Capacitor bank short-circuit fault protection method and related device

Abstract

The invention relates to the technical field of power electronic devices, in particular to a capacitor bank short-circuit fault protection method and a related device. The method comprises the following steps: acquiring unbalanced current of a neutral line and bus voltage of each phase of a three-phase bus; determining a first phase of the unbalanced current and a second phase of each bus voltage; determining a fault branch and a target bus connected with the fault branch according to the first phase and each second phase; obtaining the capacitance value and the total number of capacitors in the fault branch and the voltage of the target bus; according to the capacitance value, the total number of the capacitors, the voltage of the target bus and the unbalanced current, the number of the fault capacitors in the fault branch is calculated, the technical problem that the number of the fault capacitors is difficult to determine in existing unbalanced current protection is solved, and data support is provided for achieving the inverse time limit characteristic of a relay protection device.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic devices, and in particular, to a short - circuit fault protection method for a capacitor bank and related devices. Background Art

[0002] Existing substations include buses and equipment of low - voltage levels (such as 10 kV), which usually adopt delta connection and are set on the low - voltage side of the substation. Generally, a capacitor bank (such as a shunt capacitor bank) is installed on the low - voltage side of the substation to achieve functions such as reactive power compensation, improving the bus voltage quality, and reducing power loss.

[0003] Specifically, the shunt capacitor bank usually adopts star connection, such as a common three - phase capacitor bank with double - star connection. One end of the two three - phase capacitor banks with double - star connection is connected to the bus, and the neutral points of the two three - phase capacitor banks are connected through a neutral line. In this connection structure, when a short - circuit fault such as a short - circuit or short - circuit occurs in the capacitors inside the capacitor bank, an unbalanced current is generated in the neutral line of the capacitor bank, resulting in an unbalanced operation state of the three - phase capacitor bank. If it is in an unbalanced operation state for a long time, it is easy to damage the capacitors in the capacitor bank and bring risks of safety accidents. Therefore, the existing technology adopts unbalanced current protection to protect the capacitor bank in an unbalanced operation state.

[0004] The existing unbalanced current protection is to trip the circuit breaker connecting the capacitor bank and the bus when the unbalanced current reaches a certain value and lasts for a period of time. However, with this protection method, it is difficult to determine the number of faulty capacitors. Summary of the Invention

[0005] The present invention provides a short - circuit fault protection method for a capacitor bank and related devices to solve the technical problem that it is difficult to determine the number of faulty capacitors in the existing unbalanced current protection.

[0006] On the one hand, the present invention provides a short - circuit fault protection method for a capacitor bank. The capacitor bank includes a shunt capacitor bank, and the shunt capacitor bank includes two capacitor series branches. Each capacitor series branch includes at least one capacitor. One end of each shunt capacitor bank is connected to each phase of the three - phase bus in one - to - one correspondence, and the other end of each shunt capacitor bank is connected to the neutral line. The method includes:

[0007] Obtain the unbalanced current of the neutral line and the phase - bus voltages of each phase of the three - phase bus;

[0008] Determine the first phase of the unbalanced current and the second phases of the bus voltages;

[0009] Determine the faulty branch and the target bus connected to the faulty branch according to the first phase and the second phases;

[0010] Obtain the capacitance value and total number of capacitors in the faulty branch, and the voltage of the target bus;

[0011] Calculate the number of faulty capacitors in the faulty branch according to the capacitance value, the total number of capacitors, the voltage of the target bus, and the unbalanced current.

[0012] Optionally, the method further includes:

[0013] Obtain the fault current of the faulty branch, the equivalent resistance of the faulty branch, and the heat setting value;

[0014] Calculate the fault operation time according to the amplitude of the fault current, the equivalent resistance, and the heat setting value;

[0015] Update the fault operation time to the relay protection operation time of the relay protection device.

[0016] Optionally, the determining the faulty branch and the target bus connected to the faulty branch according to the first phase and each of the second phases includes:

[0017] Calculate the phase difference between each of the second phases and the first phase respectively;

[0018] Determine the phase relationship between each of the second phases and the first phase according to each of the phase differences;

[0019] Determine the faulty branch and the target bus connected to the faulty branch according to the phase relationship.

[0020] Optionally, the calculating the fault operation time according to the amplitude of the fault current, the equivalent resistance, and the heat setting value includes:

[0021] Calculate the product of the square of the amplitude of the fault current and the equivalent resistance;

[0022] Calculate the ratio of the heat setting value to the product to obtain the fault operation time.

[0023] On the other hand, the present invention also provides a capacitor bank short-circuit fault protection device. The capacitor bank includes a shunt capacitor bank. The shunt capacitor bank includes two capacitor series branches. Each capacitor series branch includes at least one capacitor. One end of each shunt capacitor bank is connected to the three-phase bus in one-to-one correspondence, and the other end of each shunt capacitor bank is connected to the neutral line. The device includes:

[0024] A first obtaining module, configured to obtain the unbalanced current of the neutral line and the phase bus voltages of the three-phase bus;

[0025] A first determination module, configured to determine a first phase of the unbalanced current and a second phase of each of the bus voltages;

[0026] A second determination module, configured to determine a faulty branch and a target bus to which the faulty branch is connected according to the first phase and each of the second phases;

[0027] A second acquisition module, configured to acquire a capacitance value and a total number of capacitors in the faulty branch, and a voltage of the target bus;

[0028] A first calculation module, configured to calculate a number of faulty capacitors in the faulty branch according to the capacitance value, the total number of capacitors, the voltage of the target bus, and the unbalanced current.

