Abstract:
A universal control and diagnostic system for a transformer that may be retrofit with existing control and tap-changer equipment, the system providing for remote monitoring and control of the equipment and for measuring various criteria associated with the tap-changer to substantially minimize damage to the equipment during a maneuver and for substantially avoiding carbonization of a connected contact.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a control system for a transformer or reactor and means for carrying out diagnostics of a tap-changer and methods for carrying out such diagnostics. 
     BACKGROUND OF THE INVENTION 
     Control systems for monitoring and changing of tap settings on transformers have been utilized with varying levels of success and efficiency. Historically, control systems did not provide for the sophisticated levels of control and monitoring that are highly desirable by means of network connections. 
     There are relatively large numbers of control cabinets and installations where the control system, while electronic in nature, is not compatible with current networking and communications technology. It is desirable to convert many of the existing control system over to a format that may easily be controlled and monitored remotely over, for example, a network. However, a problem involved with this conversion is that the costs involved with removing the control system and cabinet of the existing system and fully replacing it with an updated electronic system are correspondingly high, both in terms of materials and labor. 
     For example, control systems for changing of tap settings of a transformer comprise a relatively large amount of input and output signals, both for electronic control and electronic monitoring. These signals however, are generated having a particular format, voltage level, current, etc. To replace the equipment so that a desired signal format can be generated is impractical and extremely costly. 
     It is also critical that during operation of the tap-changer, that the operation of the tap-changer be monitored so that catastrophic failure is avoided. In relatively large commercial applications, the heat build up that may occur in a tap-changer due to, for example, incomplete switch over or change of a tap setting, can quickly lead to a catastrophic failure of the transformer. This could present a danger to individuals as well as be quite costly both in terms of replacement cost for the transformer and associated equipment, and downtime for customers. 
     Therefore, an effective monitoring system is critical to the safe functioning of these systems. However, the monitoring systems of many current tap-changers do not lend themselves well to being integrated with a networked control system. The numerous formats of the control and monitoring signals in existing installations further compound the challenge. 
     Still another challenge facing tap-changing systems is that, even during normal use of the transformer, the various contacts in the tap-changer will wear over time as current is switched by the tap-changer. For example, over time, the contacts for the tap-changer can carbonize, or develop carbon deposits on the surface of the contacts. This is highly disadvantageous because carbon deposits tend to insulate or increase the resistance to the flow of current. With the relatively high voltages typically used for commercial applications, heating and also arcing will occur at these higher resistance locations. The arcing in turn generates very high heat depositing still more carbon on the surface of the contact. If ignored, overheating and arcing due to the poor contact can lead to catastrophic failure of the device may occur. 
     Accordingly, what is desired is a control system that has the versatility to be integrated and/or retrofitted with existing control signal formats and simultaneously may be integrated with a networked control and monitoring system. 
     It is further desired to provide a networked control system and method that may effectively be used with existing tap-changing systems to monitor the changing of tap settings and for entering an alarm condition when preset limits are exceeded. 
     It is still further desired to provide a networked diagnostic control system and method that may be integrated with existing tap-changing system that will substantially minimum or even prevent carbonization of the tap-changer. 
     SUMMARY OF THE INVENTION 
     These and other objects are achieved in one advantageous embodiment by the provision of a networked electronic control system that may be fully integrated with an existing transformer/reactor into an existing control cabinet. 
     An integrated electronic control and monitoring system according to a first advantageous embodiment of the invention, may comprise an electronic board rack including, a main processor board and various peripheral boards. It is contemplated that the boards may be configured to handle both analog and digital input/output signals of various types and formats so that these may be directly coupled to the electronic control system. This provides the advantage that it is possible to combine and exchange boards of all types in the rack. Further each signal may be configured individually at any channel on each board. 
     Various control and/or monitoring signals are sent and received, via, for example, an interface converter from TCP/IP over serial communication to Ethernet working in both directions. In this manner, it is possible, for example, to make all cooling control configurations from remote locations. Start/Stop temperatures for each cooler group may further be set individually. Still further, groups can be included and/or excluded from the more advanced cooling control, while temperatures settings for advanced cooling control can be adjusted. 
     For monitoring purposes, data collecting from electronic control systems may be accomplished by an OPC (Object-linking and embedding for Process Control) server. Additionally, an alarm and trip limits for protection sensor can be remotely set on an individual basis. 
