Method and device for monitoring unbalanced current at neutral point of parallel capacitor bank

Abstract

The present application relates to a method and device for monitoring the unbalanced current at the neutral point of a parallel capacitor group. The method includes: obtaining a first ratio of the capacitance value of a single element in the parallel capacitor group to the capacitance value of the parallel capacitor group in a fault state; processing the first-level structural parameters of the parallel capacitor group based on the first ratio to determine the range of the number of breakdown elements in the internal series section of the parallel capacitor group; using the range of the number of breakdown elements, obtaining a second ratio based on the second-level structural parameters and the first-level structural parameters, and multiplying the second ratio by the capacitance value of a single element in the parallel capacitor group to determine the range of the single-arm capacitance value of the parallel capacitor group in the fault state; confirming the range of the unbalanced current of the parallel capacitor group based on the range of the single-arm capacitance value of the parallel capacitor group in the fault state, so as to output the unbalanced current attention value and alarm value. The use of this method can timely discover the internal fault of the parallel capacitor group.

Description

Technical Field

[0001] The present application relates to the technical field of electric power equipment, and in particular to a method and device for monitoring unbalanced current at the neutral point of a parallel capacitor group. Background Art

[0002] With the development of power equipment, shunt capacitor banks, as reactive power compensation equipment in power systems, have the functions of reactive power balance and voltage support, and improving the power factor of distribution networks. At present, the connection forms of shunt capacitor banks used in power grids mainly include single star connection and double star connection.

[0003] In traditional technology, neutral point unbalanced current protection is used for high-voltage parallel capacitor banks with double star connection and internal fuses. The effective value of unbalanced current is monitored during operation, and the circuit breaker trips when the protection setting is reached. The protection setting is generally set according to the unbalanced current generated when a certain number of capacitor elements are broken down; when the number of capacitor element breakdowns does not reach the protection setting, the early fault inside the capacitor cannot be found. The damage process of the capacitor is often a process in which the internal elements break down one after another, causing the fault to continue to expand. If the internal state of the capacitor bank is not detected in time, it may cause serious accidents such as bulging or explosion of the capacitor bank.

[0004] However, the current neutral point unbalanced current monitoring method or traditional method of the parallel capacitor group has the problem of being unable to continuously monitor the operating status of the capacitor. Summary of the invention

[0005] Based on this, it is necessary to provide a method and device for monitoring the neutral point unbalanced current of a parallel capacitor that can continuously monitor the operating status of the capacitor in order to solve the above technical problems.

[0006] In a first aspect, the present application provides a method for monitoring unbalanced current at a neutral point of a parallel capacitor bank, the method being applied to a branch circuit including a parallel capacitor bank using a double star connection; the method comprising:

[0007] Obtaining a first ratio of a capacitance value of a single element in the parallel capacitor bank to a capacitance value of the parallel capacitor bank in a fault state;

[0008] Processing the first level structural parameters of the shunt capacitor bank based on the first ratio to determine the range of the number of breakdown components in the series section inside the shunt capacitor bank;

[0009] A second ratio is obtained based on the second-level structural parameter and the first-level structural parameter using the range of the number of breakdown components, and the product of the second ratio and the capacitance value of a single component in the parallel capacitor group is determined as the range of the single-arm capacitance value of the parallel capacitor group in the fault state; wherein the structural level of the first-level structural parameter is greater than that of the second-level structural parameter;

[0010] According to the range of the single-arm capacitance value of the parallel capacitor bank under the fault state, the range of the unbalanced current of the parallel capacitor bank is confirmed to output the unbalanced current attention value and the unbalanced current alarm value.

[0011] In one of the embodiments, the capacitance value of the parallel capacitor bank in the fault state is a preset percentage of the rated capacitance of the parallel capacitor bank.

[0012] In one embodiment, the predetermined percentage is 95%.

[0013] In one embodiment, the first-level structural parameters are unit structural parameters; the unit structural parameters include the number of series segments of the parallel capacitor bank and the number of parallel elements in each series segment of the parallel capacitor bank; the second-level structural parameters are wiring structural parameters; the wiring structural parameters include the number of series segments of each phase single arm of the parallel capacitor bank and the number of parallel capacitors in each series segment of the single arm;

[0014] The method also includes the step of obtaining wiring structure parameters according to the equivalent circuit of the parallel capacitor group.

[0015] In one embodiment, the second ratio is obtained based on the following formula:

[0016]

[0017] Among them, i is the number of breakdown elements in the series section inside the parallel capacitor group; m is the number of parallel elements in each series section in the parallel capacitor group; n is the number of series sections of the parallel capacitor group; M is the number of parallel capacitors in each series section of a single arm; N is the number of series sections of each phase of a single arm of the parallel capacitor group; R2 is the second ratio.

[0018] In one embodiment, the branch further includes a series reactor; the range of the unbalanced current of the parallel capacitor bank is obtained based on the following formula:

[0019]

[0020] Wherein, C4 is the single-arm capacitance value of the parallel capacitor bank in the fault state; C3 is the single-arm capacitance value of the parallel capacitor bank in the normal state; U S is the system voltage; K is the reactance rate of the series reactor; I0 is the unbalanced current of the parallel capacitor group.

[0021] In one embodiment, the unbalanced current notice value is the minimum value in the range of the unbalanced current; and the unbalanced current alarm value is the maximum value in the range of the unbalanced current.

