A method and system for protecting low-voltage busbars in distribution networks based on directional blocking

Abstract

This invention discloses a method and system for low-voltage busbar protection in distribution networks based on directional blocking. The method includes: S1. Real-time acquisition of current signals on the busbar and each branch circuit; S2. Calculation of current surges on the branch circuits, and determination of whether the current signal is abnormal based on the magnitude of the current surges; S3. When the current signal is determined to be in an abnormal state, the fault direction of the current is determined based on a current direction function; S4. The fault location is determined based on the fault direction of the current, and blocking logic is constructed based on the fault location. Determining the fault direction of the current based on a separate current direction function effectively overcomes the problem of overcurrent protection being prone to false tripping or failure to trip due to distributed power source access, and solves the problem of protection failure when the busbar voltage collapses. The method also has high speed of operation, meeting the rapid isolation requirements of active distribution networks to prevent cascading disconnection.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection, and in particular to a method and system for protecting low-voltage busbars in distribution networks based on directional blocking. Background Technology

[0002] With the large-scale integration of distributed power sources such as photovoltaics into the distribution network, the fault characteristics of low-voltage buses have changed. In active distribution networks, low-voltage buses serve as crucial hubs connecting upstream transformers, various distributed power sources, and user loads, making the reliability and speed of their protection schemes paramount. However, existing technologies for protecting low-voltage buses have the following drawbacks:

[0003] 1. Failure of Traditional Overcurrent Protection: The integration of distributed generation disrupts the unidirectional power flow pattern of the power grid. When a short-circuit fault occurs in the system, it provides boosting current to the fault point, making the magnitude and direction of the fault current no longer fixed. This directly causes traditional overcurrent protection, which relies on fixed thresholds and unidirectional flow, to lose its selectivity and sensitivity. It is highly susceptible to false tripping during faults outside the protection zone, or to failing to trip because the fault current is supported by distributed generation and falls below the set value, seriously threatening power supply safety.

[0004] 2. Low Reliability of Directional Protection Elements: Directional protection, introduced to address power flow direction issues, typically relies heavily on the bus voltage at the time of a fault as a reference for its directional judgment. However, in the event of severe faults such as metallic short circuits on low-voltage buses, the bus voltage can drop significantly, even approaching zero, leading to severe distortion or loss of the voltage signal. In such cases, voltage-dependent directional elements lose their reliable basis for judgment, resulting in a significant decrease in directional accuracy or even complete failure, severely limiting their application.

[0005] 3. Insufficient protection speed: Traditional bus protection schemes (such as time-delay-based regional interlocking protection) typically rely on current amplitude exceeding a set threshold and persisting for a period of time to determine a fault. This means that even if a fault occurs, it is necessary to wait for the current to reach a certain magnitude and persist for a sufficiently long time before triggering the protection action, which is difficult to meet the stringent requirements of modern active power grids. In power grids with a high proportion of distributed generation, once a fault occurs, isolation must be completed in an extremely short time to prevent large-scale cascading disconnection of distributed generation due to prolonged voltage drops, thereby threatening the stability of the entire system. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for protecting low-voltage busbars in distribution networks based on directional blocking, which solves the problem of failure of traditional overcurrent protection and improves the speed of protection.

[0007] This invention also provides a method for protecting low-voltage busbars in distribution networks based on directional blocking, the method comprising:

[0008] Real-time acquisition of current on the busbar and each branch circuit;

[0009] Calculate the current surge on the branch circuit, and determine whether the current signal is abnormal based on the magnitude of the current surge;

[0010] When the current signal is determined to be in an abnormal state, the fault direction of the current is determined based on the current direction function;

[0011] The fault location is determined based on the fault direction of the current, and a blocking logic is constructed based on the fault location.

[0012] Furthermore, calculating the current surge on the branch circuit includes:

[0013] The current surge on each branch circuit is calculated using a half-cycle differential algorithm.