[0029] Optionally, the apparatus further includes:

[0030] A third acquisition module, configured to acquire a fault current in the faulty branch, an equivalent resistance of the faulty branch, and a heat setting value;

[0031] A second calculation module, configured to calculate a fault action time according to an amplitude of the fault current, the equivalent resistance, and the heat setting value;

[0032] An update module, configured to update the fault action time to a relay protection action time of a relay protection device.

[0033] Optionally, the second determination module includes:

[0034] A first calculation unit, configured to calculate a phase difference between each of the second phases and the first phase respectively;

[0035] A first determination unit, configured to determine a phase relationship between each of the second phases and the first phase according to each of the phase differences;

[0036] A second determination unit, configured to determine the faulty branch and the target bus to which the faulty branch is connected according to the phase relationship.

[0037] Optionally, the second calculation module includes:

[0038] A second calculation unit, configured to calculate a product of a square of an amplitude of the fault current and the equivalent resistance;

[0039] A third calculation unit, configured to calculate a ratio of the heat setting value to the product to obtain the fault action time.

[0040] On the other hand, the present invention provides an electronic device, which includes a processor and a memory;

[0041] The memory is used to store program code and transfer the program code to the processor;

[0042] The processor is used to execute the method as described above according to the instructions in the program code.

[0043] On the other hand, the present invention provides a computer-readable storage medium for storing program code for executing the method as described above.

[0044] It can be seen from the above technical solutions that the present invention has the following advantages:

[0045] The present invention provides a method for protecting a capacitor bank from short-circuit faults. The capacitor bank includes a shunt capacitor bank, the shunt capacitor bank includes two capacitor series branches, each capacitor series branch includes at least one capacitor, one end of each shunt capacitor bank is connected to the three-phase bus respectively, and the other end of each shunt capacitor bank is connected to the neutral line. The method includes: obtaining the unbalanced current of the neutral line and the phase bus voltages of the three-phase bus; determining the first phase of the unbalanced current and the second phases of the bus voltages; determining the fault branch and the target bus to which the fault branch is connected according to the first phase and the second phases; obtaining the capacitance value and the total number of capacitors in the fault branch, and the voltage of the target bus; calculating the number of faulty capacitors in the fault branch according to the capacitance value, the total number of capacitors, the voltage of the target bus and the unbalanced current.

[0046] In the present invention, by obtaining the unbalanced current of the neutral line and the phase bus voltages of the three-phase bus; determining the first phase of the unbalanced current and the second phases of the bus voltages; determining the fault branch and the target bus to which the fault branch is connected according to the first phase and the second phases, the positioning of the short-circuit fault is realized, so that in practical applications, the time for fault positioning is reduced and the fault screening efficiency is improved; and by obtaining the capacitance value and the total number of capacitors in the fault branch, and the voltage of the target bus; calculating the number of faulty capacitors in the fault branch according to the capacitance value, the total number of capacitors, the voltage of the target bus and the unbalanced current, the calculation of the number of faulty capacitors is realized, and the technical problem that it is difficult to determine the number of faulty capacitors by the existing unbalanced current protection is solved, providing data support for realizing the inverse time characteristic of the relay protection device. Description of the Drawings

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0048] Figure 1 It is a step flow chart of a capacitor bank short - circuit fault protection method provided by an embodiment of the present invention;

[0049] Figure 2 It is a schematic circuit structure diagram of a shunt capacitor bank provided by an embodiment of the present invention;

[0050] Figure 3 It is a simplified diagram of each branch of the shunt capacitor bank provided by an embodiment of the present invention;

[0051] Figure 4 It is a simplified diagram of each phase of the shunt capacitor bank provided by an embodiment of the present invention;

[0052] Figure 5 It is a step flow chart of a capacitor bank short - circuit fault protection method provided by another embodiment of the present invention;

[0053] Figure 6 It is a structural block diagram of a capacitor bank short - circuit fault protection device provided by an embodiment of the present invention. Detailed implementation manners

[0054] In the actual operation of a substation, sometimes the capacitors of a shunt capacitor bank need to have a relatively high voltage level. Inside the shunt capacitor bank, when the withstand voltage of a single capacitor is not sufficient to meet the voltage level requirement, multiple capacitors can be connected in series to form a capacitor series branch, and multiple capacitor series branches are connected in parallel to form a shunt capacitor bank, thereby improving the overall voltage - bearing capacity. In this structure, the capacitors in the capacitor series branch may experience short - circuit faults such as short - circuit or short - connection, resulting in an unbalanced operation state of the shunt capacitor bank. Therefore, it is necessary to analyze the resulting neutral - line unbalanced current to better protect the capacitor bank.

[0055] The existing neutral line unbalanced current protection considers that when multiple capacitors are removed, current flows through the neutral line and causes the protection to operate. However, the unbalanced current protection in the prior art only disconnects the circuit breaker connecting the capacitor bank to the bus voltage after the unbalanced current reaches a certain value and lasts for a certain period of time. This simple disconnection method does not have the function of estimating the number of faulty capacitors in the short-circuit branch; secondly, it does not have the function of locating the short-circuit fault, that is, it cannot locate which branch has a fault; finally, the relay protection operation time of the relay protection device in the prior art is a constant value and cannot be flexibly adjusted according to the number of faulty capacitors, resulting in the time setting value of its unbalanced current not having an inverse time characteristic. As a result, the existing unbalanced current protection does not consider the problem of the remaining normal capacitors heating up during a short circuit, and it is difficult to avoid the situation where the normal capacitors are severely heated and damaged.