     The networked system, further allows for support for sensors that communicates via CAN (Control Area Network) bus, e.g. Hydran, where the CAN sensors may be configured directly in the electronic control system. When voltage measurement is connected to the transformer electronic control system, it is possible to regulate voltage with LTC via bus communication. 
     Also provided is a system and method that may be integrated with existing equipment, for monitoring and notifying a user of a malfunction after, for example, a tap-changer operation. 
     During a tap-changer operation, when the tap-changer is switching from one set of contacts to another, there typically will be arcs and current by-passes through resistors. If the change-over is not completed, additional arcing and current through the resistors can occur. This may cause a sudden spiking of the temperature in the equipment cabinet that, for example, an installed monitoring system may not be able to draw a conclusion on rapidly enough to prevent damage to the equipment. Accordingly, the installed control system may, in another advantageous embodiment, send out an alarm and may even trip the transformer if preset threshold values are exceeded. 
     To accomplish this, a first temperature measurement is obtained and stored that comprises an actual temperature measured in the tap-changer at the time for the switching operation. A second calculated temperature taking into consideration various criteria related to the tap-changing operation is further obtained and stored. These two temperatures will be used as references for additional temperature measurements taken for a period of time in the tap-changer after the switching operation. It is advantageous to measure temperature in the tap-changer up to, for example, five minutes after the switching operation. 
     It is advantageous to use the second calculated temperature to compensate for multiple operations of the tap-changer, which may generate additional heating. If however, the temperature increase in the tap-changer exceeds preset increase values, the system may alarm at a first lower threshold level, and may further trip at a second higher threshold level. 
     Further, a system and method are provided that may be integrated with existing equipment, for monitoring transformer/reactor operation and tap-changer operation to substantially prevent tap-changer carbonization. For example, if a tap-changer is placed on one contact for an extended period of time, the possibility of contact carbonization substantially increases. Once carbonization begins, the contacts are being damaged, therefore, one object for the diagnostic method is to substantially avoid carbonization. 
     Accordingly, it is contemplated that a contact should only be maintained in a particular position for a recommended connection time to avoid development of carbonization. Therefore, the amount of time that a particular contact has been in one position is measured and compared to the recommended connection time. When the measured time in one position has reached the recommended connection time, a warning system will communicate to the customer that it is time for exercising the tap-changer. 
     It is further contemplated that the recommended connection time may be variously calculated. For example, the measured temperature in the tap-changer will influence the recommended connection time as will the measured current passing through the contact. It is contemplated that the higher the temperature and the higher the current, the shorted the recommended connection time will become. Alternatively, the lower the measured temperature and the lower the measured current, the longer the recommended connection time will become. 
     It should be noted that the recommended connection time may be different, for example, in the fine and course selectors. It is still further contemplated that it may be desirable to take into consideration the previous contact position and/or positions of the contact in determining a recommendation for exercising the tap-changer. 
     It is important that the system knows particular tap-changer design as movement of contacts is dependent on that. For some tap-changer types, a change in the tap-changer position is not enough to move a fine contact from one position to another; sometimes two operations in the same direction are needed. To move the course (change-over) selector, sometimes a large amount of operations in one direction is needed. 
     For this application the following terms and definitions shall apply: 
     The term “data” as used herein means any indicia, signals, marks, symbols, domains, symbol sets, representations, and any other physical form or forms representing information, whether permanent or temporary, whether visible, audible, acoustic, electric, magnetic, electromagnetic or otherwise manifested. The term “data” as used to represent predetermined information in one physical form shall be deemed to encompass any and all representations of the same predetermined information in a different physical form or forms. 
     The term “network” as used herein includes both networks and internetworks of all kinds, including the Internet, and is not limited to any particular network or inter-network. 
     The terms “first” and “second” are used to distinguish one element, set, data, object or thing from another, and are not used to designate relative position or arrangement in time. 
     The terms “coupled”, “coupled to”, and “coupled with” as used herein each mean a relationship between or among two or more devices, apparatus, files, programs, media, components, networks, systems, subsystems, and/or means, constituting any one or more of (a) a connection, whether direct or through one or more other devices, apparatus, files, programs, media, components, networks, systems, subsystems, or means, (b) a communications relationship, whether direct or through one or more other devices, apparatus, files, programs, media, components, networks, systems, subsystems, or means, and/or (c) a functional relationship in which the operation of any one or more devices, apparatus, files, programs, media, components, networks, systems, subsystems, or means depends, in whole or in part, on the operation of any one or more others thereof. 
     In one advantageous embodiment, a universal control system for a tap-changer for retrofit or new tap-changer equipment is provided, the control system comprising, an electronic board rack for receiving various electronic boards, and a plurality of boards positioned in the electronic board rack, the plurality of boards selected to variously send and/or receive analog and/or digital signals to and from the existing tap-changer equipment. The system is provided such that the plurality of boards each has at least one channel, and the analog and digital input and output signals directly couple to the control system via a network connection by means of the plurality of boards. The system is further provided such that the analog and digital input and output signals are individually configurable on each channel on each board. 
     In another advantageous embodiment, a diagnostic system for protecting a tap-changer is provided comprising, a sensor positioned to detect temperature changes, and an initial measured temperature, indicating an initial temperature measured by the sensor prior to initiating a tap change. The system further comprises a calculated temperature value, calculated according to the particular tap change to take place, and a threshold value determined based on the initial measured temperature and the calculated temperature value, at which an alarm is generated. They system still further comprises a second measured temperature indicating an actual temperature measured by the sensor after a tap change has been initiated. The system is provided such that the alarm is generated by the diagnostic system if the second measured temperature exceeds the threshold value. 
     In still another advantageous embodiment, a diagnostic system for preventing degradation to electrical contacts in a tap-changer is provided comprising, a contact measurement device for measuring a contact position, and a contact signal generated by the contact measurement device, indicative of whether the contact is open or closed. The system further comprises a threshold time value related to a maximum amount of time that the contact may be closed, and a controller for receiving the contact signal and generating a closed time value based on the contact signal. The system is provided such that the controller compares the closed time value to the threshold time value to determine if the closed time value exceeds the threshold time value. The system still further comprises a warning message generated by the diagnostic system indicating that the threshold time value has been exceeded. 
     Other objects of the invention and its particular features and advantages will become more apparent from consideration of the following drawings and accompanying detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of one advantageous embodiment of the present invention. 
         FIG. 2  is a block diagram according to  FIG. 1 , illustrating another advantageous embodiment of the present invention. 
         FIG. 3  is a block diagram according to  FIG. 1 , illustrating still another advantageous embodiment of the present invention. 
         FIG. 4A  is a flow diagram of one advantageous embodiment of the present invention according to  FIG. 1 . 
         FIG. 4B  is a continuation of the flow diagram according to  FIG. 4A . 
         FIG. 5  is a flow diagram of one advantageous embodiment of the present invention according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views. 
       FIG. 1  illustrates one advantageous embodiment of universal control system  10  and generally comprises transformer (tap-changer and cooling group(s))  12 , transformer cabinet  14  and tap-changer control system  16 . 
     Transformer (tap-changer and cooling group(s))  12  is, in one advantageous embodiment, provided with temperature sensors  18 , which are provided to sense the temperature in the vicinity of the tap-changer and transformer top oil and transformer bottom oil temperatures. Temperature sensors  18  may comprise virtually any type of commercially-available temperature sensors. 
     Transformer (tap-changer and cooling group(s))  12  may also be variously provided with contact sensor  22  for measuring the total time a contact (not shown) has been closed, and with a current sensor  24  to measure the amount of current passing through the contact. 
     In one embodiment, the signals generated by the various sensors (i.e. temperature sensor  18 , contact sensor  22  and current sensor  24 ) may be transmitted via a coupling  26  to processor board  30  positioned on electronic board rack  28  located inside cabinet  14 . It is contemplated that the various sensors may communicate with universal control system  10  via, for example, a Control Area Network bus. 
     Processor board  30  is coupled to electronic board rack  28  by means of a bus  32 , onto which, processor board  30  may be attached. Also depicted in  FIG. 1  are peripheral board  1  ( 34 ) through peripheral board n ( 34 ′), which indicates that virtually any number of various peripheral boards ( 34 ,  34 ′) may be attached to bus  32  and are selected based on the particular application. Processor board  30  and peripheral boards ( 34 ,  34 ′) variously communicate with the transformer (tap-changer and cooling group(s))  12  via a coupling  36 . 
     It is contemplated that a relatively wide variety of peripheral boards ( 34 ,  34 ′) may be made available to communicate with existing tap-changers and/or existing cooling group(s). The signals may comprise, for example but are not limited to, sent and/or received analog and/or digital signals in a wide variety of signal formats. This versatility is advantageous because the wide variety peripheral boards ( 34 ,  34 ′) may be selected from to interface with existing equipment each having particular signal formatting and structure. 
     An interface converter  38  is further positioned in the station control room. Interface converter  38  is provided to send and receive the various analog and/or digital input and output signals from TCP/IP over a network connection  40 . 
     Network connection couples electronic board rack  28  to an OPC server. By way of example and not limitation, network connection in a preferred embodiment comprises a serial communication to Ethernet. However, it is further contemplated that network connection  40  could comprise any one or more of, for instance, the Internet, an intranet, a LAN (Local Area Network), a WAN (Wide Area Network) or a MAN (Metropolitan Area Network), a frame relay connection, an Advanced Intelligent Network (AIN) connection, a synchronous optical network (SONET) connection, a digital T 1 , T 3  or E 1  line, Digital Data Service (DDS) connection, DSL (Digital Subscriber Line) connection, an ATM (Asynchronous Transfer Mode) connection, FDDI (Fiber Distributed Data Interface) or CDDI (Copper Distributed Data Interface) connections. 
     Tap-changer control system  16  may further generate and alarm  42  when certain criteria are met. 
     Turning now to  FIG. 2 , processor board  30  is illustrated in greater detail. In this particular embodiment, temperature signal  44 , voltage signal  46 , contact signal  48  and current signal  50  are shown coupled  26  to processor board  30 . It should be noted that any of the various sensors illustrated in  FIG. 1  may be utilized either alone or in any combination. It should further be noted that, while all of the temperature signals are shown coupled  26  to processor board  30 , it is contemplated that any or all of the signals may instead be coupled to peripheral boards ( 34 ,  34 ′) as desired. 
     Illustrated on processor board  30  is first threshold temperature  52 , which is related to an initial temperature measurement, taken prior to a tap-change maneuver. The temperature is further measured after the tap-change maneuver for a selected time period, (i.e. five minutes) but may comprise any time period desired. The second temperature measurement is compared to the first threshold temperature and if the first threshold is exceeded  54 , a temperature alarm signal  56  may be generated. 
     Also illustrated in  FIG. 2  is threshold time value  58 , which may comprise a total time value that the contact (not shown) has been closed. The total time value may, in one advantageous embodiment, take into consideration the measured temperature at or near the tap-changer, the time the contact has been closed and the total amount of current passed through the contact. Each of these measurements can affect the total time value. If the threshold time value is exceeded  60 , a contact alarm signal  62  may be generated. 
     Still further illustrated in  FIG. 2  is second temperature threshold  64 , which is related to the initial temperature measurement taken prior to a tap-change maneuver and further includes compensation for the maneuver(s) to take place. If the temperature measurement taken after the tap-changer maneuver exceeds the second temperature threshold  66 , a power interruption signal  68  may be generated in order to interrupt power to the equipment to prevent damage and/or excessive wear thereto. 
     While these various calculations are illustrated as performed locally by processor board  30 , it is contemplated that they may be variously performed by peripheral cards ( 34 ,  34 ′) or by tap-changer control system  16  with the variously boards acting to transmit the data to and from transformer (tap-changer and cooling group(s))  12 . 
     Also illustrated in  FIG. 2  is cooling control signal  80 , which may include for example, the start/stop temperature for each cooler  82  for control of the various cooling groups. Finally, tap-changer control signal  84  is shown sent via bus  32  to any of the various boards  30 ,  34 ,  34 ′. 
     Referring now to  FIG. 3 , tap-changer control system  16  is illustrated in greater detail. 
     For example, alert signals  70  are shown sent via bus  32   a  to tap-changer control system  16  and include, for instance, temperature alarm signal  56 , contact alarm signal  62  and power interruption signal  68 . Once an alert signal  70  is received, tap-changer control system  16  may then take appropriate action including generation of a particular alarm or interrupting the electrical power to the tap-changer and cooling group(s)  12  and may include a notification of such a shutdown. Please note that while the alarm generation is illustrated as generated in tap-changer control system  16 , it is contemplated that it may be accomplished by processor board  30  or other equipment. 
