Patent Description:
An electrical power transmission/distribution network, often referred to as an electrical grid, typically includes a number of power generation plants each including a number of power generator units, such as gas turbine engines, nuclear reactors, coal-fired generators, hydro-electric dams, etc. The grid may also include wind and/or solar energy generation farms. Not only are there many different types of energy generators on the grid, but there are also many different types of loads, and the generators and loads are distributed over large geographic areas. The transmission grid carries electricity from the power plants over long distances at high voltages. The distribution grid, separated from the transmission grid by voltage-reducing substations, provides electricity to the consumers/loads.

Many portions of the distribution grid, commonly known as feeders, are interconnected in a way where each feeder has a primary source (i.e., substation) which normally powers the feeder. Ends of the feeder opposite the primary source, where the feeder connects with adjacent feeders, are bounded by normally-open tie switches which isolate one feeder from the other. These tie switches can be closed to temporarily restore power to part of one feeder downstream of an isolated fault by providing the power from the adjacent feeder. Additional switches are also typically placed along the length of a feeder, thereby creating multiple feeder sections each separated by a switch, where each feeder section typically serves multiple customers.

Control of the feeder switches has been largely automated in recent years, using a strategy known as fault location, isolation and service restoration (FLISR). FLISR applications can reduce the number of customers impacted by a fault by automatically isolating the trouble area and restoring service to remaining customers by transferring them to adjacent circuits. In addition, the fault isolation feature of the technology can help crews locate the trouble spots more quickly, resulting in shorter outage durations for the customers impacted by the faulted section.

FLISR implementations can be separated into two main categories - centralized and distributed. In centralized control, data from the switch devices is transferred to a common central location where decisions are made. Centralizing FLISR decisions at a control center enables big-picture optimization of restoration tactics, but requires real-time communication of device status throughout the system. In distributed control, decisions about service restoration are made using logic and data available in the switch devices themselves, rather than at a common control center. Distributed FLISR control does not rely on the extensive real-time communication as in centralized FLISR control, but distributed FLISR has until now required either information from only adjacent devices, leading to less-than-optimal outcome, or information from all devices in the feeder and possibly adjacent feeders, reducing reliability when this information becomes unavailable.

<CIT> describes a power distribution protection system and method that uses communications to coordinate operation of fault protection devices. Communications may be prioritized wherein messages of a lower priority are held or discarded in favor of messages of a higher priority, for example, messages indicating a fault condition.

<CIT> describes a system for controlling a multifeed power distribution network. The network includes a first network sector that includes a first plurality of devices connected to a first power source and a second network sector that includes a second plurality of devices connected to a second power source. The system includes a first controller and a second controller. The first controller is configured to control operation of the first network sector and exchange data with the second controller. The second controller is configured to control operation of the second network sector and exchange data with the first controller.

<CIT> describes distributed feeder automation, in particular methods for decentralized configuration of feeder topology based on the adjacency relationship of switches.

In view of the above, there is a need for a distributed FLISR methodology which does not require switch devices to know the topology of adjacent feeders on the distribution grid in order to provide service restoration.

According to a first aspect of the invention, there is provided a method for providing fault location, isolation and service restoration for a group of interconnected feeders in a distribution grid according to claim <NUM>.

According to a second aspect of the invention, there is provided a system of interconnected distribution grid feeders providing fault location, isolation and service restoration according to claim <NUM>.

Optional and/or preferable features are laid out in the dependent claims.

Additional features of the present disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.

The following discussion of the embodiments of the disclosure directed to a technique for implementing distributed fault location, isolation and service restoration (FLISR) in a group of interconnected feeders without switch devices having knowledge of adjacent feeder topology is merely exemplary in nature, and is in no way intended to limit the disclosure or its applications or uses.

An electrical power grid consists of a transmission network and a distribution network. The transmission network handles the movement of electrical energy at high voltage over long distances from a generating site, such as a power plant, to an electrical substation. The distribution network moves electrical energy on local wiring between substations and customers. Because the distribution portion of the grid includes power lines which are susceptible to problems such as downed power poles and downed tree limbs, faults are relatively common on the distribution grid. Fault location, isolation and service restoration (FLISR) is the name given to a set of techniques used to recover from faults on the distribution grid.

The distribution grid is generally divided into units known as feeders. A feeder provides electrical energy to many end customers - including houses, businesses, factories, etc. Each feeder has a main energy source at one end and may have one or more boundaries with adjacent feeders at ends opposite the main source, where the adjacent feeders each have their own main source. The sources are typically substations, where high voltage energy (often several hundred thousand volts) on the transmission grid is transformed down to medium voltage energy (less than <NUM>,<NUM> volts). The main source is normally connected to and provides the power to the feeder, while the boundaries with the adjacent feeders are normally disconnected by an open tie switch. Along the length of each feeder, normally-closed switches are provided at intervals, where these normally-closed switches can be opened to isolate a fault in the feeder.