[0056] To solve the above technical problems, the present invention mainly provides the following technical solutions:

[0057] The present invention determines the faulty branch where the short-circuit fault occurs through the phase relationship between the unbalanced current and the three-phase AC bus voltage, quickly locates the fault, saves the fault screening time, and calculates the number of faulty capacitors by using the bus voltage, unbalanced current, capacitance value, and total number of capacitors corresponding to the faulty branch, thereby realizing the determination of the number of faulty capacitors. For the time when the relay protection device operates to disconnect the corresponding circuit breaker due to the unbalanced current in the capacitor bank, a corresponding setting principle is proposed, which can make it have an inverse time characteristic. Furthermore, when a short-circuit fault occurs in a certain branch of the capacitor bank and the number of faulty capacitors is large, the operation time of the protection device is shortened, and the relevant circuit breaker is quickly disconnected to ensure that the remaining capacitors that do not have a short circuit will not be severely heated and damaged.

[0058] In order to make the invention purpose, features, and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0059] It should be noted that the capacitor bank involved in the embodiments of the present invention includes a shunt capacitor bank. The shunt capacitor bank includes two capacitor series branches. Each capacitor series branch includes at least one capacitor. One end of each shunt capacitor bank is correspondingly connected to the three-phase bus, and the other end of each shunt capacitor bank is connected to the neutral line. In one example, a current transformer is provided on the neutral line for collecting the neutral line unbalanced current.

[0060] Specifically, a circuit breaker is provided on each phase bus, and is connected to the corresponding shunt capacitor bank through the circuit breaker. The three-phase bus can adopt a delta connection method. Among them, the voltage level of the three-phase bus can be 10 kV. The number of capacitors in the capacitor series branch can be selected according to the actual situation. When there are multiple capacitors in the capacitor series branch, the connection relationship between the capacitors is series connection.

[0061] In the embodiment of the present invention, a case where each phase bus is connected to a group of shunt capacitor banks, each group of shunt capacitor banks includes two capacitor series branches, and each capacitor series branch is provided with multiple capacitors is taken as an example for detailed description. As Figure 2 shown in the shunt capacitor structure including single-phase series capacitors, where , , are three-phase symmetrical AC voltages with delta connection, usually 10 kV voltage level. The voltage of phase A is connected to the circuit breaker of phase A, and then connected to two capacitor series branches, which are divided into the first capacitor series branch and the second capacitor series branch. The first capacitor series branch includes n capacitors connected in series, which are respectively , , …, , and the capacitance value of each capacitor is , defined as branch A1. Among them, the capacitor is connected to the circuit breaker of phase A, and one end of the capacitor is connected to . The second capacitor series branch includes n capacitors connected in series, which are respectively , , …, , and the capacitance value of each capacitor is , defined as branch A2. Among them, the capacitor is connected to the circuit breaker of phase A, and one end of the capacitor is connected to .

[0062] The voltage of phase B is connected to the circuit breaker of phase B and then connected to two capacitor series branches. The first capacitor series branch includes n capacitors connected in series, which are respectively , , …, , and the capacitance value of each capacitor is , defined as branch B1. Among them, the capacitor is connected to the circuit breaker of phase B, and one end of the capacitor is connected to . The second capacitor series branch includes n capacitors connected in series, which are respectively , , …, , the capacitance value of each capacitor is , defined as the B2 branch, where the capacitor is connected to the B-phase circuit breaker, and one end of the capacitor is connected to .

[0063] The C-phase voltage is connected to the C-phase circuit breaker, and then connected to two series capacitor branches. The first series capacitor branch includes n series capacitors, which are respectively , , …, , the capacitance value of each capacitor is , defined as the C1 branch, where the capacitor is connected to the C-phase circuit breaker, and one end of the capacitor is connected to ; The second series capacitor branch includes n series capacitors, which are respectively , , …, , defined as the C2 branch, where the capacitor is connected to the C-phase circuit breaker, and one end of the capacitor is connected to . is the neutral point of the three series capacitor branches A1, B1, and C1, is the neutral point of the three series capacitor branches A2, B2, and C2.

[0064] The current transformer has one end connected to , and the other end connected to . The current flowing through the current transformer is the unbalanced current (i.e., the unbalanced current of the neutral line in the present invention), and the reference direction is from flowing to as the positive direction, and its value is 0 during normal operation. For , , The two capacitor groups connected to each of them, because they are connected in series inside, it is very easy for them to have short-circuit faults such as capacitor short circuit or short connection. When a short-circuit fault occurs, it will cause the generation of unbalanced current, that is is not 0.

[0065] Please refer to Figure 1 , the following introduces a capacitor bank short-circuit fault protection method provided by an embodiment of the present invention. This embodiment mainly includes:

[0066] 101. Obtain the unbalanced current of the neutral line and the phase bus voltages of the three-phase bus.

[0067] It should be noted that the unbalanced current on the neutral line can be collected by setting up a current collection device, and the phase voltages of phase A bus, phase B bus, and phase C bus can be collected respectively by setting up a voltage collection device. The current collection device and the voltage collection device can be selected according to the actual situation, and are not limited in this embodiment.

