Abstract:
One embodiment provides a computer system for preventing switching errors in a power system that includes a plurality of switching devices. The system includes a topology-extraction mechanism configured to extract topology information associated with the power system; a status database configured to store status information associated with the switching devices; a rule database configured to store user-definable operation rules associated with the switching devices; a receiving mechanism configured to receive a request for performing a switching operation on a device; a simulation mechanism configured to perform a simulation based on the extracted topology information, the status information, and a rule associated with the device; a determination mechanism configured to determine whether the switching operation is allowed based on an outcome of the simulation; and a display mechanism configured to display an output of the determination mechanism.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/509,965, entitled “Method and System for Preventing Misoperation in an Electric Power System,” by inventors Shuqiang Jin, Lingzhi Pang, Liguo Wan, Jiandong Huang, and Hongping Jiang, filed 20 Jul. 2011. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates generally to management of an electric power system. More specifically, the present disclosure relates to a system used for preventing switching errors in an electric power system. 
     2. Related Art 
     In complex electric power plants or transmission substations, where various types of equipment are operating at high voltages, switching errors can lead to disastrous outcomes, such as interruptions of power, damages to equipment, and loss of human life. A number of factors can cause switching errors, including equipment failure, faults of the control system, human error, and inadequate interlocking devices. Statistics have shown that most switching errors are caused by human error, which can be prevented with proper interlocking design. 
     Common switching errors include energizing a grounded line, closing a ground switch when energized, de-energizing or load dropping using a disconnector instead of a breaker, or entering an energized switching bay. In order to prevent these switching errors, it is essential to ensure that the correct switching sequence is followed by the switching personnel. In addition, the switching personnel must be fully aware of the impact of each switching step and have the assurance that the next step is proven safe before the actual switching takes place. This requires a simulation system that models the connectivity of a substation and the interlocking logic among the switching operations. Before operating on a piece of equipment, a worker is required to perform a switching-sequence simulation, which verifies whether the sequence of operations complies with safety rules and regulations. If an operation step violates a safety rule, the simulation system notifies the worker such operation cannot proceed. 
     Conventional switching-sequence simulation systems rely on human programmers to generate and input logic expressions that describe operation of the equipment, which can require a huge amount of work for a large-scale, complex power system, and thus is prone to unintended omissions or typographical errors. In addition, operation of certain complex equipment (such as a bridge transformer) may involve complex logic, making it difficult to summarize all possible operating modes. 
     SUMMARY 
     One embodiment of the present invention provides a computer system for preventing switching errors in a power system that includes a plurality of switching devices. The system includes a topology-extraction mechanism configured to extract topology information associated with the power system; a status database configured to store status information associated with the switching devices; a rule database configured to store user-definable operation rules associated with the switching devices; a receiving mechanism configured to receive, from a user, a request for performing a switching operation on a device in the power system; a simulation mechanism configured to perform a simulation based on the extracted topology information, the status information, and one or more rules associated with the device; a determination mechanism configured to determine whether the switching operation is allowed based on an outcome of the simulation; and a display mechanism configured to display an output of the determination mechanism. The display mechanism is further configured to display an error message to the user in response to the switching operation not being allowed. 
     In a variation on this embodiment, the system further includes a transmission mechanism and a handheld smart key. The transmission mechanism is configured to transmit a switching order based on the outcome of the simulation to the smart key, and the smart key is configured to: identify the device in the field; and in response to the switching operation being allowed, unlock a lock associated with the device to allow the switching operation to be performed. 
     In a further variation, the smart key identifies the device by checking an RFID associated with the device. 
     In a variation on this embodiment, the switching devices include at least one electrically operated device and one manually operated device. 
     In a variation on this embodiment, the status database is configured to receive status information from a supervisory control and data acquisition (SCADA) system and/or a handheld smart key. 
     In a variation on this embodiment, the topology-extraction mechanism is further configured to construct a node table from a one-line diagram associated with the power system. 