[0014] The current surge is:

[0015] ;

[0016] in, Indicates the sudden change in current on the branch circuit described in the k-th clause; i k (t) represents the instantaneous current value on the branch circuit described in Article k at time t; T is a complete cycle of the alternating current.

[0017] Furthermore, determining whether the current signal is abnormal based on the magnitude of the current abrupt change includes:

[0018] If the current surge is greater than or equal to the first set threshold, the current signal is determined to be in an abnormal state.

[0019] Wherein, the first set threshold is a multiple of the rated current.

[0020] Furthermore, the current direction function is:

[0021] ;

[0022] Among them, i k (n) represents the nth discrete current sample value on the kth branch circuit, i ref (n) represents the nth discrete current sample value of the reference current; N represents the total number of data sample points used in a fault direction determination. This is the result of determining the direction of the current fault.

[0023] Furthermore, determining the fault direction of the current based on the current direction function includes:

[0024] like If the value is 1, then the fault is located on the bus side and the current is in a positive fault state.

[0025] like =-1, then the fault is located on the load side of the branch circuit and the current is in a reverse fault state;

[0026] The positive fault state refers to the fault state that occurs when current flows into the busbar; the reverse fault state refers to the fault state that occurs when current flows out of the busbar.

[0027] Furthermore, determining the fault location based on the fault direction of the current, and constructing the blocking logic based on the fault location includes:

[0028] If the current fault direction of any of the branch circuits is positive, then the fault point is determined to be located in that branch circuit, and the bus protection is activated.

[0029] If the current fault direction of all the branch circuits is reversed, then the bus protection is blocked, and the protection of the branch circuits is performed.

[0030] Furthermore, the method also includes setting a three-level timing determination mechanism;

[0031] The first-level timing determination mechanism involves detecting the sudden change in current within 0-2 milliseconds.

[0032] The second-level timing determination mechanism is a criterion for confirming the direction of the current within 2-5 milliseconds;

[0033] The third-level timing determination mechanism completes the criterion fusion and trip signal output within 5-10 milliseconds.

[0034] Furthermore, the criterion fusion includes:

[0035] The criteria for the tripping condition are generated by combining the amplitude of the current surge, the criterion for the direction of the fault current, and the duration of the current surge.

[0036] Furthermore, by combining the amplitude of the current surge, the criterion for determining the direction of the fault current, and the duration of the current surge, the criteria for generating the tripping condition include:

[0037] When the duration of the current surge exceeds the time threshold, the current of one of the branch circuits is in a positive fault state, and the amplitude of the current surge exceeds the current threshold, a tripping operation is performed on the bus.

[0038] When the amplitude of the current change in multiple branch circuits exceeds the time threshold and the current is in a positive fault state, an emergency trip operation is performed on the bus.

[0039] On the other hand, the present invention also provides a low-voltage busbar protection system for distribution networks based on directional blocking, the system comprising:

[0040] The signal acquisition module is configured to acquire the current signals on each branch circuit of the bus in real time.

[0041] An anomaly detection module is configured to calculate the current surge on the branch circuit and determine whether the current signal is abnormal based on the magnitude of the current surge.

[0042] The current direction function calculation module is configured to calculate the current direction function on the branch circuit when the current signal is in an abnormal state.

[0043] The fault direction determination module is configured to determine the fault direction of the current based on the current direction function;

[0044] The interlocking protection execution module is configured to determine the location of the fault point based on the fault direction of the current, and to perform interlocking protection on the circuit where the fault point is located.

[0045] Compared with the prior art, the present invention has at least the following technical effects:

[0046] This invention calculates the current surge on the branch circuit and determines whether the current signal is abnormal based on the magnitude of the current surge. When the current signal is determined to be in an abnormal state, the fault direction of the current is determined based on the current direction function, effectively overcoming the problem of traditional overcurrent protection being prone to false tripping or failure to trip due to distributed power source access. In addition, the use of a separate current direction function to determine the fault location solves the problem of protection failure when the bus voltage collapses. Finally, based on reliable direction information, instantaneous blocking or clearing of the fault is achieved. Its extremely high speed meets the rapid isolation requirements of active distribution networks to prevent cascading disconnection, thereby improving the safety and stability of the power grid. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating the low-voltage busbar protection method for distribution networks based on directional blocking in Embodiment 1 of the present invention. Detailed Implementation