[0068] 102. Determine the first phase of the unbalanced current and the second phases of the respective bus voltages.

[0069] It should be noted that by performing phase analysis on the unbalanced current and the respective bus voltages, the phase of the unbalanced current (i.e., the first phase) and the phases of the phase voltages of each phase (i.e., the second phases) are obtained.

[0070] 103. Determine the faulty branch and the target bus to which the faulty branch is connected according to the first phase and the respective second phases.

[0071] It should be noted that the respective second phases are compared with the first phase in terms of phase to determine the phase relationship between the respective second phases and the first phase, and the series capacitor branch where the fault occurs (i.e., the faulty branch) is determined respectively according to each phase relationship. Then, according to the connection structure of the faulty branch, the bus connected to the faulty branch is determined as the target bus.

[0072] 104. Obtain the capacitance value of the capacitor in the faulty branch, the total number of capacitors, and the voltage of the target bus.

[0073] It should be noted that the capacitance value of each capacitor in the series capacitor branch is the same value. Therefore, the capacitance value of one of the capacitors is obtained in this step. The voltage of the target bus refers to the three-phase symmetrical AC voltage of the target bus.

[0074] 105. Calculate the number of faulty capacitors in the faulty branch according to the capacitance value, the total number of capacitors, the voltage of the target bus, and the unbalanced current.

[0075] It should be noted that there is a correlation between the number of faulty capacitors and the capacitance value of the capacitor, the total number of capacitors, the voltage of the target bus, and the unbalanced current. Therefore, by using the capacitance value of the capacitor, the total number of capacitors, the voltage of the target bus, and the unbalanced current for calculation, the number of faulty capacitors can be obtained.

[0076] In one example, after equivalently simplifying the structure of the shunt capacitor bank, the node voltage method and Kirchhoff's current law are used to analyze each series capacitor branch in the equivalent structure respectively, and expressions for the capacitance value of the capacitor in the series capacitor branch, the total number of capacitors, the three-phase unbalanced AC voltage of the bus connected to the series capacitor branch, the unbalanced current, and the number of faulty capacitors can be obtained. These expressions reflect the correlation between the capacitance value of the capacitor in the series capacitor branch, the total number of capacitors, the three-phase unbalanced AC voltage of the bus connected to the series capacitor branch, the unbalanced current, and the number of faulty capacitors. Therefore, when it is determined that a short-circuit fault occurs in a certain series capacitor branch, the number of corresponding faulty capacitors can be calculated through the capacitance value of the capacitor, the total number of capacitors, the voltage of the target bus, and the unbalanced current.

[0077] As can be seen from the above, in this embodiment, by obtaining the unbalanced current of the neutral line and the phase voltages of each phase of the three-phase bus; determining the first phase of the unbalanced current and the second phase of each bus voltage; and determining the faulty branch and the target bus connected to the faulty branch according to the first phase and each second phase, the location of the short-circuit fault is achieved. Thus, in practical applications, the time for fault location is reduced and the fault screening efficiency is improved; and by obtaining the capacitance value of the capacitor and the total number of capacitors in the faulty branch, and the voltage of the target bus; calculating the number of faulty capacitors in the faulty branch according to the capacitance value, the total number of capacitors, the voltage of the target bus, and the unbalanced current, the calculation of the number of faulty capacitors is realized, solving the technical problem that it is difficult for the existing unbalanced current protection to determine the number of faulty capacitors, and providing data support for realizing the inverse time characteristic of the relay protection device.

[0078] In a specific embodiment, step 103 includes:

[0079] S31. Calculate the phase difference between each second phase and the first phase respectively;

[0080] S32. Determine the phase relationship between each second phase and the first phase according to each phase difference;

[0081] S33. Determine the faulty branch and the target bus connected to the faulty branch according to the phase relationship.

[0082] It should be noted that the phase relationship includes leading by 90° or lagging by 90°. In this embodiment, the phase difference between the phase of the A-phase bus voltage and the first phase is calculated, the phase difference between the phase of the B-phase bus voltage and the first phase is calculated, and the phase difference between the phase of the C-phase bus voltage and the first phase is calculated. The phase relationship between each phase bus voltage and the unbalanced current is determined according to the phase difference, and the corresponding faulty branch and the target bus connected to the faulty branch are determined according to the phase relationship.

[0083] According to the foregoing embodiments, the A-phase busbar, the B-phase busbar, and the C-phase busbar are respectively connected to a shunt capacitor bank, and each shunt capacitor bank includes a first capacitor series branch and a second capacitor series branch. Each first capacitor series branch is connected to the same neutral point (i.e., the first neutral point), and each second capacitor series branch is connected to another neutral point (the second neutral point), where both neutral points are located on the same neutral line.

[0084] Among them, it can be defined that the reference direction of the unbalanced current is positive from the first neutral point to the second neutral point. Or, the reference direction of the unbalanced current is defined as positive from the second neutral point to the first neutral point. Taking the direction from the first neutral point to the second neutral point as the positive direction as an example in this embodiment, the steps for determining the faulty branch and the target busbar are described as follows:

[0085] When the first phase leads the phase of the A-phase busbar voltage by 90°, it indicates that a fault occurs in the first capacitor series branch connected to the A-phase busbar. Then, the first capacitor series branch connected to the A-phase busbar is the faulty branch, and the A-phase busbar is the target busbar; when the first phase lags the phase of the A-phase busbar voltage by 90°, it indicates that a fault occurs in the second capacitor series branch connected to the A-phase busbar. Then, the second capacitor series branch connected to the A-phase busbar is the faulty branch, and the A-phase busbar is the target busbar.