     In a variation on this embodiment, the simulation mechanism is configured to perform the simulation by performing a search that traverses the power system topology based on the rule. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
         FIG. 1  presents a diagram illustrating the process of the “five-step” method, in accordance with an embodiment of the present invention. 
         FIG. 2  presents a diagram illustrating the architecture of a simulation-and-control system, in accordance with an embodiment of the present invention. 
         FIG. 3  presents a diagram illustrating the architecture of the simulation module, in accordance with an embodiment of the present invention. 
         FIG. 4  presents a flow chart illustrating the operation process of the switching-error prevention system, in accordance with an embodiment of the present invention. 
         FIG. 5  presents a portion of an exemplary one-line diagram. 
         FIG. 6  presents a diagram illustrating an exemplary user interface, in accordance with an embodiment of the present invention. 
         FIG. 7  presents a diagram illustrating an exemplary computer system for performing switching-order simulations, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
     Overview 
     Embodiments of the present invention provide a switching-sequence simulation system. The switching-sequence simulation system includes a simulation engine, a topology analyzer, and a rule database. The topology analyzer analyzes the topology of a substation based on the single-line diagram of the substation and constructs a node table, which includes status information of each node and the connectivity information among all nodes. The rule database stores a set of predetermined operation rules. Users of the simulation system are allowed to view and edit the operation rules stored in the rule database. In response to an operation request, the simulation engine calculates a switching logic expression based on the topology node table and the rule database. If the switching logic expression states that the requested operation is allowable, the switching-sequence simulation system notifies the user that the operation request is granted. Otherwise, the switching-sequence simulation system notifies the user that the operation request is denied. 
     Smart-Interlock System 
     To prevent possible switching errors involved in a switching operation, in embodiments of the present invention, a transmission substation or a switching/dispatching center implements a smart-interlock system (SIS), which combines the reliability of mechanical interlocking and the flexibility of electrical interlocking. The SIS includes a central simulation-and-control system, a smart key, and various types of locks; and uses a “five-step” method to ensure switching safety. The five steps for performing safe switching include: a simulation step, a switching-order transmission step, a device ID verification step, an operation-permission revalidation step, and a switching-completion step.  FIG. 1  presents a diagram illustrating the process of the “five-step” method, in accordance with an embodiment of the present invention. 
     Before an actual switching takes place, a simulation is performed to ensure that the proposed switching sequence is safe (operation  108 ). Note that this simulation can be performed by a simulation-and-control system  102  located in the substation control room. The switching-sequence simulation outputs a switching order that specifies which equipment is to be operated on and the order of the operations. Subsequently, the switching order is transmitted to a smart key  104  during the switching-order transmission step (operation  110 ). Smart key  104  is a handheld device that is capable of communicating, using various wireless communication protocols (such as ZigBee or CDMA), with the simulation-and-control system. In addition, smart key  104  is capable of interacting and unlocking various locks, such as a lock  106 , associated with the switching equipment. Note that the locks are attached to the equipment, and operations on the equipment require unlocking these locks using smart key  104 . Smart key  104  can be carried by a person designated to perform the switching operation in the field, where the equipment is located. During the device-ID verification step, the field person uses smart key  104  to verify that the equipment to be operated on is the identified equipment by checking an identifier associated with the equipment (operation  112 ). For example, a lock (such as a padlock) attached to the equipment can be embedded with an RFID, and an RFID detector included in the smart key can read this RFID in order to verify the identity of the equipment. Once the ID of the equipment to be operated on has been verified, the field person can optionally revalidate the operation by sending the operation request for the current equipment back to simulation-and-control system  102  via smart key  104  (operation  114 ) and receiving a validation result from simulation-and-control system  102  (operation  116 ). Note that this revalidation process (operations  114  and  116 ) is optional. Subsequent to receiving the revalidation result, the field person uses smart key  104  to unlock lock  106  (either an electronic lock or a mechanical lock) and performs the actual switching (operation  118 ). For example, the field person may need to unlock a padlock in order to move the swing handle of a disconnect switch; or he may need to unlock a lock on the door of a cabinet in order to operate on equipment inside the cabinet. Note that the operation can be a manual operation that requires the field person to physically move a switch handle or an automated, electrically operated operation. After completion of the switching operation, smart key  104  updates the status of the equipment by transmitting its current status back to simulation-and-control system  102  (operation  120 ). 