[0048] The following description, in conjunction with schematic diagrams, illustrates a method and system for low-voltage busbar protection in a distribution network based on directional blocking, which represents a preferred embodiment of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0049] The invention is described more specifically by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0050] Example 1

[0051] Please refer to Figure 1 This embodiment discloses a method for protecting low-voltage busbars in a distribution network based on directional blocking, the method comprising:

[0052] S1. Real-time acquisition of current on the busbar and each branch circuit;

[0053] S2. Calculate the current surge on the branch circuit, and determine whether the current signal is abnormal based on the magnitude of the current surge;

[0054] S3. When it is determined that the current signal is in an abnormal state, the fault direction of the current is determined based on the current direction function;

[0055] S4. Determine the fault location based on the fault direction of the current, and construct a blocking logic based on the fault location.

[0056] In this embodiment, by calculating the current surge on the branch circuit and determining whether the current signal is abnormal based on the magnitude of the current surge, when the current signal is determined to be in an abnormal state, the fault direction of the current is determined based on the current direction function, effectively overcoming the problem of traditional overcurrent protection being prone to false tripping or failure to trip due to distributed power source access. In addition, the use of a separate current direction function to determine the fault location solves the problem of protection failure when the bus voltage collapses. Finally, based on reliable direction information, instantaneous blocking or clearing of the fault is achieved. Its extremely high speed meets the rapid isolation requirements of active distribution networks to prevent cascading disconnection, thereby improving the safety and stability of the power grid.

[0057] In a specific example of step S1, the system uses high-precision current transformers and analog-to-digital converters to acquire current signals from the busbar and each branch circuit in real time. The sampling frequency is set to above 10kHz to ensure that the data accuracy and time resolution meet the requirements of rapid protection. The transformation ratio of the current transformer can be selected according to the rated current of the system. For example, for a power distribution system with a rated current of 400A, a 400 / 5A transformer can be selected to ensure measurement accuracy. The analog-to-digital converter uses a resolution of 16 bits or higher to ensure the quality of small signal acquisition. For multi-branch busbar systems, each branch is equipped with an independent current measuring device, and the data is synchronously transmitted to the central processing unit through a communication network.

[0058] Furthermore, in step S2, calculating the current surge on the branch circuit includes:

[0059] The current surge on each branch circuit is calculated using a half-cycle differential algorithm.

[0060] The current surge is:

[0061] ;

[0062] in, Indicates the sudden change in current on the branch circuit described in the k-th clause; i k (t) represents the instantaneous current value on the branch circuit described in Article k at time t; T is a complete cycle of the alternating current.

[0063] The half-cycle differential algorithm calculates the abrupt change by comparing the current value at the current moment with the current value half a cycle ago. Specifically, it can be implemented by using a sliding time window to extract adjacent half-cycle data for differential operation. This algorithm shortens the data window length to half a cycle, reducing the amount of data required for the operation.

[0064] In this embodiment, the half-cycle differential algorithm only requires a data window of half a cycle, which can shorten the calculation delay to less than 10ms in the power frequency system. At the same time, it avoids the problem of phase reference inaccuracy caused by voltage drop, and is especially suitable for the rapid detection needs in the scenario of severe voltage drop in the early stage of low-voltage bus fault.

[0065] Furthermore, in step S2, determining whether the current signal is abnormal based on the magnitude of the current variable includes:

[0066] If the current surge is greater than or equal to the first set threshold, the current signal is determined to be in an abnormal state.

[0067] Wherein, the first set threshold is a multiple of the rated current.

[0068] In a specific example, the first set threshold can be set to 1.2 to 2 times the rated current, and can be flexibly adjusted according to system stability requirements and interference conditions to balance sensitivity and anti-interference capability.

[0069] Furthermore, if the current surge is less than or equal to the first set threshold, the current signal is determined to be normal.

[0070] In this embodiment, the current direction function is:

[0071] ;

[0072] Among them, i k (n) represents the nth discrete current sample value on the kth branch circuit, i ref (n) represents the nth discrete current sample value of the reference current; N represents the total number of data sample points used in a fault direction determination. This is the result of determining the direction of the current fault.

[0073] Wherein, the reference current i ref(n) The current signal is superimposed from the current signals of all branches on the bus except for the kth branch, which is used to characterize the overall current direction of the entire system except for the branch to be analyzed. Finally, by judging the product result, it is determined whether the current of the kth branch circuit is flowing into (forward) or flowing out (reverse) relative to the bus, thereby determining the fault location.

[0074] Specifically, after detecting a current anomaly, the system will continuously collect current data from multiple sampling points. For the current sampling sequence i of the k-th branch... k(n) The system synchronously acquires the reference current sequence i ref(n) When a branch circuit fails, the phase relationship between the current in that branch circuit and the currents in other branch circuits changes. This phase correlation can be reflected by calculating and summing the product sequences of the two. For example, if the first branch circuit fails, the reference current is the superposition of the currents in all other branches (such as branches 2, 3, and 4), i. ref(n) = i 2(n) + i 3(n) + i 4(n) By calculating i 1(n) with i ref(n) The dot product result can be used to determine the direction of the fault: if the result is positive, it indicates that the short-circuit current in the first branch circuit is in the same direction as the reference current, and the fault is located on the bus side; if the result is negative, it indicates that the current is in the opposite direction to the reference current, and the fault is located on the branch load side.

[0075] Furthermore, in this embodiment, determining the fault direction of the current based on the current direction function includes:

[0076] If D k If the value is 1, then the fault is located on the bus side and the current is in a positive fault state.

[0077] If D k =-1, then the fault is located on the load side of the branch circuit and the current is in a reverse fault state;

[0078] The positive fault state refers to the fault state that occurs when current flows into the busbar; the reverse fault state refers to the fault state that occurs when current flows out of the busbar.

[0079] In this embodiment, an adaptive direction criterion is constructed by using a current direction function. The polarity relationship between the branch circuit current and the reference current is used to replace the voltage phase comparison. Even under extreme conditions where the voltage signal is completely lost, the direction discrimination function can still be maintained, thus solving the core problem of the failure of the direction element caused by voltage drop.

[0080] Furthermore, determining the location of the fault point based on the fault direction of the current and providing blocking protection for the circuit where the fault point is located includes:

[0081] If the current fault direction of any of the branch circuits is positive, then the fault point is determined to be located in that branch circuit, and the bus protection is activated.

[0082] If the current fault direction of all the branch circuits is reversed, then the bus protection is blocked, and the protection of the branch circuits is performed.

[0083] In one specific embodiment, assuming a substation's low-voltage busbar connects to four branch circuits, when the second branch circuit detects a current surge exceeding a threshold and its direction function D2 = 1 (forward fault), while the direction functions of the other branches are all -1 (reverse fault), the system determines that the fault is located at the connection between the second branch and the busbar, and immediately activates the busbar protection device to perform a trip operation. Conversely, if all branch direction functions are -1, the fault is determined to be located on the branch load side. In this case, the busbar protection is blocked, and protection is only applied to the corresponding branch to avoid unnecessary busbar tripping.

[0084] Furthermore, the method also includes setting a three-level timing determination mechanism;

[0085] The first-level timing determination mechanism involves detecting the sudden change in current within 0-2 milliseconds.

[0086] The second-level timing determination mechanism is a criterion for confirming the direction of the current within 2-5 milliseconds;

[0087] The third-level timing determination mechanism completes the criterion fusion and trip signal output within 5-10 milliseconds.