[0086] When the first phase leads the phase of the B-phase busbar voltage by 90°, it indicates that a fault occurs in the first capacitor series branch connected to the B-phase busbar. Then, the first capacitor series branch connected to the B-phase busbar is the faulty branch, and the B-phase busbar is the target busbar; when the first phase lags the phase of the B-phase busbar voltage by 90°, it indicates that a fault occurs in the second capacitor series branch connected to the B-phase busbar. Then, the second capacitor series branch connected to the B-phase busbar is the faulty branch, and the B-phase busbar is the target busbar.

[0087] When the first phase leads the phase of the C-phase busbar voltage by 90°, it indicates that a fault occurs in the first capacitor series branch connected to the C-phase busbar. Then, the first capacitor series branch connected to the C-phase busbar is the faulty branch, and the C-phase busbar is the target busbar; when the first phase lags the phase of the C-phase busbar voltage by 90°, it indicates that a fault occurs in the second capacitor series branch connected to the C-phase busbar. Then, the second capacitor series branch connected to the C-phase busbar is the faulty branch, and the C-phase busbar is the target busbar.

[0088] It can be understood that when the reference direction of the unbalanced current is defined as positive from the second neutral point to the first neutral point, the fault location judgment criterion is opposite to that when the reference direction of the unbalanced current is defined as positive from the first neutral point to the second neutral point. Taking the A-phase bus as an example, when the reference direction of the unbalanced current is defined as positive from the second neutral point to the first neutral point, if the first phase leads the phase of the A-phase bus voltage by 90°, it indicates that the fault occurs on the second capacitor series branch connected to the A-phase bus, then the second capacitor series branch connected to the A-phase bus is the fault branch, and the A-phase bus is the target bus; if the first phase lags the phase of the A-phase bus voltage by 90°, it indicates that the fault occurs on the first capacitor series branch connected to the A-phase bus, then the first capacitor series branch connected to the A-phase bus is the fault branch, and the A-phase bus is the target bus.

[0089] In an application example, in combination with Figure 2 the structure shown, the principle of a capacitor bank short-circuit fault protection method provided by an embodiment of the present invention will be described.

[0090] Taking Figure 2 the A2 branch in (i.e., , ...) as an example of a short-circuit fault occurring, assuming that among the n capacitors connected in series in the A2 branch, k capacitors are short-circuited or short-connected, then the equivalent capacitance of the A2 branch is:

[0091] .

[0092] The capacitors in other branches operate normally, and the equivalent capacitance value is as shown in Equation (1).

[0093] (1)

[0094] Therefore, Figure 2 the circuit of Figure 3 can be equivalently represented as

[0095] Furthermore, according to Figure 3 the structure shown, ignoring the current transformer and considering it in a short-circuited state, then Figure 3 the structure shown can be further simplified to Figure 4 the structure shown.

[0096] Figure 4 In , is the equivalent capacitance of the A phase, and its value is , and the impedance is is the equivalent capacitance of the B phase, and its value is , and the impedance is , is the equivalent capacitance of C, and its value is , and the impedance is , and are combined into point N, and its voltage is .

[0097] Using the node voltage method, the equations can be listed as shown in Equation (2).

[0098] (2)

[0099] It can be obtained that the voltage of point N is

[0100] (3)

[0101] Since the current transformer is regarded as a short circuit, therefore and the voltages at points are the same as the voltage at point N, both being Figure 3 . Therefore, according to

[0102] (4)

[0103] From Equation (4), it can be seen that when a short circuit fault occurs in branch A2, the phase of and the phase of exactly differ by 90°, that is . Similarly, according to the same method, the expression of the unbalanced current when short circuits occur in branches A1, B1, C1, B2, and C2 respectively can be deduced.

[0104] When a short circuit occurs in branch A1, as shown in Equation (5).

[0105] (5)

[0106] At this time, .

[0107] When a short circuit occurs in branch B1, as shown in Equation (6).

[0108] (6)

[0109] At this time, .

[0110] When a short circuit occurs in branch C1, As shown in formula (7).

[0111] (7)

[0112] at this time, .

[0113] When the B2 branch is short-circuited, As shown in formula (8).

[0114] (8)

[0115] at this time, .

[0116] When C2 branch short circuit occurs, As shown in formula (9).

[0117] (9)

[0118] at this time, .

[0119] Based on the above, it can be known that when a short circuit occurs in the capacitors in the series branches of different capacitors, the unbalanced current Phase , and compared with the phase of each phase bus voltage, according to the comparison result, it can be determined which branch the short circuit fault occurred. As shown in Table 1, if it is detected Ahead of the times The angle is , it indicates that the capacitor in the A1 branch is short-circuited. Ahead of the times The angle is , it indicates that the capacitor in branch B1 is short-circuited. Ahead of the times The angle is , it indicates that the capacitor in the C1 branch is short-circuited. Hysteresis The angle is , it indicates that the capacitor in the A2 branch is short-circuited. Hysteresis The angle is , the capacitor in branch B2 is short-circuited. Hysteresis The angle is , it indicates that the capacitor in the C2 branch is short-circuited.

[0120] Table 1

[0121]

[0122] Based on the above formulas (4)-(9), the formula for calculating the number of faulty capacitors is shown in formula (10).

[0123] (10)

[0124] represents the modulus value of represents the modulus value of is the number of faulty capacitors in the faulty branch is the three-phase symmetrical AC voltage of the target bus connected to the faulty branch is the total number of capacitors in the faulty branch

[0125] Therefore, after determining the capacitor series branch where a short-circuit fault occurs, the number of faulty capacitors in the faulty branch can be calculated based on the capacitance value, the total number of capacitors, the voltage of the target bus, and the unbalanced current.

[0126] Please refer to Figure 5 , a method for protecting a capacitor bank from short-circuit faults provided by an embodiment of the present invention includes:

[0127] 201. Obtain the unbalanced current of the neutral line and the phase bus voltages of the three-phase busbars;

[0128] 202. Determine the first phase of the unbalanced current and the second phase of each bus voltage;

[0129] 203. Determine the faulty branch and the target bus connected to the faulty branch according to the first phase and each second phase;

[0130] 204. Obtain the capacitance value and the total number of capacitors in the faulty branch, and the voltage of the target bus;

[0131] 205. Calculate the number of faulty capacitors in the faulty branch according to the capacitance value, the total number of capacitors, the voltage of the target bus, and the unbalanced current.

[0132] It should be noted that steps 201 to 205 can refer to steps 101 to 105, which will not be elaborated here.

[0133] 206. Obtain the fault current of the faulty branch, the equivalent resistance of the faulty branch, and the heat setting value.

[0134] It should be noted that the fault current refers to the current flowing through the capacitors that have not failed in the faulty branch. When a fault occurs in a capacitor series branch, the current of the capacitor series branch itself is the current of the capacitors that have not failed. In one example, the fault current of the capacitor series branch can be collected by using a current acquisition device.

[0135] The equivalent resistance of the faulty branch refers to the equivalent resistance of the capacitor, which is regarded as a constant value. The heat setting value is a constant, which can be set according to the actual situation.

[0136] 207. Calculate the fault operation time based on the amplitude of the fault current, the equivalent resistance, and the heat setting value.

[0137] It should be noted that the fault operation time has a correlation with the amplitude of the fault current, the equivalent resistance, and the heat quantity. Therefore, the fault operation time can be calculated using the amplitude of the fault current, the equivalent resistance, and the heat setting value. And the fault operation time is negatively correlated with the number of faulty capacitors.

[0138] 208. Update the fault operation time to the relay protection operation time of the relay protection device.

[0139] It should be noted that the relay protection operation time refers to the time when the relay protection operates to cut off the circuit breaker of the capacitor bank.

[0140] In this step, by updating the fault operation time to the relay protection operation time of the relay protection device, the relay protection operation time of the relay protection device can be flexibly adjusted according to the number of faulty capacitors. Moreover, since the fault operation time is negatively correlated with the number of faulty capacitors, that is, when the number of faults increases, the fault operation time becomes shorter, enabling the relay protection device to have an inverse time characteristic. Thus, when the number of faulty capacitors is large, the corresponding circuit breaker can be timely tripped to stop the operation of the capacitors, avoiding the situation where the non-faulty capacitors are severely heated and damaged.

[0141] Therefore, in the method provided in this embodiment, by obtaining the fault current of the faulty branch, the equivalent resistance of the faulty branch, and the heat setting value, calculating the fault operation time based on the amplitude of the fault current, the equivalent resistance, and the heat setting value, and updating the fault operation time to the relay protection operation time of the relay protection device, the relay protection device's operation time for cutting off faults has an inverse time characteristic, and can adjust the operation time according to the number of capacitors. Thus, when the number of faulty capacitors is large, the operation time is shortened to quickly cut off the fault, avoiding the situation where the non-faulty capacitors are severely heated and damaged, and reducing the loss of the capacitors.

[0142] In a specific embodiment, step 207 includes the following sub-steps:

[0143] S71. Calculate the product of the square of the amplitude of the fault current and the equivalent resistance;

[0144] S72. Calculate the ratio of the heat setting value to the product to obtain the fault operation time.

[0145] It should be noted that the mathematical expression of the fault operation time is as follows:

[0146] (11)

[0147] Wherein, is the fault operation time, is the heat setting value, is the equivalent resistance, is the fault current amplitude.

[0148] In an application example, in combination with the structure shown in Figure 2 , the principles of steps 206 to 208 will be described in detail.

[0149] According to Figure 2 the shown circuit structure, when a short - circuit fault occurs in the capacitor of a certain series - capacitor branch, not only will change, but also the current flowing through each series - capacitor branch, that is, , , , , , will also change.

[0150] Taking the short - circuit fault of branch A2 as an example, the current flowing through each branch at this time is as shown in Equation (12).

[0151] (12)

[0152] According to the analysis of the foregoing application example, the other expressions of , are as shown in Equation (13):

[0153] (13)

[0154] From Equation (13), it can be obtained that . In addition, since , and Equation (14) holds at this time, therefore, Equation (15) holds.

[0155] (14)

[0156] (15)

[0157] From Equation (13), it is easy to obtain: , so as k increases, also increases.

[0158] In addition, by comparing and , Equation (16) can be obtained.

