benefits of selected real-time data to the control system without overwhelming the low-level control network. 
   The master control unit may further provide anti-kiss functionality that ensures that the contacts of the vacuum contactors are closed and sealed prior to being opened. 
   It is thus another object of the present invention to provide improved protection of the vacuum contactors that maybe coordinated from a master location. 
   The master control unit may further provide anti-pumping protection functionality wherein the master control unit prevents the contacts of the vacuum contactors from rapidly opening and closing. 
   It is thus another object of the present invention to provide improved protection for the contacts of the vacuum contactors by coordinating their operation from a master location. 
   The master control unit of the present invention may further provide a failure prediction of the individual contacts of each of the vacuum contactors. 
   It is thus yet another object of the invention to allow predictive monitoring of failures of vacuum contactors that may be communicated to the control system. 
   The communication protocol of the present invention may be configured to provide a fixed time slot for each vacuum contactor. 
   It is thus another object of the present invention to provide a predictable communication protocol to prevent loss of network data. 
   The communication protocol of the present invention may further transmit scheduled and unscheduled communications from the master control unit to the servant control units and from the servant control units to the master control unit. 
   It is thus yet another object of the present invention to provide a communication protocol capable of communicating both primary data on a continuous basis as well as secondary data on an as-needed basis while managing network traffic. 
   The control system of the present invention may further be configured to communicate a variety of different data including line voltages, coil current, Cyclic Redundancy Check (CRC), and warning messages. 
   It is yet another object of the present invention to provide continuous monitoring of vacuum contactor data. 
   The dedicated network of the present invention is configured to provide direct communications to the slave modules thereby bypassing the latency that would be inherent in using the control network. 
   It is thus an object of the present invention to allow for relatively fast communication between the devices of the dedicated network while not overwhelming the bandwidth of the control network. 
   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 
       FIG. 1  is a cross-sectional view of a vacuum contactor used with the present invention; 
       FIG. 2  is a schematic diagram of the dedicated network of the control system of the present invention communicating between a master and multiple servant control units; 
       FIG. 3A  is a diagram of the message structure of a communication from the master control unit of the present invention to a servant control unit of the present invention; 
       FIG. 3B  is a diagram of the message structure of a communication from the servant control unit of the present invention to a master control unit of the present invention; 
       FIG. 4  is a diagram depicting a transmission cycle of the control system of the present invention; 
       FIG. 5  is a flow chart showing the contact closure failure detection process of the control system of the present invention; 
       FIG. 6  is a flow chart illustrating the anti-kiss functionality of the control system of the present invention; and 
       FIG. 7  is a flow chart depicting the anti-pumping functionality of the control system of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring initially to  FIG. 1 , a vacuum contactor system  10  includes a vacuum contactor  12  and a vacuum contactor controller  14 . 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 . 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). 
   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. Raising the armature  24  also opens a normally closed auxiliary contact  30  outside the vacuum bottle  15 . 
   Turning now to  FIG. 2 , the industrial control system  40  of the present invention includes a PLC  42  in communication with a control network  44  and a master control unit  46 . The control network  44  typically includes a plurality of other devices attached thereto. The master control unit  46  is in communication with a dedicated network  48  and includes a processor and a memory module for communicating therewith. 
   Control network  44  is typically used to interconnect various control devices for data exchange. Further, control network  44  is generally a relatively simple and slow network and typically comprises a baudrate in the range of 125 kbits/s and 500 kbits/s. Control network  44  is preferably DEVICENET. 
   The dedicated network  48  comprises a plurality of servant control units  50  connected to one another for communication therebetween. The information communicated between master control unit  46  and the servant control units  50  may be both predetermined and user defined. In addition, the dedicated network  48  is not in communication with the other devices of the industrial control system  40 . 
   Further, dedicated network  48  typically comprises a plurality of Recommended Standard 485 (RS-485) serial connections. Communication across the RS-485 serial connections allows for relatively fast communication on the dedicated network. By separating the dedicated network  48  from the control network  44 , a large amount of relatively fast communications may take place on a dedicated network  48  without overwhelming the relatively slow control network  44 . The use of a RS-485 interface rather than a Recommended Standard 232 (RS-232) interface allows the master control unit  46  to communicate with up to six servant control units  50  whereas the use of a RS-232 interface would limit the master control unit  46  to communication with two servant control units  50 . 