[0088] Specifically, upon detecting a current surge exceeding a threshold, the first-level timing mechanism immediately activates, locking in the abnormal signal through high-speed sampling and calculation. Subsequently, the second-level timing mechanism performs secondary verification of the direction criterion, eliminating false alarms caused by voltage dips. Finally, the third-level timing mechanism combines the results of the first two levels; if the current direction is positive and the duration exceeds a set value, a trip signal is triggered. For example, if an abnormal current surge in a branch circuit is detected within 0-2 milliseconds, and the direction criterion stabilizes as positive within 2-5 milliseconds, the third-level timing mechanism completes the blocking logic judgment and outputs a trip signal within 5-10 milliseconds. The entire process can be completed within 10 milliseconds, significantly faster than the 20-50 millisecond response time of traditional protection systems.

[0089] Furthermore, the criterion fusion includes:

[0090] The criteria for the tripping condition are generated by combining the amplitude of the current surge, the criterion for the direction of the fault current, and the duration of the current surge.

[0091] The amplitude of the current surge refers to the instantaneous change in the current signal relative to the normal state. It can be calculated using a half-cycle differential algorithm and is used to determine the severity of the fault current. The criterion for the fault current direction involves logically determining the current flow direction using a direction function. Specifically, the sign of the product of the branch circuit current and the reference current can be used as the basis for differentiation between bus-side faults and branch load-side faults. The duration of the current surge refers to the length of time the abnormal current state persists. This can be recorded by a timer for durations exceeding a set threshold to eliminate misjudgments caused by transient interference.

[0092] In a specific example, when generating the tripping condition criterion, the amplitude requirement for the current surge is that the current surge in each branch circuit must continuously exceed a multiple of the rated current, for example, 1.2 times, and transient interference is eliminated through a sliding time window (e.g., 5ms). In practical implementation, the system uses a sliding time window of 5ms to continuously calculate the average value of the current surge within the window, avoiding misjudgments caused by sampling noise or transient disturbances. For short-term current surges caused by the startup of high-power equipment, since their duration is shorter than the preset sliding window, they will not be misjudged as a fault state by the system.

[0093] In another specific example, when generating the criterion for the tripping condition, the criterion for the fault current direction requires that at least one branch direction function D is used. k =1 (forward fault points to the bus), and there are no conflicting reverse criteria for other branches (to avoid misjudgment in multi-power supply scenarios). For example, if both branches A and B show a forward fault (D A =1,D B=1), the system will further determine the true fault location by comparing additional conditions such as the magnitude of their current surge amplitude and phase relationship.

[0094] In another specific example, when generating the tripping condition criterion, the duration of the current surge is required to be such that the surge exceeds the limit and lasts for at least 1 / 4 cycle. The time threshold is set based on statistical analysis of various disturbance signals, which reveals that the duration of most non-fault disturbances such as load switching and starting current is less than 5ms, while the duration of the actual fault current is significantly longer. Through this time criterion, the system can effectively avoid erroneous tripping caused by transient conditions such as load fluctuations and equipment startup.

[0095] Furthermore, by combining the amplitude of the current surge, the criterion for the direction of the fault current, and the duration of the current surge, the criteria for generating the tripping condition include:

[0096] When the duration of the current surge exceeds the time threshold, the current of one of the branch circuits is in a positive fault state, and the amplitude of the current surge exceeds the current threshold, a tripping operation is performed on the bus.

[0097] When the amplitude of the current change in multiple branch circuits exceeds the time threshold and the current is in a positive fault state, an emergency trip operation is performed on the bus.

[0098] Specifically, after detecting a current surge exceeding the current threshold, the system starts a timer to record the duration. If the duration reaches the time threshold, the system further combines directional criteria to locate the fault: when the current direction of a certain branch is positive, the fault is determined to be on the bus side, and the bus trip operation is immediately executed; if multiple branches simultaneously meet the requirements of exceeding the amplitude limit, positive direction, and duration, the fault is determined to be in the bus area, and an emergency trip is triggered to accelerate isolation.