[0159] (16)

[0160] From Equation (16), it can be obtained that , combined with Equation (15), Equation (17) can be obtained.

[0161] (17)

[0162] From Equation (17), it can be seen that when a partial capacitance short circuit occurs in the A2 branch, the current in the A2 branch has the maximum amplitude among the amplitudes of the currents in each branch. In addition, Corollary 2 can be obtained: when short circuits occur in the A1, A2, B1, B2, C1, and C2 branches respectively, , , , , , are respectively the maximum values among the amplitudes of the currents in each branch, and the current flowing through each short-circuited branch increases with the increase of k. In actual situations, capacitors all contain equivalent resistances. Let the equivalent resistance of each capacitor in each parallel capacitor bank be . When current flows through the capacitor, energy loss and heat generation will occur in its equivalent resistance.

[0163] Suppose there are k capacitors in a certain branch that have a short-circuit fault, and the current in this branch with the short-circuit fault is (when a short circuit occurs in the A1 branch , when a short circuit occurs in the A2 branch , when a short circuit occurs in the B1 branch , when a short circuit occurs in the B2 branch , when a short circuit occurs in the C1 branch , when a short circuit occurs in the C2 branch ), and the short-circuit time is (that is, the time when the relay protection operates to cut off the capacitor bank circuit breaker), then during this period, on this short-circuited branch, for the remaining n - k capacitors that have not short-circuited, the heat generated on their equivalent resistances can be estimated as shown in Equation (18):

[0164] (18)

[0165] According to Equation (17), Equation (18), and Corollary 2, it can be known that when Figure 2 a short circuit of k capacitors occurs in a certain branch, then on all the non-short-circuited capacitors, during the short-circuit time Inside, the maximum generated heat is as shown in Equation (18), that is, the unshorted capacitors on the short - circuited branch will generate the most serious heat. Severe heat generation in the capacitors will cause a reduction in their service life, or even burn out the capacitors or lead to events such as explosions. Therefore, when a capacitor short - circuit occurs in a certain branch, it is necessary to cut off Figure 2 the entire circuit shown within a short time, so that all capacitor banks stop operating. However, as k increases, the amplitude of will also increase. According to Equation (18), in order to ensure that the generated heat remains unchanged, so when considering the setting of it is considered to make remain unchanged. Let be a constant, which is the fixed value of the generated heat. Then can be set according to Equation (19)

[0166] (19)

[0167] Assume that remains unchanged as a constant value, and n also remains unchanged as a fixed value. Then referring to Equation (13) and Equation (19), is negatively correlated with k, that is, as shown in Equation (20):

[0168] (20)

[0169] Equation (20) shows that is negatively correlated with k. Therefore, the inverse - time setting of can be carried out according to the value of k.

[0170] Combined with the above - mentioned analysis, it can be known that in the Figure 2 circuit, when k sub - capacitors in a certain branch are short - circuited, an unbalanced current will be generated. By sampling and detecting and referring to Equation (4), the value of k can be calculated, and can be set according to Equation (19). The larger k is, the larger is, and referring to Equation (19) and Equation (20), it can be known that in order to keep unchanged, will decrease. Therefore, is set in inverse - time, which decreases with the increase of k and also decreases with the increase of or . Therefore, by setting through Equation (19), it can be ensured that when k capacitors in a certain branch of the Figure 2 circuit are short - circuited, the corresponding circuit breaker is cut off at moment, so that Figure 2Each capacitor stops operating, thereby ensuring that when k is large, the capacitor will not overheat severely and be damaged.

[0171] Figures 1 to 5 Any technical feature in the embodiment corresponding to any one of Figure 6 The corresponding embodiment is also applicable to the embodiment of the present invention. Similar situations will not be elaborated hereinafter.

[0172] The above describes a short - circuit fault protection method for a capacitor bank in an embodiment of the present invention. Next, a device, an electronic device, and a computer - readable storage medium for executing the above - mentioned short - circuit fault protection method for a capacitor bank will be described.

[0173] Referring to Figure 6 An embodiment of the present invention provides a short - circuit fault protection device for a capacitor bank, including

[0174] A first acquisition module 601, configured to acquire the unbalanced current of the neutral line and the phase - bus voltages of each phase of the three - phase bus;

[0175] A first determination module 602, configured to determine the first phase of the unbalanced current and the second phases of the bus voltages;

[0176] A second determination module 603, configured to determine the fault branch and the target bus connected to the fault branch according to the first phase and each second phase;

[0177] A second acquisition module 604, configured to acquire the capacitance value and the total number of capacitors of the capacitors in the fault branch, and the voltage of the target bus;

[0178] A first calculation module 605, configured to calculate the number of faulty capacitors in the fault branch according to the capacitance value, the total number of capacitors, the voltage of the target bus, and the unbalanced current.

[0179] In a specific embodiment, the device further includes:

[0180] A third acquisition module, configured to acquire the fault current of the fault branch, the equivalent resistance of the fault branch, and the heat setting value;

[0181] A second calculation module, configured to calculate the fault operation time according to the amplitude of the fault current, the equivalent resistance, and the heat setting value;

[0182] An update module, configured to update the fault operation time to the relay protection operation time of the relay protection device.

[0183] In a specific embodiment, the second determination module 603 includes:

[0184] A first calculation unit, configured to calculate the phase difference between each second phase and the first phase respectively;

[0185] The first determination unit is configured to determine the phase relationship between each second phase and the first phase according to each phase difference;

[0186] The second determination unit is configured to determine the faulty branch and the target bus connected to the faulty branch according to the phase relationship.

[0187] In a specific embodiment, the second calculation module includes:

[0188] The second calculation unit is configured to calculate the product of the square of the amplitude of the fault current and the equivalent resistance;

[0189] The third calculation unit is configured to calculate the ratio of the heat setting value to the product to obtain the fault operation time.

[0190] An embodiment of the present invention further provides an electronic device, which includes a processor and a memory;

[0191] The memory is used to store program codes and transmit the program codes to the processor;

[0192] The processor is configured to execute the method according to any one of the foregoing embodiments according to the instructions in the program codes.

[0193] An embodiment of the present invention further provides a computer-readable storage medium, which is used to store program codes, and the program codes are used to execute the method according to any one of the foregoing embodiments.

[0194] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the systems, devices, and units described above can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated herein.

[0195] In several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed mutual coupling or direct coupling or communication connection can be through some interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0196] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0197] In addition, in each embodiment of the present invention, each functional unit can be integrated into a processing unit, or each functional unit can exist as an independent physical entity, or two or more functional units can be integrated into a processing unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

[0198] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods in each embodiment of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0199] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of this application and the above-mentioned drawings are used to distinguish similar objects and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments of this application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0200] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. A capacitor bank short circuit fault protection method, characterized in that: The capacitor bank includes a parallel capacitor bank, the parallel capacitor bank includes two capacitor series branches, each of the capacitor series branches includes at least one capacitor, one end of each of the parallel capacitor banks is connected to a three-phase busbar in a one-to-one correspondence, and the other end of each of the parallel capacitor banks is connected to a neutral line, and the method includes: Obtaining the unbalanced current of the neutral line and the bus voltage of each phase of the three-phase bus; Determining a first phase of the unbalanced current and a second phase of each of the bus voltages; Determine, according to the first phase and each of the second phases, a fault branch and a target bus connected to the fault branch; Obtaining the capacitance value and the total number of capacitors in the fault branch and the voltage of the target bus; The number of faulty capacitors in the faulty branch is calculated according to the capacitance value, the total number of capacitors, the voltage of the target bus and the unbalanced current.

2. The method according to claim 1, characterized in that The method further comprises: Obtaining the fault current of the fault branch, the equivalent resistance of the fault branch and the heat setting value; Calculating the fault action time according to the amplitude of the fault current, the equivalent resistance and the heat setting value; The fault action time is updated to the relay protection action time of the relay protection device.

3. The method according to claim 1, characterized in that: The determining, according to the first phase and each of the second phases, a fault branch and a target bus connected to the fault branch comprises: respectively calculating the phase difference between each of the second phases and the first phase; Determining a phase relationship between each of the second phases and the first phase according to each of the phase differences; The faulty branch and a target bus connected to the faulty branch are determined according to the phase relationship.

4. The method according to claim 2, characterized in that: The calculating the fault action time according to the amplitude of the fault current, the equivalent resistance, and the heat setting value comprises: Calculating the product of the square of the amplitude of the fault current and the equivalent resistance; The ratio of the heat set value to the product is calculated to obtain the fault action time.

5. A capacitor bank short circuit fault protection device, characterized in that: The capacitor bank includes a parallel capacitor bank, the parallel capacitor bank includes two capacitor series branches, each of the capacitor series branches includes at least one capacitor, one end of each of the parallel capacitor banks is connected to the three-phase busbars in a one-to-one correspondence, and the other end of each of the parallel capacitor banks is connected to the neutral line, and the device includes: A first acquisition module is used to acquire the unbalanced current of the neutral line and the bus voltage of each phase of the three-phase bus; A first determining module, used to determine a first phase of the unbalanced current and a second phase of each of the bus voltages; A second determination module, configured to determine a faulty branch and a target bus connected to the faulty branch according to the first phase and each of the second phases; A second acquisition module is used to acquire the capacitance value and the total number of capacitors in the fault branch and the voltage of the target bus; The first calculation module is used to calculate the number of faulty capacitors in the faulty branch according to the capacitance value, the total number of capacitors, the voltage of the target bus and the unbalanced current.

6. The device according to claim 5, characterized in that The device also includes: A third acquisition module is used to obtain the fault current of the fault branch, the equivalent resistance of the fault branch and the heat constant; A second calculation module is used to calculate the fault action time according to the amplitude of the fault current, the equivalent resistance and the heat value; The updating module is used to update the fault action time to the relay protection action time of the relay protection device.

7. The device according to claim 5, characterized in that The second determining module comprises: A first calculation unit, used for respectively calculating the phase difference between each of the second phases and the first phase; A first determining unit, configured to determine a phase relationship between each of the second phases and the first phase according to each of the phase differences; The second determining unit is used to determine the faulty branch and a target bus connected to the faulty branch according to the phase relationship.

8. The device according to claim 6, characterized in that The second calculation module includes: A second calculation unit, used for calculating the product of the square of the amplitude of the fault current and the equivalent resistance; The third calculation unit is used to calculate the ratio of the heat set value to the product to obtain the fault action time.

9. An electronic device, characterized in that: The device comprises a processor and a memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the method according to any one of claims 1 to 4 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store program codes, and the program codes are used to execute the method according to any one of claims 1 to 4.

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