     Simulation-and-Control System 
     The simulation-and-control system is an essential part of the SIS. It uses the one-line diagram of a substation to obtain the circuitry topology; collects current equipment status; collects and models switching interlock logic and rules; and simulates the switching sequence based on the circuitry topology, current equipment status, and switching interlock logic and rules.  FIG. 2  presents a diagram illustrating the architecture of a simulation-and-control system, in accordance with an embodiment of the present invention. Simulation-and-control system  200  includes a simulation module  202 , a state machine  204 , a user interface  206 , and a control module  208 . 
     During operation, state machine  204  receives the current status of the equipment in a substation from a supervisory control and data acquisition (SCADA) system, which performs the remote operation surveillance for the SIS, and sends the equipment status information to simulation module  202 . Simulation module  202  performs switching sequence simulation using current equipment status, topology information extracted from the substation one-line diagram, and the switching interlock logic and rules. The detailed structure of simulation module  202  is shown in  FIG. 3 . Based on the simulation result, simulation module  202  generates a switching order. User interface  206  displays possible error information and system warnings, and communicates with the smart key. In addition, control module  208  issues control commands to the SCADA system to realize the remote control operations. 
     Simulation-and-control system  200  can reside on any type of computer system based on microprocessors, such as a standalone mainframe computer or a cluster of computer servers. 
       FIG. 3  presents a diagram illustrating the architecture of the simulation module, in accordance with an embodiment of the present invention. Simulation module  300  includes an equipment analyzer  302 , a status database  304 , a topology analyzer  306 , a rule database  308 , and a simulation engine  310 . 
     Equipment analyzer  302  analyzes the structural components of each piece of equipment associated with the switching operation, and decomposes a piece of complex equipment into a number of basic components, such as circuit breakers, disconnects, and ground disconnects, that fulfill the electrical functionality of the complex equipment. For example, a three-position knife switch is decomposed to two basic components: a knife switch and a ground knife switch. The three switching positions correspond to different switching positions of the knife switch and the ground knife switch. Note that after a piece of complex equipment is decomposed into multiple basic components, connections to other external equipment are mapped onto corresponding ends on the basic components. The output of equipment analyzer  302 , including the status of the basic components and their connection information, is stored in status database  304 . Note that the status information of the components can be updated by the smart key. In one embodiment, after each operation, the smart key updates the status of the equipment being operated on. Such an arrangement makes it possible for the system to maintain real-time status information of all equipment, including manually operated equipment in the field, such as a manual switch or a locked door for a switching bay. 
     Topology analyzer  306  analyzes the topology of a substation based on the one-line diagram and the decomposition outcome of each piece of complex equipment. In one embodiment, topology analyzer  306  constructs a node table, which includes the status of the nodes and connection information among the nodes. Note that each node in the node table corresponds to a topology node extracted from the one-line diagram of the substation. In one embodiment, a topology node corresponds to a crossing point on the one-line diagram, which can include one or more equipment endpoints. Note that a single topology node may be associated with multiple endpoints, whereas a particular endpoint can only be associated with a single topology node. 
     Rule database  308  stores switching interlock logic and rules, which can be either programmed ahead of time by the manufacturer of the SIS or defined by the user of the SIS. For example, to prevent operations on a loaded knife switch, rule database  308  stores a rule stating that no operation (either opening or closing) is allowed on a knife switch when the knife switch is coupled to a closed circuit breaker. Note that these rules generally describe allowed or disallowed operations of basic components, regardless of their relative locations in the system topology. The independent relationship between rule database  308  and the system topology provides scalability for the SIS. When the substation scales up, such as with the addition of new equipment, instead of reprogramming the entire simulation software, one only needs to input the updated one-line diagram into topology analyzer  306 . Moreover, when safety rules and regulations are changed, only rule database  308  needs to be updated. Such updating can be made by users of the SIS. In one embodiment, the switching interlock logic and rules are stored in a table, and the user is allowed to add, delete, or make changes to the table entries. In a further embodiment, an entry in rule database  308  includes three components: equipment type, operation type, and expression of the rule specific to the equipment and the operation. The equipment type component specifies the type of equipment (such as breakers, knife switches, and ground wires) that this rule is applied to; the operation type specifies which operation (such as opening or closing) that this rule is applied to; and expression of the rule is a logic expression describing the error-prevention rule. Such a logic expression is specific to the type of equipment and the type of operation, and remains unrelated to any specific piece of equipment within the system. In the aforementioned example, a corresponding entry for closing a knife switch in rule database  308  can be expressed as: KNIFE SWITCH, CLOSING: KNIFE SWITCH UNLOADED. Such a rule is applied to all knife switches in the system, including a knife switch that was included in and decomposed from a piece of complex equipment. 
     Once the system receives an operation request on a piece of equipment, simulation engine  310  performs a simulation to determine whether the requested operation is allowed based on the topology node table constructed by topology analyzer  306 , equipment status information extracted from status database  304 , and operation rules extracted from rule database  308 . 
       FIG. 4  presents a flow chart illustrating the operation process of the switching-error prevention system, in accordance with an embodiment of the present invention. Prior to receiving a request to perform a switching operation, the system goes through an initialization process, which includes receiving the one-line diagram of a power plant or a substation (operation  402 ), extracting topology information from the one-line diagram (operation  404 ), and constructing a topology node table (operation  406 ). Note that this initialization process can be performed when the power system is brought online, or when the power system experiences equipment update. The system waits for a request for an operation on a particular piece of equipment, such as a request for closing a knife switch (operation  408 ). Upon receiving such a request, the system extracts a rule associated with the equipment and the operation from the rule database (operation  410 ). Based on the rule, the system derives a number of operating conditions complying with the rule (operation  412 ). For example, a rule associated with closing a knife switch states that such an operation requires that the knife switch be unloaded, and the operating conditions that satisfy this rule include: all circuit breakers coupled to the knife switch being open, and at least one side of the knife switch being unloaded. 
     Based on the derived operating conditions, the system extracts a predefined search associated with that rule. Such a search starts from one or more endpoints of the equipment and traverses the electrical connectivity topology (operation  414 ). The targets and boundary of the search are defined by the operating conditions. For example, to determine whether the condition of all coupled circuit breakers being open is met, the system first defines a search boundary, which includes circuit breakers and open knife switches. In other words, a search originating from a node and traversing the topology will come to a stop once a circuit breaker or a knife switch is met. The search target is a closed circuit breaker. Note that if the search returns a closed circuit breaker, it indicate a violation of the operation condition. Similarly, to determine whether the condition of at least one end of the knife switch being unloaded is met, the system first defines a search boundary, which includes open circuit breakers and open knife switch. The search targets include loaded devices or a power supplies. The system then obtains the current status of the equipment within the topology (operation  416 ). In one embodiment, the system interfaces with an EMS (Energy Management System)/SCADA system to obtain the current operational status (such as positions of a switch) of the equipment. In a further embodiment, the current status of the equipment can be obtained by the smart key. 