[0099] The above method avoids misjudgments that may be caused by a single criterion by integrating three criteria: amplitude, direction, and time. For example, when the amplitude fluctuates due to the increased current from distributed power sources, the time threshold can filter out transient anomalies; when voltage drops cause ambiguity in the direction criterion, amplitude and time conditions can provide auxiliary verification.

[0100] In a specific example, the time threshold can be set to 5 milliseconds, and the current threshold can be set to 1.5 times the rated current. When a sudden change in current in a branch circuit is detected to exceed 1.5 times the rated current for more than 5 milliseconds, and the direction criterion is positive, the system determines that there is a fault on the bus side and performs a trip. If multiple branches meet the above conditions at the same time, an emergency trip mode is triggered, further shortening the circuit breaker operating time to a minimum (usually 3-5 milliseconds) to isolate the fault area as quickly as possible.

[0101] The time threshold can be dynamically adjusted according to the system's short-circuit capacity. For example, it can be shortened to 5 milliseconds in scenarios with high penetration of distributed power sources, while being extended to 8 milliseconds in traditional distribution networks. The current threshold can be corrected in real time according to load changes using an adaptive algorithm. For example, the recent average current can be calculated using a sliding window statistical method as a benchmark to ensure appropriate sensitivity and stability under various load conditions.

[0102] Example 2

[0103] This invention also provides a distribution network low-voltage busbar protection system based on directional blocking, employing the aforementioned distribution network low-voltage busbar protection method based on directional blocking, the system comprising:

[0104] The signal acquisition module is configured to acquire the current signals on each branch circuit of the bus in real time.

[0105] An anomaly detection module is configured to calculate the current surge on the branch circuit and determine whether the current signal is abnormal based on the magnitude of the current surge.

[0106] The current direction function calculation module is configured to calculate the current direction function on the branch circuit when the current signal is in an abnormal state.

[0107] The fault direction determination module is configured to determine the fault direction of the current based on the current direction function;

[0108] The interlocking protection execution module is configured to determine the location of the fault point based on the fault direction of the current, and to perform interlocking protection on the circuit where the fault point is located.

[0109] In one specific example, the signal acquisition module consists of a high-precision current transformer and a 16-bit analog-to-digital converter, with a sampling frequency of 20kHz, and can simultaneously monitor the current signals of up to 16 branches.

[0110] In another specific example, the anomaly detection module uses a high-performance DSP chip to implement the half-cycle differential algorithm, which has the ability to complete the calculation of the mutation within 2 milliseconds.

[0111] In another specific example, the current direction function calculation module is based on an FPGA platform and uses a parallel computing architecture to simultaneously process the direction discrimination of current signals from multiple branch circuits.

[0112] In another specific example, the fault direction determination module executes the direction criterion fusion logic through an embedded processor, which has anti-interference capability.

[0113] In another specific example, the interlocking protection execution module integrates a high-speed solid-state relay output unit with an action delay of less than 1 millisecond, which can directly control the circuit breaker trip coil.

[0114] Through the above technical solutions, this invention effectively solves the problems of protection maloperation and failure to operate caused by distributed power supply access. It avoids the failure of directional components caused by voltage drop by using pure current criterion for direction discrimination. It achieves millisecond-level response speed for fault detection and isolation by using a modular processing architecture. At the same time, it ensures the selectivity of protection actions by accurately executing the blocking logic and prevents the expansion of the fault range.

[0115] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A directional blocking based protection method for low voltage busbar in a power distribution network, characterized in that, The method comprises: real-time acquisition of current signals on the bus and each branch circuit; calculation of current mutation variables on the branch circuit, and determination of whether the current signal is abnormal based on the size of the current mutation variable; when it is determined that the current signal is in an abnormal state, determination of the fault direction of the current based on a current direction function; The current direction function is ; wherein, i k (n) is the nth discrete current sampling value on the kth branch circuit, i ref (n) represents the nth discrete current sampling value of the reference current; N represents the total number of data sample points used in the once-fault direction judgment; is the judgment result of the current fault direction; determination of the fault position based on the current fault direction, and construction of a blocking logic according to the fault position.