It is to be understood that the feeders described herein are three-phase networks. That is, each feeder includes three lines (L<NUM>, L<NUM>, L<NUM>), each <NUM>° out of phase with the others. The end customers may receive electrical service from one or more of the phases, where the houses almost always have single-phase service, and the businesses and factories may have three-phase service if they have high energy demands and/or large inductive loads such as motors. Each of the switches mentioned above is capable of opening or closing the feeder circuit for any individual phase as well as for all three phases.

If a fault occurs in a feeder, such as for example a lightning strike which damages or knocks down one or more power lines in a section between two normally-closed switches, it is possible to isolate the fault by opening the switches on each side of the fault and restore power to downstream sections by closing a tie switch to an adjacent feeder. This fault isolation and service restoration could be performed by line service crews visually locating the fault and manually opening and closing switches. A much better alternative is the use of FLISR techniques, which have resulted in fault isolation and service restoration happening automatically and very fast.

However, centralized FLISR techniques require real-time communication between the switches and a common controller, so that voltage and current measurements at each device, along with device open/closed status, can be used to command and control the status of other adjacent devices. These real-time communication-based FLISR techniques work well as long as the communication channels are operable but are completely defeated if the communication channels or the central controller are inoperable. Even with current technology, any communication medium can experience an outage - whether due to equipment failure, infrastructure damage, wireless signal interference or jamming, computer malware, or otherwise. A communication outage represents a single point of failure for centralized FLISR systems.

Distributed FLISR techniques do not require the extensive two-way communication of centralized FLISR. However, traditional distributed FLISR techniques require each switch device to have knowledge of the topology of not only their own feeder, but also adjacent feeders. This requirement for extensive system topology knowledge adds complexity to distributed FLISR implementations, is difficult to maintain accurately in the midst of fault events, and limits flexibility in responding to multiple faults. For these reasons, a new FLISR technique which relies only on the topology knowledge necessary for restoration is needed.

The present disclosure provides a technique for implementing distributed FLISR without switch devices being required to have knowledge of adjacent feeder topology. This scheme simplifies system configuration, and enables service restoration downstream of a faulted section quickly, even in the presence of other faults in adjacent feeders, while also preventing overload conditions. Preventing lengthy loss of voltage in sections downstream of a fault can avoid unwanted disconnection of important devices and can reduce the number of customers affected by the outage.

In the disclosed method, all switch devices initially determine information about their neighbor devices, including an X/Y orientation direction for each switch. This topology information is propagated to all switches within the feeder but need not be communicated to devices in adjacent feeders. Only the open tie switches which form the boundary between adjacent feeders need to have information about both feeders. When a fault occurs, conventional techniques are used to isolate the fault by opening one or more normally-closed switches. Then the switches which just opened use the topology knowledge of their feeder to find one or more open ties in a direction opposite the fault, and request restoration via closing of those ties. The actual restoration is not initiated by the ties until status of the adjacent feeder is checked and it is ascertained that overload conditions can be avoided. Thus, fault isolation and service restoration are accomplished solely based on knowledge local to each feeder and communication only within the feeder, with no need for communication to a common multi-feeder control center.

The following discussion of <FIG> provides a detailed explanation and examples of the techniques for distributed FLISR without system-wide topology knowledge described briefly above. Throughout this discussion, it should be understood that each of the switch devices includes voltage and current measurement sensors, a controller or processor which receives the measurements from the sensors and performs the calculations and logic of the disclosed methods, and an actuator capable of opening or closing the switch (for all three phases) upon command from the controller. Each of the switch devices also includes a communication module capable of communicating with other switches within its own feeder, including the tie switches at the ends. Communication between non-adjacent devices may be accomplished by relaying messages through devices located in between.

<FIG> is a schematic diagram <NUM> of a group of interconnected feeders in a normal fault-free condition, illustrating switch connectivity information known by each switch, according to an embodiment of the present disclosure. In the example illustrated in <FIG>, which is followed through subsequent steps in <FIG>, four adjacent feeders are shown, with interconnections as discussed above. Throughout the following discussion, the term upstream is used to mean in a direction closer to the source, while downstream means in a direction further from the source.

A feeder <NUM> is shown with an irregular shape outlined with a dashed line and a shaded background. The feeder <NUM> includes a source <NUM> at the left end, and normally-closed switches <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> along the length of the feeder <NUM>. At the far-right end of the feeder <NUM>, a tie switch <NUM> defines a boundary between the feeder <NUM> and an adjacent feeder <NUM>. Tie switches are normally-open devices, as discussed above. The feeder <NUM> also includes two branch points, each of which leads to a boundary with another feeder. A tie switch <NUM> defines a boundary between the feeder <NUM> and an adjacent feeder <NUM>, and a tie switch <NUM> defines a boundary between the feeder <NUM> and an adjacent feeder <NUM>.