   The communications carried out over the RS-485 serial interface between the master  46  and the individual servant control units  50  will be carried out at a periodic, predetermined rate such as, for example, every 10 ms. Servant control units  50  are configured to send a variety of different real-time data to the master  46  such as, for example, input line voltage, main DC bus voltage, vacuum contactor coil current feedback, user inputted commands, Dual in-line Package (DIP) switch settings, fault/status/warning messages, and any other such data as may be deemed necessary in the practice of the control system  40  of the present invention. Likewise, the master  46  also sends a variety of data over the RS-485 serial interface to the servant control units  50  such as various control commands, coil current control, drop-out time, time delay under-voltage ride through (TDUV) time, jump to bootcode commands, learn mode commands, and other such commands as may be deemed necessary. 
   Each of the servant control units  50  is coupled to a vacuum contactor  12  for communication therewith. Servant control units  50  include a processor, memory module, and at least one sensor adapted to monitor operation of the associated vacuum contactor  12  to receive real-time operating data of the vacuum contactor. Further, servant control units  50  are configured to execute a stored program that is configured to communicate the real-time operating data to the master control unit  46  for coordination of all of the vacuum contactors  12  by the master control unit  46 . In addition, the communication between the servant control units  50  and the master control unit  46  is synchronized so as to ensure that the contactors  12  of the present invention work in unison. 
   The master control unit  46  may be configured to communicate certain real-time data received from servant control units  50  to the industrial control system  40  of the present invention. Accordingly, by providing a dedicated network  48  for the exchange of real-time data between servant control units  50  to monitor the vacuum contactors  12 , the system of the present invention is capable of communicating necessary information to the control system  40  through the master control unit  46  without overburdening the control system  40  with all of the real-time data exchanged between servant control units  50  and master control unit  46 . As such, only that real-time information required by the control system  40  is communicated from the master control unit  46  through PLC  42  to the control system  40 . 
   The communication between the servant control units  50  and the master control unit  46  allows for the monitoring of the vacuum contactors  12  associated with servant control units  50 . For example, the mechanical and electrical condition of the vacuum contactors  12  may be communicated from each of the servant control units  50  to the master unit  46 . Accordingly, the master unit  46  may communicate that information by way of, for example, a Personal Digital Assistant (PDA) interface or other such communication device to a user thereby allowing for the performance of preventive maintenance of the vacuum contactors  12 . 
   Turning now to  FIGS. 3A and 3B , a diagram depicting the data packet message structure for the dedicated network  48  of the present invention is shown. First turning to  FIG. 3A , a data structure  60  depicting communications from the master control unit  46  to the servant control units  50  is illustrated. Data structure  60  includes a destination address  61 , an Unscheduled Command  62 , Control Command  63 , Coil Current Command High Byte  64 , Coil Current Command Low Byte  65 , Coil Drop Out Time Command High Byte  66 , Coil Drop Out Time Command Low Byte  67 , and Servant Control Unit Jump to Bootcode Command  68 , CRC High Byte  69 , and CRC Low Byte  70 . 
   Unscheduled command  62  and unscheduled response  73  comprise the sending and receiving by the master control unit  46  and servant control units  50  of secondary operations data. Unscheduled commands and responses are typically only sent on the first transmission cycle as most of the data transmitted between the master control unit  46  and servant control units  50  are required on a continuous basis. 
   Control command  63  comprises a command input for opening and closing the contactors of the various vacuum contactors  12  of the control system  40 . Further, control commands  63  serve as status relays for indicating contactor and control unit status. 
   Coil Current commands  64 ,  65  represent the levels of the contactor coil currents of the contactors  12  of the present system  40 . Coil drop out time  66 ,  67  represents the time in millisecond increments between when an open command is given and the time when the contactor should drop out. 
   Servant jump to bootcode  68  is a command sent to prompt the servant control unit  50  to which the message is directed to jump to its bootcode thereby allowing for reprogramming of that particular servant  50 . Preferably, the system  40  of the present invention will only allow for the command to be issued if a particular servant is currently not powering its own contactor coil. If the servant  50  is actually powering the contactor coils when the message is received, the servant  50  simply ignores the message. 
   CRC  69 ,  70  represents a message containing, for example, a checksum value from which the integrity of data may be determined by checking against this received value and a real time calculated value. 
   Referring now specifically to  FIG. 3B , data structure  71  illustrates the servant control unit  50  to master control unit  46  message data structure. Data structure  71  includes the Address of the servant control unit  72 , Unscheduled Response  73 , Input Line Voltage High Byte  74 , Input Line Voltage Low Byte  75 , Main Direct Current (DC) Bus Voltage High Byte  76 , Main DC Bus Voltage Low Byte  77 , Vacuum Contactor Coil Current High Byte  78 , Vacuum Contactor Coil Current Low Byte  79 , User Input Command  80 , DIP Switch Inputs  81 - 84 , Faults/Warnings High Byte  85 , Faults/Warnings Low Byte  86 , CRC High Byte  87 , and CRC Low Byte  88 . 