     Data signals  72  are illustrated as sent to tap-changer control system  16  and may include the various measurement signals  44 ,  46 ,  48  &amp;  50  listed in connection with  FIG. 2 . Also illustrated is first temperature threshold  74  and second temperature threshold  76 , which may be either calculated by the system depending upon the initial temperature taken before the tap-change maneuver and the particular maneuver to take place. Alternatively, either or both of these thresholds may be set by user input criteria  78 . 
     In this manner, a versatile control system is provided that may effectively and efficiently be integrated with, for example, existing tap-changer equipment and cooling groups. Typically, the electronic board rack  28  may be retrofit into the tap-changer cabinet  14 , eliminating the need to re-wire or install new equipment. In fact, it is contemplated that existing sensor may further be utilized limiting the need to re-wire existing control wiring. 
     Turning now to  FIGS. 4A and 4B , a flow diagram of one advantageous embodiment of universal control system  10  is illustrated. When a signal has been received that a tap-change maneuver shall take place, an initial step of measuring the temperature in the tap-changer  102  is performed. Once this measurement is taken, the measurement may then, in one embodiment, be stored  104  as desired. 
     It is also contemplated that it may be desired to determine the particular tap-change maneuver to take place  106  so as to calculate a reference temperature  108  related to the particular tap-change maneuver. This reference temperature may then be stored  110 . 
     The system may then proceed to set a first threshold value for an alarm condition to occur based on the initial temperature measurement  112 . Still further, the system may then set a second threshold value for an interruption of electrical power based on the reference temperature value  114 . Alternatively, it is contemplated that both steps  112  and  114  may be accomplished by direct user input criteria from a user(s). 
     At this point the particular tap-change may be performed  116 . After the tap-change has been accomplished, it is contemplated that it is advantageous to measure the temperature in the vicinity of the tap-changer for a specified time period, such as for example, but not limited to, five minutes after the maneuver is performed. 
     The next step for the system is to determine if this selected time period has expired  118 . If the time period has expired, the system can proceed to finish  120  until another tap-change is to take place. If however the time period has not expired, the system proceeds to measure the temperature in the vicinity of the tap-changer  122 . 
     Once this measurement is obtained, the system may then determine if the measured temperature exceeds the first threshold value  124 . If this has not occurred, the system returns to querying whether the time period has expired  118 . If the temperature measurement does exceed the first threshold value, the system may generate and send a temperature alarm  126 . 
     After a temperature alarm is generated and sent  126  the system may then determine whether the measured temperature exceeds the second threshold value  128 . If not, the system returns to querying whether the time period has expired  118 . If however, the second threshold value is exceeded, the system may then proceed to send a trip signal. Optionally, the system may further generate and send a notification of the interruption  132 . The system may then finish  120  awaiting reset whether locally or remotely. 
     Referring now to  FIG. 5 , a flow diagram of another process performed by system  10  is illustrated. 
     Initially, the system determines a threshold value that is representative of the total time a contact may be closed  202 . The system may take into consideration temperature measured in the tap-changer and the current passing through the contact. 
     The system then performs a series of measurements including, for example, measuring the time the contact has been closed  204 , measuring the temperature in the tap-changer  206 , and measuring the current passing through the tap-changer  208 . 
     Once all of this information has been gathered, the system may then generate a closed time value based on the measured, time, temperature and current  210 . The various measure each affect the closed time value. For example, the higher the temperature measurement, the shorter the closed time value will be. Further, the lower the current, the longer the closed time value will be. In this manner, the system can compensate for many factors that can affect carbonization of the contact so as to substantially avoid any carbonization taking place. 
     The system then determines whether the closed time value exceeds the threshold value  212 . If not, the system proceeds to back to measuring the various values including time, temperature and current. If however, the system determines the closed time value does exceed the threshold value, the system may proceed to generate a warning message  214 . The warning message may contain a message that the contact needs to be exercised or changed to avoid carbonization. 
     It should be noted that, while various functions and methods have been described and presented in a sequence of steps, the sequence has been provided merely as an illustration of advantageous embodiments, and that it is not necessary to perform these functions in the specific order illustrated. It is further contemplated that any of these steps may be moved and/or combined relative to any of the other steps. In addition, it is still further contemplated that it may be advantageous, depending upon the application, to utilize all or any portion of the functions described herein. 
     Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.