     Subsequently, the system performs the search that traverses the topology (operation  418 ). The search starts from one or more endpoints of the equipment. In the example of the knife switch, the search starts from both ends of the knife switch. The search traverses the electrical connectivity topology, and collects equipment associated with the operating conditions. For example, using the operating condition that all circuit breakers coupled to the knife switch are open, the system defines a search boundary that includes open circuit breakers and open knife switches, and the search targets include loaded devices and power supplies. Based on the search result and the current equipment status, the system determines whether the operating conditions are met (operation  420 ). If the operating conditions are met, the system indicates to the user that the operation is allowed (operation  422 ). Otherwise, the system displays error information to the user (operation  424 ). In one embodiment, the error information includes the search result indicating the violated operating condition. In the example of the knife switch, the search may find a coupled circuit breaker having a current status of being closed, and indicate to the user that operations on the knife switch are prohibited due to the status of that particular circuit breaker. Note that such information can be used by the user to correct the situation. In the above example, the error information indicates that operations on the knife switch are prohibited because a coupled circuit breaker is closed. The user can then attempt to open the circuit breaker first in order to operate on the knife switch. In a further embodiment, if the violated operating condition is not a critical condition (such as a one that does not violate a safety rule), the error message may include an option that allows the user to override the decision made by the system. Based on the user&#39;s input, the system may indicate that such an operation is allowed or not. 
     An Operation Example 
       FIG. 5  presents a portion of an exemplary one-line diagram. One-line diagram  500  includes a breaker  502 , two knife switches  504  and  506 , and two ground switches  508  and  510 . During initialization, the switching-error prevention system extracts connectivity topology information from one-line diagram  500  and constructs a node table. The node table includes a number of topology nodes (such as nodes  512  and  514 ) and connectivity information associated with the switching devices. For example, one endpoint of ground switch  510  is coupled to an endpoint of knife switch  506  and an endpoint of breaker  502  at node  514 . 
     Upon receiving an operation request to close ground switch  510 , the system extracts a rule stating that before the closing operation can take place on a ground switch, the ground switch needs to be isolated from other equipment. Based on the rule, the system determines that the corresponding operating condition is that all knife switches coupled to ground switch  510  remain open. Based on the operating condition, the system defines a search for a closed knife switch coupled to ground switch  510 . This search starts from the ungrounded end of ground switch  510 , and traverses the entire topology The search boundary includes knife switches and the search targets include closed knife switches. An empty search result indicates that ground switch  510  is isolated from other equipment. Consequently, the system determines that the operating condition is met, and the operation of closing ground switch  510  is allowed. Note that if a knife switch coupled to ground switch  510 , such as knife switch  506 , is closed, the system will determine that the requested closing operation of ground switch  510  is prohibited, and display an error message to the user. The message can notify the user that the requested operation is prohibited because knife switch  506  is closed. 
     User Interface 
       FIG. 6  presents a diagram illustrating an exemplary user interface, in accordance with an embodiment of the present invention. In one embodiment, the switching-error prevention system includes a graphic user interface (GUI) that enables a user to interact with the switching-error prevention system. 
     The GUI can be presented to the user on various types of display mechanisms, such as a standard computer display or a touch-screen display. In  FIG. 6 , GUI  600  displays the one-line diagram of a substation. In one embodiment, the displayed one-line diagram also displays the current status of the equipment, such as a switch being open or close. A user can request an operation on a piece of switching equipment by pointing and clicking an icon on the diagram corresponding to the equipment. The simulation result in response to the operation request is presented to the user via GUI  600 . 
     In one embodiment of the present invention, GUI  600  can switch the view from the one-line diagram shown in  FIG. 6  to a view that displays a table associated with the rule database. The table view of the rule database enables the user to make changes to the rule database by adding, deleting, and modifying entries in the table. 
     Computer System 
       FIG. 7  presents a diagram illustrating an exemplary computer system for performing switching-order simulations, in accordance with an embodiment of the present invention. In one embodiment, a computer and communication system  700  includes a processor  702 , a memory  704 , and a storage device  706 . Storage device  706  stores a switching-order simulation application  708 , as well as other applications, such as applications  710  and  712 . During operation, switching-order simulation application  708  is loaded from storage device  706  into memory  704  and then executed by processor  702 . While executing the program, processor  702  performs the aforementioned functions. Computer and communication system  700  is coupled to an optional display  714 , keyboard  716 , and pointing device  718 . The display, keyboard, and pointing device can facilitate switching-order simulation. 
     The foregoing descriptions of embodiments of the present invention have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit this disclosure. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. The scope of the present invention is defined by the appended claims.