   Input line voltage  74 ,  75  represents the root mean square (“RMS”) value for the input line voltage. Main DC Bus Voltage  76 ,  77  represents the level of the DC bus voltage. Vacuum contactor coil current  78 ,  79  represents the real-time level of the contactor coil currents. 
   User input  80  contains bits that represent the status of the OPEN, CLOSE, and AUX inputs as well as the status of the MODULE/CONTACTOR status relays for the servant control units  50 . 
   DIP Switch settings  81 ,  82 ,  83 , and  84  contain information regarding the positions of various DIP switches on the network. 
   Faults and warnings  85 ,  86  represent various messages that may be communicated from the servants  50  to the masters  46 . For example, invalid command, mechanical latch failures, contactor pick-up failures, contactor drop-outs, long drop-out times, and other such warnings may be communicated to the masters  46 . Finally, CRC  87 ,  88  represent a message containing, for example, a checksum value from which the integrity of data may be determined by checking this value against a real time calculated value. 
   An important function of the message structure utilized by the present invention is that the length of each of the messages remains constant and thus it is perfectly predictable as to how often messages will occur, thereby ensuring that uncertainty in message delay or jitter is nearly nonexistent. This is especially important because if there is a lot of network jitter, operation of the system will be highly sporadic and therefore making operation thereof substantially unreliable. 
   Now turning to  FIG. 4 , a single transmission cycle  90  between the master  46  and the control units comprises a first communication  92  between the master and a first servant control unit  50 . First communication  92  comprises a first master-servant message  94  and a first servant-master response  96 . Overall, first communication  92  preferably takes about 100 microseconds. Each of messages  94  and  96  further includes a time out after 1 ms after which the sender of the initial transmission is required to resend the communication if a response thereto is not received. Preferably, the first master-servant message  94  comprises 8 bytes of data whereas the servant-master response comprises a 12 byte communication. The transmission cycle  90  is complete upon the communication of the master  46  with each of the units  50  on the dedicated network  48 . As shown in  FIG. 4 , the transmission cycle further includes a second communication  98 , a third communication (not shown), a fourth communication (not shown) and a fifth communication  104 , wherein each of the communications is structured similarly to the first communication  92  having a master-servant message and servant-master response. 
   It should be understood that each of the various communications from the master  46  to the servant control units  50  of transmission cycle  90  are actually communicated to all of the control units, however, each transmission from the master  46  is coded such that only the intended receiver of the communication responds. 
   Turning now to  FIG. 5 , a method for detecting contact closure failure in a vacuum contactor  106  including a measuring step  107  wherein the servant control units  50  measure the actual time required for the contactor to close. Next, a transmission step  108  includes the transmission of the measured time value as an unscheduled transmission to the master control unit  46 . If the time measured during the measuring step  107  exceeds a predetermined value, preferably about 150 ms, then the master control unit  46  indicates a fault during a decision step  109 . If the predetermined value is not exceeded, the process  106  is exited. 
   Now turning to  FIG. 6 , the control system  40  of the present invention includes an anti-kiss protection feature  110  that ensures that the main contacts of the vacuum contactors  12  are closed and sealed before they are allowed to open. The anti-kiss protection feature  110  is designed to ensure that once a contactor has been commanded to be closed, the contactor cannot be commanded to open until the closing process has been completed. Anti-kiss protection feature  110  includes a first step  112  a command to open the contacts of one of the vacuum contactors  12  is received by the master  46 . Next, the servant control unit  50  associated with the vacuum contactor  12  senses the current status of the contact in a second step  114 . Once servant control unit  50  obtains the status of the contact, a third step  116  includes servant control unit  50  sending the status to master unit  46 . Finally, once the master unit  46  receives a message that the contacts are currently closed, the master  46  may issue a request to the servant control unit  50  associated with the contactor  12  to open the contacts as step four  118 . If, however, the contacts are currently open, the master  46  does not issue a request to open the contacts, and the anti-kiss procedure  110  is performed again. 
   Referring now to  FIG. 7 , the control system  40  of the present invention includes an anti-pumping protection feature  120  intended to prevent the contactor from rapidly opening and closing due to incorrect or faulty control circuitry, a faulty holding coil, faulty control electronics or the failure of the latch mechanism to properly engage. As such, the input control signal is required to open then close again before it is allowed to issue another close command. If the contactor receives a signal to close  122  a timer is started  124 . Upon the issuance of an open command  126 , if the system receives another close command  128  thereafter, the system determines whether a timeout value has been exceeded 130. If the timeout has been exceeded, then the contactor will close, however, if not, the close command is removed 132. Once the close command is removed, the contactor will not close again until another close command is issued. 
   It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims