CN112018733B - Regional differential protection method applied to feeder automation - Google Patents

Abstract

The invention discloses a regional differential protection method applied to feeder automation, and relates to the field of intelligent power grids and distribution automation. At present, the conventional feeder line has the problem of repeated power failure impact of users with non-fault paths. The invention comprises the following steps: communication synchronicity confirmation; confirming the communication validity, namely confirming the communication validity of the latest sampling point number after the unit confirms the communication synchronism; calculating analog quantity data; and performing area differential protection judgment according to the sigma I value. The technical scheme solves the defects of the conventional FA, does not cause power failure of the whole distribution line when the distribution line fails, and avoids repeated power failure impact on non-fault path users in the fault isolation and power restoration processes. The problem of distribution network protection cooperation under ring network structure and distributed generator access environment is solved. The application object is not limited to a single radiation type network any more, and can be applied to a power distribution primary network frame with any complex ring network structure, and the application range is wide.

Description

A regional differential protection method applied to feeder automation

technical field

The invention relates to the field of smart grid and distribution automation, in particular to a regional differential protection method applied to feeder automation.

Background technique

Feeder automation (feeder automation) is the basis of distribution automation (DA) and the core content of distribution automation. At present, the feeder automation projects that have been implemented in my country are generally aimed at single-radiation networks. Even if the primary distribution grid has a ring network structure, in actual operation, the tie switch is disconnected using an open-loop operation mode. Therefore, when implementing the construction of the feeder automation project, it is still designed according to the single-radiation network. On the one hand, realizing the power transfer function through feeder automation is one of the main purposes of feeder automation. The violation of the design and transformation purpose of the primary distribution grid ring network structure is a waste of investment in distribution automation construction.

With the introduction of distributed power generation (DG), the operation and management of traditional distribution networks has become more complex. In a certain sense, each distributed power source and the original single-radiation network have formed a miniature distribution ring network structure. The access of a large number of distributed power sources is a more complex distribution network with a multi-ring network structure in the form of a mesh compared to the conventional distribution ring network structure powered by two-sided power sources. Since the distribution ring network structure is unavoidable, DA and feeder automation must be designed and constructed for the ring network structure.

Protection and distribution automation under the environment of ring network structure and distributed power access need to consider the bidirectionality of power flow and fault current, as well as the difference in the magnitude of fault current in different directions and the difference in corresponding protection settings. Since the traditional protection configuration and conventional feeder automation (such as voltage-time feeder automation, voltage and current time feeder automation) can no longer meet the requirements, new ideas must be developed in the protection configuration and feeder automation project design.

Conventional feeder automation technology, whether it is centralized feeder automation, or local feeder automation technology such as voltage time feeder automation, voltage and current time feeder automation, and self-adaptive integrated feeder automation, has the following defects:

(1) When the fault occurs, the outgoing switch of the substation trips, causing the entire line to lose power. For on-site feeder automation, it is also necessary to set the reclosing function of one to three times on the outgoing circuit breaker of the substation. During the process of fault isolation and power supply recovery, the line will be impacted many times, and the users of the non-fault path will also experience repeated interruptions and restarts. Electricity.

(2) The conventional feeder automation is a technical solution developed for the single-radiation network. When it is applied to the primary distribution grid with a ring network structure, the tie switch must be disconnected and the open-loop operation mode is adopted, resulting in investment in the construction of distribution automation. waste

(3) For multi-connection lines, when the operation mode is changed, in order to ensure the correct action of the feeder automation, it is necessary to adjust the protection settings, especially for lines with multiple branches and there are sectionalizers on the branches. The adjustment of the protection settings is extremely complicated. Furthermore, for the distribution network in the environment where the distributed power supply is connected, the traditional protection will fail or become insensitive due to the injection of DG, or the adjustment of the protection setting will become impossible.

SUMMARY OF THE INVENTION

The technical problem to be solved and the technical task proposed by the present invention are to perfect and improve the existing technical solutions, and to provide a regional differential protection method applied to feeder automation, so as to reduce the multiple power failure and restoration shocks of non-fault path users the goal of. Therefore, the present invention adopts the following technical solutions.

A regional differential protection method applied to feeder automation, comprising the following steps:

1) Communication synchronization confirmation

After the node unit is reset and running, the communication synchronization is confirmed by sending the unit and feeding back the latest sampling point number of the receiving unit;

2) Confirmation of communication validity

After the communication synchronization of the unit is confirmed, confirm the communication validity of the latest sampling point number;

3) Analog data calculation

After the synchronization of data communication and confirmation of validity, when the latest sampling point number is equal to an integer multiple of the number of sampling points per cycle, calculate the analog data once, including the voltage and current, to obtain the ΣI of each area;

4) According to the value of ΣI, carry out regional differential protection judgment;

401) For the fault judgment and processing of the closed area, for any closed area, as long as ΣI>Id, it is judged that the fault is located in this area, and all switches corresponding to this area immediately start the protection trip;

402) Fault judgment and processing for non-enclosed areas; for any non-enclosed area, as long as one node in the area detects the fault current, it is judged that the fault is located in this area, and all switches corresponding to this area immediately start the protection trip;

403) Failure processing; when the voltage and current data synchronization fails, that is, when the data synchronization and validity cannot be guaranteed, the power distribution terminal automatically exits the regional differential protection mechanism, and the conventional protection is responsible for fault judgment and processing;

404) Failure processing; when the power distribution terminal fails to drive the switch to trip, that is, when the switch refuses to move, the power distribution terminal of this node should immediately notify all nodes in another area to which it belongs to trip the switch, and close the switch.

As a preferred technical means: in step 1) the communication synchronization confirmation includes the following steps:

101) Continue to broadcast the latest sampling point number of this unit for 5 cycles, and receive the "latest sampling point number" of each unit on the left and right sides;

102) When sending data for the second time, send the latest sampling point number of the unit and the latest sampling point number of the adjacent unit received last time;

103) Calculate the difference between the latest sampling point number sent back by the unit last time and the latest sampling point number just sent by the unit, and determine whether the difference is less than the number of 5/4-cycle sampling points.

104) When the difference is less than the number of 5/4 cycle sampling points, it is considered that the received data is synchronized, otherwise the unit receives a data synchronization alarm, and the differential protection of the unit area is blocked.

105) After confirming the data synchronization, take the sampling point number of the zero-crossing point of Uab from negative to positive for the first time as the latest sampling point number = 0.

As the preferred technical means: in step 2) the confirmation of the validity of the communication includes the following steps:

201) Continue to broadcast the latest sampling point number of this unit for 5 cycles, and receive the latest sampling point number of each unit on the left and right sides;

202) Calculate the difference between the latest sampling point numbers of each unit on the left and right sides received twice adjacently. The difference should be less than the number of sampling points of 1/4 cycle. At this time, the received data is considered valid, otherwise the received data for this unit is invalid. Alarm and block the differential protection of the unit area; in the normal operation of the device, the sampling point number validity self-check is also continuously maintained.

As the preferred technical means: before confirming the synchronization of communication and confirming the validity of the communication, it also includes the pre-sequence steps: waiting for the return of the tripping result, judgment of the failure to transmit the drive trip, judgment of the regional differential blocking state, and judgment of the closed area; regional differential protection Include the following steps:

a) judge whether to wait for the trip result to return; if so, go to step j), if not, go to step b);

b) judge whether it fails to transmit the drive trip, if so, enter step i), if not, then enter step c);

c) judge whether it is in the regional differential blocking state; if so, enter step 1), if not, then enter step d);

D) judge whether this area is a closed area; if otherwise enter step e), if yes, then enter step f);

e) determine whether there is a fault current; if so, enter step i), if not, enter step 1);

f) judge whether the data is synchronized and valid, if so, enter step g), if not, then enter step l);

g) Calculate ΣI;

h) judge whether ΣI>Id, if so, enter step i), if not, enter step l);

i) The drive switch trips and starts to wait for the operation result to return timing;

j) judge whether the action fails; if so, enter step k), if not, then enter step l);

k) Inter-area transfer of action failure information;

l) Switch the process of selecting another area, and then return to step a) until the end.

As the preferred technical means: the application subject of regional differential protection is the intelligent power distribution terminal used in conjunction with the power distribution switch), and the application object is an area of the power distribution network;

The distribution switch and the intelligent distribution terminal form a node; the intelligent distribution terminal realizes data collection and can communicate with other adjacent intelligent distribution terminals, and the intelligent distribution terminal can also control the trip/close of the switch; the control switch includes circuit breaker device or load switch;

Several nodes and the distribution lines surrounded by these nodes form a differential area, referred to as the area; when there is a boundary switch node in the area, the area is a non-enclosed area, otherwise it is a closed area;

Any one of the nodes must belong to two of the regions, and only belong to two regions; if the current flowing through one node is inflow for one region, it must be outflow for the other region, if the former is defined as positive, then the latter is negative;

When the switch of a node refuses to act, the current of another area to which the node belongs will be replaced by the switch with the same flow direction.

As a preferred technical means: it also includes a node definition step; the node includes information:

Static information: node type, node identification, node addressing information;

Real-time dynamic information: switch status, current data, voltage data.

As a preferred technical means: it also includes a region definition step; each region contains at least the following information:

Node linked list: node 1, node 2, node 3, node 4, ...;

Status flag information: communication synchronization flag, data valid flag, regional differential blocking flag, action failure region transfer flag, waiting for action result return flag, waiting for action result return timing;

ΣI calculated value.

As a preferred technical means: the power distribution terminal at least includes the following two tasks:

Communication maintenance and data collection tasks: maintain synchronous communication between regional nodes to ensure the validity of data; write real-time dynamic information data into the data structure of each node;

Regional differential protection task, realize the control of regional differential protection.

As the preferred technical means: switch configuration: circuit breakers are configured from substation outlet switches, line segment switches, and demarcation switches;

Protection fit:

Conventional protection configuration: All switches are equipped with three-stage protection, and the three-stage protection is fast break, overcurrent stage 1 and overcurrent stage 2; when the regional differential protection mechanism fails, the conventional protection works normally, and the conventional protection acts as a zone Backup protection for differential protection.

The outgoing switch node, segment switch node and end node of the substation are all circuit breakers. The three types of nodes have a three-level protection differential coordination through the setting of the start-up delay and the protection setting.

As the preferred technical means: terminal node delay = 0ms, all segment switch node delay = 150ms, substation outlet switch node delay = 250ms.

Beneficial effects:

1. Solve the defects of conventional FA. When the power distribution line fails, it will not cause a power outage of the entire line, and avoid multiple power outages and re-power shocks to non-faulty path users in the process of fault isolation and power supply recovery.

2. Solve the problem of distribution network protection coordination under the ring network structure and distributed power (DG) access environment.

3. The FA scheme based on this differential protection mechanism is no longer limited to single-radiation networks, but can be applied to primary distribution grids with any complex ring network structure, including active power distribution systems with distributed power (DG) access environments. distribution network.

The distribution automation terminal (FTU/DTU) and feeder automation (FA) technology have been raised to a new level, greatly improving the function and performance of feeder automation (FA), and expanding the application scope of FTU/DTU products and FA technical solutions . The promotion and application of FA based on regional differential protection has promoted the improvement of the level of distribution automation, thereby greatly improving the level of distribution network operation and management, and improving the reliability of power supply. Measured social benefits.

Description of drawings

Figure 1 is a diagram of a distribution circuit in a distributed energy access environment.

FIG. 2 is a diagram showing an example of the application of the regional differential protection of the present invention.

Figure 3 is a flow chart of the present invention.

Detailed ways

The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings.

As shown in Figure 3, the present invention comprises the following steps:

a) judge whether to wait for the trip result to return; if so, go to step j), if not, go to step b);

b) judge whether it fails to transmit the drive trip, if so, enter step i), if not, then enter step c);

c) judge whether it is in the regional differential blocking state; if so, enter step 1), if not, then enter step d);

D) judge whether this area is a closed area; if otherwise enter step e), if yes, then enter step f);

e) determine whether there is a fault current; if so, enter step i), if not, enter step 1);

f) judge whether the data is synchronized and valid, if so, enter step g), if not, then enter step l);

g) Calculate ΣI;

h) judge whether ΣI>Id, if so, enter step i), if not, enter step l);

i) The drive switch trips and starts to wait for the operation result to return timing;

j) judge whether the action fails; if so, enter step k), if not, then enter step l);

k) Inter-area transfer of action failure information;

l) Switch the process of selecting another area, and then return to step a) until the end.

The following is a detailed description of some of the contents:

1 Contents of the invention

The core content of the present invention has the following 4 items:

(1) For the distribution network, the concepts of "node" and "area" are abstracted, and the "node and area relationship theorem" and "node action transfer theorem" based on the concept of node and area are invented.

(2) Invented a voltage and current data synchronization technology that realizes peer-to-peer communication between switch nodes, which is the basis for the realization of "regional differential protection mechanism".

(3) Invented a regional differential protection mechanism that can be applied to distribution automation FA scheme. The distribution automation FA technical scheme constructed based on this mechanism can greatly improve the overall technical level of FA and distribution automation.

(4) Invented a program architecture system that can realize regional differential protection mechanism for distribution terminal FTU/DTU products. This architecture system can be used as a general design idea and method for the design and development of distribution terminal FTU/DTU products.

Figure 1 is a typical structural diagram of a distribution line in a distributed energy access environment. After the introduction of regional differential protection technology, the protection setting is for one area. According to Kirchhoff's current law, for an area ΣI=0, theoretically, the regional protection setting in any environment is 0. The actual protection setting value should be a certain value Id greater than 0. This Id has nothing to do with the region, and is only related to the sampling and calculation errors of each component in ΣI. That is to say, in the conventional FA technology, the problems of difficulty in adjusting the protection setting value and inability to set it do not exist at all in the regional differential protection technology.

The problem of setting the fixed value is solved, the outgoing switch of the substation in the fault processing process of the conventional FA technology is tripped, which causes the power failure of the entire line, and the impact on the line caused by multiple reclosing is also solved.

2 Concept Definitions and Related Theorems

The application subject of the regional differential protection mechanism is the intelligent distribution terminal (FTU) used in conjunction with the distribution switch, and the application object is an area of the distribution network. Before discussing the regional differential protection mechanism, first define the concept of area, and the concept of nodes related to the concept of area:

(1) Node: Power distribution switch + intelligent power distribution terminal (FTU) is a node. The FTU realizes data collection and can communicate with other adjacent FTUs. The FTU can also control the trip/close of the switch (circuit breaker or load switch). There are a total of 11 nodes in Figure 1, they are CB1, CB2, S1-S9.

(2) Differential area: Several nodes and the distribution lines surrounded by these nodes form a differential area, referred to as area. In the power distribution network shown in Figure 1, (CB1, S1, S2), (S2, S3), (S3, S4, S5) are three differential areas, and these three areas have 3, 2, and 3 switches respectively. These switch nodes are the boundaries between inside and outside the region. There is no other boundary except these switch nodes. They are all closed regions.

The node S1 belongs to the boundary switch node of the user branch line, which is commonly referred to as the end node. The property rights and management of the part after the node are assigned to the user and are not under the jurisdiction of the power distribution department. The node CB1 is the outgoing switch node of the substation, which belongs to the demarcation point of substation and power distribution. For both cases, we define another type of region: a non-enclosed region. The former is expressed as (S1, Null) or (Null, S1), and the latter is expressed as (CB1, Null) or (Null, CB1). The difference between the non-enclosed region and the closed region is that it has a Null boundary that is not a switch node.

For the power distribution network shown in Figure 1, the following 12 areas can be abstracted, of which 7 are closed areas and 5 are non-closed areas:

l Area (NULL, CB1), which is a non-enclosed area

l Area (CB1, S1, S2)

l Area (S1, NULL), which is a non-enclosed area

l Area (S2, S3)

l Area (S3, S4, S5)

l Area (S5, NULL), which is a non-enclosed area

l Area (S4, S6)

l Area (S6, S7)

l Area (S7, S8, S9)

l Area (S9, NULL), which is a non-enclosed area

l Area (S8, CB2)

l Area (CB2, NULL), which is a non-enclosed area

(3) Node and region relationship theorem: any node must belong to two regions, and only belong to two regions. The current flowing through a node, if it is inflow for one area, must be outflow for another area, if the former is defined as positive, the latter is negative.

(4) Node action transfer theorem: If the switch of a node refuses to act, the action should be replaced by a switch whose current flows in the same direction (inflow/outflow) in another region to which the node belongs.

3 Voltage, current and quantity data synchronization technology

The realization of the regional differential protection mechanism must be based on the peer-to-peer communication between nodes and the synchronization of voltage and current data between nodes. Therefore, the synchronization of communication between nodes must be solved, and the validity of data must be guaranteed.

1. Confirmation of communication synchronization

After the reset operation of the node unit, the communication synchronization should be confirmed by sending the unit and feeding back the "latest sampling point number" of the receiving unit. The process is as follows:

l Continuous 5-cycle broadcast to send the "latest sampling point number" of the unit and receive the "latest sampling point number" of each unit on the left and right sides;

l When sending data for the second time, send the "latest sampling point number" of the unit and the "latest sampling point number" of the adjacent unit received last time;

l Calculate the difference between the “latest sampling point number” sent by the unit last time and the “latest sampling point number” just sent by the unit, and the difference should be less than the number of 5/4-cycle sampling points.

l At this time, it is considered that the received data is synchronized, otherwise the unit receives a data synchronization alarm (self-check signal), and the differential protection of the unit area is blocked.

l After confirming the data synchronization, take the sampling point number of the zero-crossing point when Uab changes from negative to positive for the first time as "the latest sampling point number = 0".

2. Confirmation of communication validity

After the communication synchronization of the unit is confirmed, the communication validity should be confirmed through the "latest sampling point number" immediately. The process design is as follows:

(1) Continue to broadcast the "latest sampling point number" of the unit for 5 cycles and receive the "latest sampling point number" of each unit on the left and right sides;

(2) Calculate the difference between the "latest sampling point numbers" of each unit on the left and right sides received twice in a row. The difference should be less than the number of sampling points of 1/4 cycle. At this time, the received data is considered valid, otherwise the unit is received. Data invalid alarm (self-test signal), block differential protection of the unit area. During the normal operation of the device, the sampling point number validity self-check should also be continuously maintained.

3. Analog data calculation

After data communication synchronization and validity confirmation, in order to ensure continuous synchronization, when the latest sampling point number is equal to an integer multiple of the number of sampling points per cycle, calculate the analog data (voltage and current) once. The sampling point number cannot be readjusted due to the amount of mutation.

Since the synchronization of the data of each switch node in a region has been guaranteed, and these data are valid, then the ΣI of each region can be calculated.

4 Regional differential protection mechanism

The theoretical basis of the regional differential protection mechanism is Kirchhoff's current law. For any enclosed area, when the line is normal, the following constraints are satisfied:

ΣI < Id

For the non-enclosed region, the current value beyond the Null horizon cannot be obtained, and the above constraint cannot be used.

The control strategies corresponding to the regional differential protection mechanism are as follows:

(1) Fault judgment and treatment for closed areas. For any enclosed area, as long as ΣI>Id, it is judged that the fault is located in this area, and all switches corresponding to this area immediately start the protection trip.

(2) Fault judgment and processing for non-enclosed areas. For any non-enclosed area, as long as one node in the area detects the fault current, it is judged that the fault is located in this area, and all switches corresponding to this area immediately start the protection trip.

(3) Failure handling. When the voltage and current data synchronization fails (data synchronization and validity cannot be guaranteed), the FTU automatically exits the regional differential protection mechanism, and the conventional protection is responsible for fault judgment and processing.

(4) Failure handling. When the FTU-driven switch fails to trip (the switch refuses to actuate), the FTU of the node should immediately notify all nodes in another area to which it belongs to trip the switch, and close the switch.

Regarding the typical power distribution network in Figure 1, the differential protection mechanism is analyzed for the failure of F1-F5, as shown in Figure 2.

F1 fault: F1 is located in the non-enclosed area (S1, NULL), S1 detects the fault current, the quick-break protection acts, and S1 trips. If S1 refuses to act, CB1 and S2 act to trip.

F2 fault: ΣI (S2, S3)>Id, S2, S3 action trip. If S2 refuses to act, CB1 and S1 act to trip. If S3 refuses to act, then S4 and S5 act to trip.

F3 fault: F1 is located in the non-enclosed area (S5, NULL), S5 detects the fault current, the quick-break protection acts, and S5 trips. If S5 refuses to act, then S3 and S4 act to trip.

F4 fault: because the tie switch S6 is in the disconnected state, I(S6)=0, ΣI(S6, S7)>Id, S7 trips. If S7 refuses to act, then S8 and S9 act to trip.

F5 fault: ΣI (S7, S8, S9)>Id, the regional differential protection mechanism starts S7, S8, S9 action trip. If S7 refuses to act, since S6 is originally in the open state, S6 is closed and closed. If S8 refuses to act, then CB2 acts to trip.

5 Program architecture system of power distribution terminal products

1. Metadata structure

Define two types of data structures of nodes and regions, and treat these two types of data structures as metadata structures.

(1) Node description

To describe a node, at least the following information needs to be defined:

l Static information: node type, node identification, node addressing information

l Real-time dynamic information: switch status, current data, voltage data

(2) Area description

For any node, it must belong to and only belong to 2 areas, so it is necessary to define 2 areas: area 1 and area 2, each area contains at least the following information:

l Node linked list (node 1, node 2, node 3, node 4,...)

l Status flag information: communication synchronization flag, data valid flag, regional differential blocking flag, action failure region transfer flag, waiting for action result return flag, waiting for action result return timing

l Calculated value of ΣI

2. Program tasks

A distribution terminal consists of at least the following two tasks:

(1) Communication maintenance and data collection tasks

l Maintain synchronous communication between regional nodes to ensure the validity of data

l Write real-time dynamic information data into each node data structure

(2) Regional differential protection tasks

l Realize the control strategy of regional differential protection, as shown in Figure 3.

This basic application technology can be applied to FTU/DTU product development and distribution automation FA implementation.

1. FTU/DTU product development

The invention is the extension of the function of the FTU/DTU product, especially the improvement of the protection function of the FTU/DTU product.

When the present invention is implemented in the development of FTU/DTU products, in general, it can be based on the original hardware platform of the product, and does not need to change or increase the original hardware platform, but only needs to add nodes and areas on the original software platform. The definition of the class data structure, and adding a special task for regional differential.

2. Implementation of distribution automation FA

The distribution automation FA technical scheme with regional differential protection mechanism is based on the realization of peer-to-peer communication between FTU/DTU. If the DTU is used in power distribution rooms, switch stations and other places, the communication between nodes belongs to the station, and wired communication can be used, such as network communication based on local area network. If the FTU is applied to the line switch, the communication between the FTUs belongs to the long-distance inter-station communication, and the optical fiber communication method can be selected. In the future, the 5G communication method can also be selected.

In addition, FA based on regional differential protection also has certain requirements for switch and protection configuration when FA is implemented.

(1) Switch configuration

Based on the FA of regional differential protection, the protection function can drive the switch to trip when the line is faulty. Therefore, from the substation outlet switch, line segment switch, to the demarcation switch (end node), circuit breakers must be configured instead of load switches.

(2) Protection cooperation

Conventional protection configuration: All switches (circuit breakers) are configured with three-stage protection (quick break, overcurrent stage 1 and overcurrent stage 2). When the regional differential protection mechanism fails, the conventional protection works normally, so the conventional protection is the backup protection of the regional differential protection.

The outgoing switch node, segment switch node, and end node of the substation are all circuit breakers. The three types of nodes have a three-level protection level difference coordination through the setting of the start-up delay and the protection setting. For example, the end node delay=0ms, all segment switch nodes Delay = 150ms, substation outgoing switch node delay = 250ms.

A regional differential protection method applied to feeder automation shown in the above FIG. 3 is a specific embodiment of the present invention, which has embodied the substantial features and progress of the present invention, and can be used according to actual needs and under the inspiration of the present invention. , and equivalent modifications in terms of shape and structure are included in the protection scope of this scheme.

Claims (10)

1. A regional differential protection method applied to feeder automation is characterized by comprising the following steps:

1) communication synchronization confirmation

After the node unit is reset to operate, the latest sampling point number of the receiving unit is fed back by the node unit to carry out communication synchronism confirmation;

2) communication validity confirmation

After the unit communication synchronism is confirmed, the communication validity of the latest sampling point number is confirmed;

3) analog data calculation

After data communication synchronization and validity confirmation, when the latest sampling point number is equal to the integral multiple of the sampling point number of each cycle wave, calculating once analog quantity data including voltage quantity and current quantity to obtain sigma I of each area;

4) according to the sigma I value, judging the regional differential protection;

401) judging and processing faults of the closed regions, namely judging that the faults are located in the region as long as Σ I > Id for any closed region, and immediately starting protective tripping operation by all switches corresponding to the region;

402) judging and processing faults aiming at the non-closed area; aiming at any non-closed area, if only one node in the area detects fault current, the fault is judged to be in the area, and all switches corresponding to the area immediately start protection tripping;

403) performing failure treatment; when the voltage and current magnitude data synchronization fails, namely the data synchronism and effectiveness are not guaranteed, the power distribution terminal automatically exits from a regional differential protection mechanism and is subjected to conventional protection to be responsible for fault judgment and processing;

404) failure processing; when the power distribution terminal drive switch fails to trip, namely the switch refuses to operate, the power distribution terminal of the node immediately informs all the node switches of the other region to which the power distribution terminal belongs to trip, and closes the switch in a locking manner;

the distribution lines surrounded by the nodes form a differential area, which is called an area for short; when the boundary switch node exists in the region, the region is a non-closed region, otherwise, the region is a closed region.

2. The regional differential protection method applied to feeder automation as claimed in claim 1, wherein: the communication synchronicity confirmation in step 1) includes the steps of:

101) continuously broadcasting for 5 cycles to send the latest sampling point number of the unit and receive the latest sampling point number of each unit on the left and right sides;

102) when the data is sent for the second time, the latest sampling point number of the unit and the latest sampling point number of the adjacent unit received for the first time are sent out;

103) calculating the difference value between the latest sampling point number sent by the feedback unit for the first time and the latest sampling point number sent by the feedback unit for the second time, and judging whether the difference value is less than 5/4 cycle sampling points;

104) when the difference value is less than the 5/4 cycle sampling point number, the received data is considered to be synchronous, otherwise, the unit receives data synchronous alarm and locks the unit area differential protection;

105) after data synchronization is confirmed, the sampling point number of the Uab zero-crossing point changed from negative to positive for the first time is set as the latest sampling point number = 0.

3. The regional differential protection method applied to feeder automation as claimed in claim 2, wherein: the communication validity confirmation in step 2) includes the steps of:

201) continuously broadcasting for 5 cycles to send the latest sampling point number of the unit and receive the latest sampling point number of each unit on the left side and the right side;

202) calculating a difference value of the latest sampling point numbers of the units on the left side and the right side received twice adjacently, wherein the difference value is less than the 1/4 cycle sampling point number, the received data is considered to be valid at the moment, otherwise, the unit receives invalid data and alarms, and the differential protection of the unit area is locked; the sampling point number validity self-check is continuously kept during the normal operation of the device.

4. A regional differential protection method applied to feeder automation according to any one of claims 1 to 3, characterized in that: before the confirmation of communication synchronism and communication validity, the method also comprises the preamble steps: waiting for the trip result to return to judge, judging the failure transfer drive trip, judging the regional differential locking state and judging the closed region; the regional differential protection comprises the following steps:

a) judging whether a trip result is to be returned or not; if yes, entering step j), if not, entering step b);

b) judging whether the transmission of the drive trip fails or not, if so, entering a step i), and if not, entering a step c);

c) judging whether the locking device is in a regional differential locking state; if yes, entering step l), and if not, entering step d);

d) judging whether the area is a closed area; if not, entering the step e), and if so, entering the step f);

e) judging whether fault current exists; if yes, entering the step i), and if not, entering the step l);

f) judging whether the data are synchronous and effective, if so, entering a step g), and if not, entering a step l);

g) calculating the sigma I;

h) judging whether the Id is sigma I, if yes, entering the step I), and if not, entering the step l);

i) driving the switch to trip, and starting to wait for the operation result to return to time;

j) judging whether the action fails; if yes, entering step k), if not, entering step l);

k) transferring the action failure information between areas;

l) switching the process of selecting another area, then returning to step a) until the end.

5. The regional differential protection method applied to feeder automation as claimed in claim 4, wherein: the application main body of the regional differential protection is an intelligent power distribution terminal matched with a power distribution switch for use, and an application object is a region of a power distribution network;

the power distribution switch and the intelligent power distribution terminal form a node; the intelligent power distribution terminal realizes data acquisition and can communicate with other adjacent intelligent power distribution terminals, and the intelligent power distribution terminal can also control the tripping/closing of a switch; the control switch comprises a circuit breaker or a load switch;

a plurality of nodes and distribution lines surrounded by the nodes form a differential area, which is called an area for short; when a boundary switch node exists in the region, the region is a non-closed region, otherwise, the region is a closed region;

any node necessarily belongs to 2 areas, and only belongs to 2 areas; the current flowing through a node must be an outgoing current for one region if it is an incoming current for another region, and a negative current for the latter if the former is defined as positive;

when the switch of one node is refused to act, the current of another area to which the node belongs is the switch with the same flow direction to replace the action.

6. The regional differential protection method applied to feeder automation as claimed in claim 5, wherein: also includes the node definition step; the node includes information:

static information: node type, node identification and node addressing information;

real-time dynamic information: switch state, current magnitude data, voltage magnitude data.

7. The regional differential protection method applied to feeder automation as claimed in claim 6, wherein: also comprises a region definition step; each region contains at least the following information:

node chain table: a corresponding node number;

status flag information: communication synchronization mark, data effective mark, area differential locking mark, action failure area transmission mark, action result return waiting mark and action result return waiting timing;

calculating the value of Σ I.

8. The regional differential protection method applied to feeder automation as claimed in claim 1, wherein: the power distribution terminal at least comprises the following two tasks:

communication maintenance and data collection tasks: synchronous communication between the regional nodes is maintained, and the validity of data is ensured; writing real-time dynamic information data into each node data structure;

and the regional differential protection task realizes the control of regional differential protection.

9. The regional differential protection method applied to feeder automation as claimed in claim 8, wherein:

switch configuration: the circuit breakers are arranged from a substation outgoing switch, a line section switch to a boundary switch;

protection and matching:

conventional protection configuration: three-stage protection is configured for all switches, wherein the three-stage protection comprises a quick break section, an overcurrent 1 section and an overcurrent 2 section; under the condition that the regional differential protection mechanism fails, normal protection works normally, and the normal protection is used as backup protection of the regional differential protection;

the outgoing line switch node, the sectional switch node and the tail end node of the transformer substation are all circuit breakers, and the three types of nodes have 3-level protection level difference matching through setting of starting delay and protection fixed values.

10. The regional differential protection method for feeder automation according to claim 9, wherein: the delay of the tail end node is =0ms, the delay of all the section switch nodes is =150ms, and the delay of the substation outlet switch node is =250 ms.

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