2. The directional blocking based protection method for a power distribution network low voltage bus according to claim 1, wherein, The calculation of the current mutation variable on the branch circuit comprises: using a half-cycle difference algorithm to calculate the current mutation variable on each branch circuit; the current mutation variable is: ； wherein, ik represents the current jump on the kth branch circuit; i k (t) represents the instantaneous current value on the kth branch circuit, T is one complete cycle of the alternating current.

3. The directional blocking based protection method for a power distribution network low voltage bus according to claim 2, wherein, the determination of whether the current signal is abnormal based on the size of the current mutation variable comprises: if the current mutation variable is greater than or equal to a first set threshold, it is determined that the current signal is in an abnormal state; wherein the first set threshold is a multiple of the rated current.

4. The directional blocking based protection method for a power distribution network low voltage bus according to claim 1, wherein, The determination of the fault direction of the current based on the current direction function comprises: If = 1, it is judged that the fault is located at the bus side and the current is in a forward fault state. If = -1, it is determined that the fault is located on the branch circuit load side, and the current is in a reverse fault condition. wherein the forward fault state refers to a fault state occurring when the current flows into the bus; and the reverse fault state refers to a fault state occurring when the current flows out of the bus.

5. The directional blocking based protection method for a power distribution network low voltage bus according to claim 4, wherein, The determination of the fault position based on the fault direction of the current, and the construction of a blocking logic according to the fault position comprise: if the current fault direction of any branch circuit is forward, it is determined that the fault point is located in the branch circuit, and the bus protection is started; if the current fault direction of all branch circuits is reverse, the bus protection is blocked, and the protection of the branch circuit is performed.

6. The directional lock based protection method for a power distribution network low voltage bus according to any of claims 1-5, characterized in that, The method further comprises setting a three-level time sequence determination mechanism; wherein the first-level time sequence determination mechanism is to perform detection of the current mutation variable within 0-2 milliseconds; the second-level time sequence determination mechanism is to confirm the criterion of the current direction within 2-5 milliseconds; the third-level time sequence determination mechanism is to complete criterion fusion and output of a trip signal within 5-10 milliseconds.

7. The directional blocking based protection method for a power distribution network low voltage bus as claimed in claim 6, wherein, The criterion fusion comprises: combining the amplitude of the current mutation variable, the criterion of the fault current direction, and the duration of the current mutation to generate a criterion of a trip condition.

8. The directional blocking based protection method for a power distribution network low voltage bus according to claim 7, wherein, The generation of the criterion of the trip condition by combining the amplitude of the current mutation variable, the criterion of the fault current direction, and the duration of the current mutation comprises: when the duration of the current mutation exceeds a time threshold, the current of one branch circuit is in a forward fault state, and the amplitude of the current mutation variable exceeds a current threshold, a trip operation is performed on the bus; when the amplitudes of the currents of multiple branch circuits exceed a time threshold, and the currents are all in a forward fault state, an emergency trip operation is performed on the bus.

9. A directional blocking based protection system for a low voltage bus of a power distribution network, characterized in that, The system comprises: a signal acquisition module configured to acquire current signals on each branch circuit on the bus in real time; an abnormality determination module configured to calculate current mutation variables on the branch circuit, and determine whether the current signal is abnormal based on the size of the current mutation variable; a current direction function calculation module configured to calculate a current direction function on the branch circuit when the current signal is in an abnormal state; The current direction function is ; wherein, i k (n) is the nth discrete current sample value on the kth branch circuit, i ref (n) represents the nth discrete current sample value of the reference current; N represents the total number of data sample points used in the once-fault direction judgment; is the judgment result of the current fault direction; a fault direction determination module configured to determine the fault direction of the current based on the current direction function; and a criterion fusion module configured to combine the amplitude of the current mutation variable, the criterion of the fault current direction, and the duration of the current mutation to generate a criterion of a trip condition. The lockout protection execution module is configured to determine the location of the fault point based on the fault direction of the current, and perform lockout protection on the circuit where the fault point is located.

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