The feeder <NUM> includes a source <NUM> and a normally-closed switch <NUM> and terminates at the tie switch <NUM> at the boundary with the feeder <NUM>. The feeder <NUM> includes a source <NUM> and normally-closed switches <NUM> and <NUM>. A tie switch <NUM> defines a boundary between the feeder <NUM> and the feeder <NUM>, and the tie switch <NUM> defines the boundary between the feeder <NUM> and the feeder <NUM>. The feeder <NUM> includes a source <NUM>, and normally-closed switches <NUM>, <NUM> and <NUM>. The tie switch <NUM> at the boundary with the feeder <NUM>, and the tie switch <NUM> at the boundary with the feeder <NUM>, were mentioned above.

In the disclosed restoration method, each of the switches is designated with a local X and Y direction. This X/Y directional designation is assigned to both normally-closed switches and to normally-open tie switches. The selection of the X and Y directions for each switch is arbitrary; it doesn't matter which direction is defined as X and which as Y, as long as the definition is adhered to consistently once designated. The X/Y directional designations for all of the switches are shown on <FIG> and subsequent figures.

A topology list for each feeder is created by propagating each switch's neighbor information throughout the entire feeder by switch-to-switch communication. For example, the switch <NUM> determines that it has the source <NUM> as its neighbor on the X side, and the switch <NUM> as its neighbor on the Y side. The switch <NUM> has the switch <NUM> as its neighbor on the Y side, and the switches <NUM> and <NUM> (on separate branches) as its neighbors on the X side. In this way, all of the switches in the feeder <NUM> have knowledge of their own connectivity, and this is shared to create a topology list for the feeder <NUM>, including the neighbors in each (X/Y) direction for each of the switches in the feeder <NUM>. Topology lists are similarly created for the devices in the feeders <NUM>, <NUM> and <NUM>.

The topology list is created and shared with all devices in each feeder at a time of normal operations, before a fault occurs, such as at the time when each feeder is created, or its topology is modified, or periodically to capture change in load. The fact that the topology list for each feeder only needs to be communicated to the devices in that feeder - not to the entire interconnected multi-feeder system - simplifies the operation of the disclosed method.

The tie switches which form a boundary between two adjacent feeders receive the topology list for both of the feeders which they connect. For example, the tie switch <NUM> receives the topology list for the feeder <NUM> and the feeder <NUM>, the tie switch <NUM> receives the topology list for the feeder <NUM> and the feeder <NUM>, etc..

Along with the topology list, an open tie "leader" must be designated for each feeder. The leader is the open tie which has the responsibility and the authority to make decisions for its feeder - in particular, authorizing closing a tie switch to connect the feeder to an adjacent feeder. The open tie leaders are designated with a * symbol, within the feeder for which the tie is the leader, on <FIG>.

The leader for each feeder may be selected based on a set of predetermined rules. A non-limiting list of examples for leader selection rules includes: selection based on switch RTU number (remote terminal unit; similar to an IP address); selection based on switch location within the feeder (where a central location may be preferable); and selection based on computing capacity or load-carrying capacity. Because the rules are pre-defined and the topology of each feeder is known for the normal operating conditions of <FIG>, the leader is therefore also known by applying the pre-defined rules to the normal topology.

For the normal operating conditions of <FIG>, the switch <NUM> is the leader for the feeder <NUM>, as indicated by the * located above-left of the switch <NUM>, within the outline of the feeder <NUM>. The switch <NUM> is also the leader (the only open tie) for the feeder <NUM>, as indicated by the * below-left of the switch <NUM>. Similarly, the switch <NUM> is defined as the leader for the feeder <NUM>, and the switch <NUM> is defined as the leader for the feeder <NUM>.

Using the topology lists and tie leader designations as defined above and the logic of the disclosed methods, service restoration can be accomplished following a fault, as illustrated in <FIG> and explained in the discussion below.

<FIG> is a schematic diagram <NUM> of the interconnected feeders <NUM>-<NUM> in a condition where a fault has just occurred, according to an embodiment of the present disclosure. A fault <NUM> is shown as occurring near the branch point between the switches <NUM>, <NUM> and <NUM> in the feeder <NUM>. The fault <NUM> may be any type of line-to-line, line-to-ground or open-circuit fault, such as a tree limb falling against one line (one phase) and either breaking that line or causing one line (phase) to contact another line, or causing a ground fault in the line.

When the fault <NUM> occurs, all areas of the feeder <NUM> will experience some kind of disturbance, as indicated by the dashed lines connecting the switches within the feeder <NUM>. The portions of the feeder <NUM> which are upstream of the fault <NUM> (that is, nearer to the source <NUM>) - which in this case are the switches <NUM> and <NUM> - will experience a high current on at least the one phase associated with the fault <NUM>. The portions of the feeder <NUM> which are downstream of the fault <NUM> - which are the sections of the feeder <NUM> to the right of the switch <NUM> and above the switch <NUM> - will likely experience a voltage drop or a complete loss of voltage on at least the one phase associated with the fault <NUM>.

<FIG> represents the instant at which the fault <NUM> occurs. No changes in configuration or status of the switches have yet happened in <FIG>. In <FIG> which follow, any switch which has changed status from the previous figure (from open to closed, or vice versa) is shown in bold line font, in order to make it easy to see what has changed. The graphical depictions of the switches are shown appropriately in all cases, whether open or closed.

<FIG> is a schematic diagram <NUM> of the interconnected feeders <NUM>-<NUM> in a condition where a normally-closed switch has opened in response to the fault <NUM>. When the fault <NUM> occurs, the switches <NUM> and <NUM> will detect an abnormally high current on at least one phase. Existing over-current protection schemes will cause the switch <NUM> to open to interrupt the fault and stop the abnormally high current. One example of such an existing protection scheme is where each switch is configured with time-current protection characteristics, where devices further from the source are configured to trip to an open position faster than devices which are nearer to the source. Using time-current protection characteristics in this manner and recognizing that the switches <NUM>-<NUM> do not experience excess current because they are not located between the source <NUM> and the fault <NUM>, the switch <NUM> will open fastest to stop the over-current situation and isolate the fault <NUM> from the source <NUM>. A switch may try to reclose into the fault several times. This allows full restoration in case of temporary or intermittent faults. After a predetermined number of reclose attempts, if the fault persists, the switch will lock out. Once a switch locks out, it will only close back upon a human-initiated command, either remotely (through SCADA for example) or locally by pulling a lever.

When the switch <NUM> opens as shown on <FIG>, this action isolates the fault <NUM> from the portions of the feeder <NUM> upstream of the switch <NUM>. Thus, as indicated by the solid line, service is now restored to customers located between the source <NUM> and the switch <NUM>, and customers located between the switch <NUM> and the switch <NUM>. Also, when the switch <NUM> opens, this action completely cuts power on all three phases to the portions of the feeder <NUM> downstream of the switch <NUM>. Thus, a complete loss of voltage is experienced in the fault area between the switches <NUM>, <NUM> and <NUM>, and to the right of the switch <NUM>, and also above the switch <NUM>.

<FIG> is a schematic diagram <NUM> of the interconnected feeders <NUM>-<NUM> in a condition where two other normally-closed switches have opened in response to a total loss of voltage. In <FIG>, the switches <NUM> and <NUM> have opened, and the switch <NUM> remains open as discussed above. This action isolates the fault <NUM> between the switches <NUM>, <NUM> and <NUM>. One way that the switches <NUM> and <NUM> may be configured to open and isolate the fault <NUM> is by passing isolating messages between the devices. In other words, when the switch <NUM> opens due to its time-current protection characteristics to isolate the fault <NUM> from the source <NUM>, the switch <NUM> can send a message to its downstream neighbor(s), which it knows from its topology list, telling the downstream neighbors that they must also open in order to fully isolate the fault <NUM> from the source <NUM>. Other control logic may also be used to cause the switches <NUM> and <NUM> to open upon detection of a complete voltage loss on all three phases.

With the isolating switches <NUM>, <NUM> and <NUM> open, the fault <NUM> is now isolated between these switches, and power is completely cut off to all portions of the feeder <NUM> downstream of the isolating switches. In order to restore power to the portions of the feeder <NUM> to the right of the switch <NUM> and above the switch <NUM>, open tie switches must be identified and closed to connect these sections to adjacent feeders. As discussed below, the present disclosure describes a method for restoration which does not rely on centralized communication and command, and does not require full network topology knowledge by all devices.

At some point in time after the isolating switches <NUM>, <NUM> and <NUM> open as shown in <FIG> and <FIG>, this change of status must be communicated to all of the switch devices in the feeder <NUM>, including to the tie switches <NUM>, <NUM> and <NUM>. In one embodiment of the disclosed method, the process of communicating the new state takes place after the whole event is over, and the ties are closed. At the point in time after the device opening shown in <FIG>, only the leaders need to know of the isolating switches, and they only need to know about the isolating switch which is still connected to them.

<FIG> is a schematic diagram <NUM> of the interconnected feeders <NUM>-<NUM>, illustrating how the three switches which opened to isolate the fault then identify open ties and request service restoration, according to an embodiment of the present disclosure. In this step, each of the isolating switches <NUM>, <NUM> and <NUM> uses its topology list to identify any open ties in the feeder <NUM> which are located in a direction opposite the fault <NUM>. To perform this step, the switches only need topology information about the feeder which they are part of. Here, the isolating switches make use of the X/Y directional information and the tie leader designations discussed earlier.

The switch <NUM> knows that the fault <NUM> is located on its X side, as shown in <FIG>. The switch <NUM> therefore looks in its topology list to find an open tie on its Y side. However, the switch <NUM> does not have an open tie on its Y side, as the source <NUM> is located in that direction. Thus, the switch <NUM> determines that there is no open tie other than itself to which a restoration request may be made, as indicated by arrow <NUM> which loops from the switch <NUM> back to itself. The arrow <NUM> looping back to the switch <NUM> itself does not mean that the switch <NUM> will re-close as part of the restoration process. As discussed above, the switch <NUM> is locked out in order to isolate the fault <NUM> from the source <NUM>, and to protect line workers when the fault <NUM> is being cleared. The switch <NUM> will therefore remain open until the fault <NUM> is cleared and the locked-out isolating switches (<NUM>, <NUM>, <NUM>) are re-closed manually by line workers or remotely by human-initiated command.

The switch <NUM> knows that the fault <NUM> is located on its X side, and therefore looks in its topology list to find any open ties on its Y side. The switch <NUM> finds that there are two open ties located in its Y direction - those being the switch <NUM> which forms a boundary with the feeder <NUM>, and the switch <NUM> which forms a boundary with the feeder <NUM>. The switch <NUM> is only allowed to send a restoration request to one open tie, so it must determine the leader for the feeder <NUM>. As discussed earlier, the switch <NUM> has been identified as the open tie leader for the feeder <NUM>, based on application of the pre-defined rules. The switch <NUM> therefore sends its restoration request to the open tie switch <NUM>, as indicated by arrow <NUM>. The switch <NUM> does not send a restoration request to the switch <NUM>.

It is important to understand that only a restoration request is being sent to the open tie <NUM>. Actual tie switch closing is not initiated yet, as further arbitration and authorization must occur before actual restoration of power, which will be discussed below.

The situation of the switch <NUM> can be handled in one of several ways, according to embodiments of the disclosed method. The switch <NUM> knows that the fault <NUM> is located on its Y side, as shown on <FIG>, and therefore looks in its topology list to find an open tie on its X side. The switch <NUM> finds that there is one open tie located in its X direction - that being the tie switch <NUM> which forms a boundary with the feeder <NUM>. However, the switch <NUM> was not originally the leader of the feeder <NUM>. In one approach of the method, the switch <NUM>, which knows the new topology of the feeder <NUM>, designates the switch <NUM> as the new leader of the section downstream of the switch <NUM> (designated by new * on Y side of switch <NUM>), and sends a restoration request to the tie switch <NUM> as indicated by arrow <NUM>. A second approach is for the switch <NUM> to send the request to the previously established leader, the switch <NUM>. The switch <NUM> will then designate the switch <NUM> as the new leader of the section downstream of the switch <NUM>, based on topology and switch opening information known to the leader switch <NUM>, and forward the restoration request to the switch <NUM>. A third approach is also for the switch <NUM> to send the request to the switch <NUM>, but then for the switch <NUM> to determine the restoration outcome for the section downstream of the switch <NUM>, and ask the switch <NUM> to close without designating it as a leader first. In any case, only a restoration request is sent to the switch <NUM>; actual tie switch closing is not initiated yet.

As mentioned above, the switch <NUM> identified two open ties to which it could potentially send a restoration request, selected a leader and sent the request to the tie switch <NUM>. Closing of either of the two open ties (<NUM> and <NUM>) downstream of the switch <NUM> must be coordinated with the other, in order to prevent an undesirable closed circuit between the two sources <NUM> and <NUM>. It should be noted that the method discussed above is otherwise inherently preventive of restoration requests which would connect two sources, as the isolating switches (<NUM>, <NUM> and <NUM>) which send the requests are open (locked out) and on different branches of the feeder <NUM>, thereby isolating any newly connected adjacent feeders from each other.

Thus far in the process, restoration requests have been sent to open tie switches, but no tie switches have yet been closed. In order to actually restore power to sections of the feeder <NUM> downstream of the switches <NUM> and <NUM>, tie switch closing must occur, thereby connecting the affected portions of the feeder <NUM> to an adjacent feeder and its power source.

Each open tie switch which receives a restoration request must first determine the best way to satisfy the request, and then receive permission from the leader of the adjacent feeder before closing the tie to that adjacent feeder. Recall that the switch <NUM> received a restoration request from the switch <NUM>. This restoration request could be satisfied by closing the tie switch <NUM> to the feeder <NUM>, or by closing the tie switch <NUM> to the feeder <NUM>. The request could even be satisfied by opening the switch <NUM> and then closing both the tie switches <NUM> and <NUM>. The best approach may be determined by the leader of the feeder experiencing the fault.

The switch <NUM> is the leader of the feeder <NUM>. Because the switch <NUM> is a leader, it has complete device status knowledge for its own feeder. For example, the leader switch <NUM> knows that the switch <NUM> opened in order to isolate a fault, that there is currently no power in the feeder <NUM> downstream of the switch <NUM>, and that a restoration request has been sent by the switch <NUM>.

The leader switch <NUM> also has limited knowledge of conditions on adjacent feeders, sufficient to enable restoration decision-making. For example, during the information propagation stage (discussed previously with respect to <FIG>), the switch <NUM> will share across the devices in the feeder <NUM> just the additional (excess) capacity available from the feeder <NUM>. The switch <NUM>, upon receiving the restoration request, will not have a full picture (topology and device status) of the feeder <NUM> since it is not part of that feeder. However, it will know how much capacity is available from the feeder <NUM>, how much capacity is available from the feeder <NUM>, and how much load needs to be picked up downstream of the switch <NUM>. This information is enough for the switch <NUM> to determine to best way to restore. If the switch <NUM> determines the best course of action is to close the switch <NUM>, it will ask the switch <NUM> to close.

Once the tie switch <NUM> is selected by the leader switch <NUM> to satisfy the restoration request from the switch <NUM>, the switch <NUM> must still receive authorization from the feeder <NUM> leader before actually closing. The switch <NUM> is the feeder <NUM> leader, and therefore can provide this authorization itself. Authorization for tie switch closing is only provided when the leader determines that the action will not create an overload situation for the feeder, and that current conditions in the feeder are suitable for tie-in of the adjacent feeder. For example, authorization of the tie switch closing would not be provided if the feeder <NUM> was currently experiencing a disturbance (fault) of its own, or if the source <NUM> was compromised in some way.

To summarize the above actions: the tie switch <NUM> (leader of feeder <NUM>) received a restoration request from the switch <NUM>; the tie switch <NUM> determined the best way to satisfy the request, using information known to it about topology (open ties which could potentially be closed) and excess capacity on adjacent feeders; the restoration action was assigned by the switch <NUM> to the tie switch <NUM>; and the tie switch <NUM> requested and received authorization to close from the feeder <NUM> leader. Using this approach, the tie switch leader (switch <NUM>) made the restoration decision using pre-defined rules and logic, and information already known to the leader about topology and adjacent feeder capacity. System-wide knowledge of status and topology by all switches is not needed, and system-wide communication to a central controller is not needed.

The tie switch <NUM> also received a restoration request in <FIG>. There is no alternative in this case, so the tie switch <NUM> does not need to determine if it is the best candidate. The tie switch <NUM> does, however, still need to request authorization from the feeder <NUM> leader, to determine if an overload condition will be created by its closing, and to ensure that conditions in the feeder <NUM> are suitable. In this case, closing of the tie switch <NUM> will only add a small load (customers located between the switch <NUM> and the switch <NUM>) to the feeder <NUM>, which is not likely to create an overload condition. The open tie switch <NUM> therefore requests and receives authorization to close from the feeder <NUM> leader, which is itself.

<FIG> is a schematic diagram <NUM> of the interconnected feeders <NUM>-<NUM> in a condition where two normally-open ties have closed in response to the restoration requests, according to an embodiment of the present disclosure. Based on the actions described above in connection with <FIG>, the open tie switch <NUM> closed to connect the switches <NUM> and <NUM> and their loads to the feeder <NUM>, and the open tie switch <NUM> closed to connect the switch <NUM> and its loads to the feeder <NUM>. This new configuration is shown in <FIG>, where the restored power is indicated by the solid circuit line in the portions of the feeder <NUM> to the right of the switch <NUM> and above the switch <NUM>.

When the tie switches <NUM> and <NUM> close as shown in <FIG>, this change of status is communicated to all of the switch devices in the affected feeders. Therefore, the feeder <NUM> now essentially includes all customers on both sides of the switches <NUM> and <NUM>, in addition to its own original customers, all powered by the source <NUM>. Using this revised topology list, the same logic described above for <FIG> could be employed again in the event of a subsequent fault. For example, if a subsequent fault occurred between the switches <NUM> and <NUM>, those two switches could be opened to isolate the fault, and the tie switch <NUM> could be closed for restoration of power to the switches <NUM> and <NUM> by connection to the feeder <NUM>.

It is worth mentioning again that all of this FLISR behavior is accomplished based on pre-defined network topology, local current and voltage measurements, pre-programmed behavioral logic at each switch, and communication to leader switches of state changes. No real-time communication from switches to a common controller is required as in centralized FLISR, and system-wide knowledge of all topology is not required as in previous distributed FLISR techniques. Furthermore, the disclosed next-generation distributed FLISR approach is adaptive to changing topology as switches open and close, and therefore able to continue isolation and restoration in the event of multiple faults as discussed above.

The fault isolation and service restoration scenario described above and shown in <FIG> is one of the more complex scenarios which may be imagined involving the feeders <NUM>-<NUM>, as the feeder <NUM> has boundaries with three adjacent feeders, and the fault location was at a branch point which involved three neighboring switches for isolation. From the above discussion of this complex scenario, the application of the disclosed techniques to simpler scenarios - with fewer open ties and fewer switch openings required for isolation - can be easily understood.

There are several significant benefits of the disclosed restoration method. One such benefit is better reliability. Under the centralized FLISR scheme, if the central controller stops working or communication channels are inoperable, system restoration stops. Under previous distributed FLISR schemes, if a source switch stops working, rapid self-healing is disabled. Under the new distributed scheme of the present disclosure, all open tie devices would have to stop working to prevent restoration, which would prevent service restoration under any scheme.

Another benefit of the disclosed next-generation distributed FLISR approach is lower communication requirements. Under the centralized FLISR scheme, all of the switch devices need to communicate with the central controller. This can add substantial latency due to the number of hops and/or communication channel congestion problems. Under the new distributed scheme of the present disclosure, only data for the feeder the device is part of needs to be propagated. The feeder topology is not rigid, and it is updated when it changes.

Yet another benefit of the disclosed next-generation distributed FLISR approach is better scalability. Under the centralized FLISR scheme, the central location needs to maintain and compute the entire network. Under the previous distributed scheme, rapid self-healing cannot handle multiple contingencies because the devices' roles are pre-defined. Under the new distributed scheme of the present disclosure, each device only needs to know about its neighboring devices, and roles evolve dynamically based on the system conditions.

<FIG> is a flowchart diagram <NUM> of a method for fault isolation and service restoration in a group of interconnected feeders, according to embodiments of the present disclosure discussed above in relation to <FIG>. At box <NUM>, each switch device determines its neighbor or neighbors in both the X and Y directions. This determination can be made via switch-to-switch communication, or by manual definition when each feeder is installed or modified. Information about each switch's X and Y neighbors is propagated via switch-to-switch communication throughout the entire feeder, so that all devices in each feeder - including the open ties at the boundaries with adjacent feeders - have a complete topology list for the feeder(s) to which they belong. Limited information - such as available excess capacity - from adjacent feeders is also propagated via switch-to-switch communication throughout each feeder at the box <NUM>.

At box <NUM>, an open tie leader is determined for each feeder in the group of interconnected feeders. The leader is determined based on the pre-defined rules for leader selection, which may include consideration of the location of each open tie within the feeder, the RTU number of the open ties, the computing or load-carrying capacity of each open tie, and/or other factors. At the box <NUM>, the open tie leader device is selected by applying those rules to the nominal conditions and configuration of each feeder.

At box <NUM>, when a fault occurs (<FIG>), a switch immediately upstream of the fault (nearer the source) opens and locks out due to its over-current protection characteristics. This was shown in <FIG>, where the switch <NUM> opened to isolate the fault <NUM> from the source <NUM>, thereby restoring power to the sections of the feeder <NUM> upstream of the switch <NUM>. At box <NUM>, the switch or switches immediately downstream of the fault open and lock out due to their detection of a loss of voltage on all three phases. This action was shown in <FIG>. The switches in the feeder may also pass messages - such as the switch <NUM> sending a message indicating it has locked out (opened) due to an over-current situation, whereupon the switches <NUM> and <NUM> know from the topology list that they are the neighbors of the switch <NUM> and that they must therefore lock out (open) in order to isolate the fault <NUM>.

At box <NUM>, each isolating switch identifies open ties in the direction opposite of the fault, from information in the topology list, and sends a restoration requests to one of those open ties. This action was shown in <FIG>. In many cases, there will be two isolating switches - one upstream and one downstream of the fault. However, in the case of the fault <NUM>, which is located at a branch point, there are three isolating switches. The switch <NUM>, upstream of the fault, does not have an open tie in a direction opposite the fault, and has already had service restored upstream of itself directly from the source <NUM>, and therefore the switch <NUM> identifies itself as the open tie and sends a message to itself. Even though it sends a restoration request to itself, the switch <NUM> will not re-close because it is locked out for fault isolation.

The switch <NUM> determines there are two open ties in its Y direction and therefore must identify the open tie leader device among those two open ties. The isolating switch <NUM> identifies the open tie switch <NUM> as the leader for the feeder <NUM>, and then sends a restoration request to the switch <NUM>. The switch <NUM> determines there is only one open tie in its X direction, that being the tie switch <NUM>, and therefore sends a restoration request to the switch <NUM>.

At decision diamond <NUM>, each open tie which receives a restoration request determines, from the topology list for the fault-affected feeder, whether any other alternative open ties exist for the portion of the affected feeder needing restoration. The switch <NUM>, which received a restoration request, determines that the switch <NUM> is an alternative for restoration of the affected portions of the feeder <NUM>. Therefore, at box <NUM>, the switch <NUM> decides between the alternative open ties (<NUM> and <NUM>) to determine the best option. As discussed earlier, the decision may include consideration of which adjacent feeder has the most excess capacity, consideration of the current status of each potential adjacent feeder (do any of them currently have faults and open isolating switches?), and other factors. In the case of <FIG>, the decision by the leader switch <NUM> identifies the open tie switch <NUM> as the best alternative, and therefore the restoration (closing) request is sent to the switch <NUM>.

At the decision diamond <NUM>, the open tie <NUM>, which received a restoration request from the switch <NUM>, determines that no alternative exists, and skips over the decision step at the box <NUM>.

At box <NUM>, open tie switches (which are selected for restoration) request permission for closing from the leader of the adjacent feeder to which they belong. Permission from the leader of the adjacent feeder is a different step than decision between alternatives. This permission request happens either after deciding between alternative open ties at the box <NUM>, or after determining that no alternatives exist at the decision diamond <NUM>. In <FIG>, as discussed above, the switch <NUM> identified the open tie switch <NUM> as the best alternative, and there was no alternative for the open tie switch <NUM>. Therefore, the open tie switch <NUM> must request permission to close from the leader of the feeder <NUM>, which is itself. Likewise, the open tie switch <NUM> must request permission to close from the leader of the feeder <NUM>, which is itself.

Before the open tie switches <NUM> and <NUM> are authorized to close at the box <NUM>, their leaders must first confirm that the condition of the adjacent feeder is suitable for taking on extra load from the feeder <NUM>. That is, the open tie leaders <NUM> and <NUM> confirm at the box <NUM> that the feeders <NUM> and <NUM> are in good condition (no faults in the process of being isolated) and there are no problems with the sources <NUM> and <NUM> which would prevent them from taking on the extra load from the feeder <NUM>. If adjacent feeder conditions are suitable, then permission to close is granted at the box <NUM>.

At box <NUM>, the open tie switches which have been selected and confirmed for restoration actually close. When these tie switches close, power is restored to downstream portions of the affected feeder. This action was shown in <FIG>, where the tie switch <NUM> closed to restore power to the right of the switch <NUM> in the feeder <NUM>, and the tie switch <NUM> closed to restore power above the switch <NUM> in the feeder <NUM>.

The process described in the flowchart diagram <NUM> isolates the fault <NUM> and restores service to portions of the feeder <NUM> downstream of the fault using only local information and measurements, and communication only within each individual feeder.

After the box <NUM>, the fault <NUM> is isolated and power has been restored to all downstream sections of the feeder <NUM>. The process then returns to the box <NUM> - to redefine the topology of the switches and the leader devices after recovering from a fault (to prepare for a possible subsequent fault, which could also be recovered from with only local in-feeder topology knowledge). This redefinition of the topology is easily accomplished in the manner discussed previously. For example, in <FIG>, the switch <NUM> is now closed, and the feeder <NUM> now includes the switches <NUM> and <NUM>. Meanwhile, the feeder <NUM> is unaffected by changes resulting from the fault <NUM> in the feeder <NUM>.

As will be well understood by those skilled in the art, the several and various steps and processes discussed herein to describe the disclosed methods may be referring to operations performed by a computer, a processor or other electronic calculating device that manipulates and/or transforms data using electrical phenomenon. In particular, this refers to the control calculations and operations performed by controllers or processors included in each of the switches in the feeders of <FIG>. Those processors and electronic devices may employ various volatile and/or non-volatile memories including non-transitory computer-readable medium with an executable program stored thereon including various code or executable instructions able to be performed by the computer or processor, where the memory and/or computer-readable medium may include all forms and types of memory and other computer-readable media.

Claim 1:
A method for providing fault location, isolation and service restoration for a group of interconnected feeders (<NUM>, <NUM>, <NUM>, <NUM>) in a distribution grid, the method comprising:
providing, to all switches (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in each individual feeder (<NUM>, <NUM>, <NUM>, <NUM>) in the group of interconnected feeders, a feeder topology list defining connectivity of the switches (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in the individual feeder (<NUM>, <NUM>, <NUM>, <NUM>), wherein each switch (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprises a processor configured to receive and maintain the feeder topology list once provided;
determining an open tie switch leader (<NUM>, <NUM>, <NUM>) for each of the individual feeders (<NUM>, <NUM>, <NUM>, <NUM>) for normal operating conditions, wherein the processor of each switch (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is further configured to receive and maintain open tie switch leader designation information;
opening one or more normally-closed switches (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in a fault-affected feeder (<NUM>, <NUM>, <NUM>, <NUM>) when a fault (<NUM>) occurs in order to isolate the fault (<NUM>);
sending a restoration request, by the one or more normally-closed switches (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) which opened, to an open tie switch (<NUM>, <NUM>, <NUM>, <NUM>) in the fault-affected feeder (<NUM>, <NUM>, <NUM>, <NUM>) which is located in a direction opposite the fault (<NUM>) and which forms a boundary with an adjacent feeder (<NUM>, <NUM>, <NUM>, <NUM>);
requesting permission to close from the open tie switch leader (<NUM>, <NUM>, <NUM>) of the adjacent feeder (<NUM>, <NUM>, <NUM>, <NUM>) by each of the open tie switches (<NUM>, <NUM>, <NUM>, <NUM>) which receives a restoration request; and
closing each of the open tie switches, when permission is received from the open tie switch leader, to restore power to a downstream section of the fault-affected feeder (<NUM>, <NUM>, <NUM>, <NUM>).