[0022] In a second aspect, the present application further provides a device for monitoring neutral point unbalanced current of a parallel capacitor bank, the device comprising:

[0023] A first ratio acquisition module, used to acquire a first ratio of a capacitance value of a single element in the parallel capacitor bank to a capacitance value of the parallel capacitor bank in a fault state;

[0024] A breakdown component number range determination module, used to process the first-level structural parameters of the parallel capacitor bank based on the first ratio to determine the range of the number of breakdown components in the series section inside the parallel capacitor bank;

[0025] A single-arm capacitance value range determination module is used to obtain a second ratio based on the second-level structural parameter and the first-level structural parameter using the range of the number of breakdown components, and determine the product of the second ratio and the capacitance value of a single component in the parallel capacitor group as the range of the single-arm capacitance value of the parallel capacitor group in the fault state; wherein the structural level of the first-level structural parameter is greater than the second-level structural parameter;

[0026] The unbalanced current warning value output module is used to confirm the range of the unbalanced current of the parallel capacitor group according to the range of the single-arm capacitance value of the parallel capacitor group in the fault state, so as to output the unbalanced current attention value and the unbalanced current alarm value.

[0027] In a third aspect, the present application also provides a parallel capacitor group neutral point unbalanced current monitor, including a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0028] In a fourth aspect, the present application also provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the above method when the computer program is executed by a processor.

[0029] In a fifth aspect, the present application further provides a computer program product, wherein the computer program product comprises a computer program, and when the computer program is executed by a processor, the steps of the above method are implemented.

[0030] The above-mentioned method, device, parallel capacitor bank neutral point unbalanced current monitoring instrument, storage medium and computer program product are based on

[0031] The output unbalanced current attention value and unbalanced current alarm value can realize fault warning before the neutral point unbalanced current rises to the protection action tripping during the neutral point unbalanced current monitoring process of the double star-connected parallel capacitor group, and detect the internal fault of the parallel capacitor group in advance, which is convenient for operation and maintenance personnel to shut down the power for inspection in time and improve the reliability of equipment operation and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a primary wiring diagram of a parallel capacitor bank in one embodiment;

[0033] Figure 2 1 is a flow chart of a method for monitoring unbalanced current at a neutral point of a parallel capacitor bank in one embodiment;

[0034] Figure 3 is a structural block diagram of a device for monitoring neutral point unbalanced current of a parallel capacitor bank in one embodiment;

[0035] Figure 4 FIG. 1 is an internal structure diagram of a neutral point unbalanced current monitor for a parallel capacitor bank in one embodiment. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0037] It should be noted that if Figure 1 As shown, in the present application, the double star neutral point unbalanced current protection plus phase voltage differential protection, the primary wiring branch includes a circuit breaker, a series reactor, a parallel capacitor bank and a parallel capacitor bank neutral point unbalanced current transformer, etc. The internal structure of the double star-connected parallel capacitor bank is an internal fuse structure. The parallel capacitor bank is composed of multiple capacitor elements connected in parallel and in series. When several capacitor elements in the parallel capacitor bank fail, the internal fuse will cut off the several failed capacitor elements. At this time, the capacitance value of the parallel capacitor bank decreases. The change in the capacitance value of the parallel capacitor bank causes the balance between the bridge arms to change, thereby generating a neutral point unbalanced current.

[0038] Specifically, the number of series sections of the parallel capacitor bank is n; the number of parallel elements in each series section of the parallel capacitor bank is m; the capacitance value of a single element in the parallel capacitor bank is C x The capacitor element has internal fuse protection and internal discharge resistance, and the impedance of the internal discharge resistance is much greater than the capacitive reactance of the corresponding parallel capacitor, so the impedance of the internal discharge resistance can be ignored. The parallel capacitor group has a series reactor, and the reactance rate of the series reactor is K.

[0039] Furthermore, the connection form of the parallel capacitor bank is that the number of parallel capacitors in each series section of a single arm is M, and the number of series sections of each phase of the single arm of the parallel capacitor bank is N; the capacitance value of the parallel capacitor bank under normal conditions is C1; then the following formula is obtained:

[0040]

[0041] When a fault occurs inside the parallel capacitor bank, the internal fuse of the faulty component operates to disconnect the corresponding faulty component. At this time, the number of breakdown components in the series section inside the parallel capacitor bank is i; the capacitance value of the parallel capacitor bank under the fault state is C2, and the following formula is obtained:

[0042]

[0043] The capacitance change per unit value of the parallel capacitor group is α1, then the following formula is obtained:

[0044]

[0045] The failure rate of the parallel capacitor group is β, then the following formula is obtained:

[0046]

[0047] The single-arm capacitance value of the parallel capacitor bank under normal conditions is C3, and the following formula is obtained:

[0048]

[0049] When the fault occurs in a single arm of the capacitor bank, the capacitance of the single arm of the parallel capacitor bank under the fault state is C4, and the capacitance of the single arm series section of the parallel capacitor bank under the fault state is C y , then we have the following formula:

[0050]

[0051]

[0052]

[0053] The per-unit capacitance change of a single-arm capacitor bank is α2, and the following formula is obtained:

[0054]

[0055] Using Kirchhoff's current law, the current flowing into the neutral point is equal to the current flowing out of the neutral point, so we have the following formula:

[0056]

[0057] Among them, the capacitance value of one arm (i.e. A1) of the parallel capacitor group under fault condition is C4 (i.e. the capacitance value of the single arm of the parallel capacitor group under fault condition); the capacitance values ​​of the remaining five arms (i.e. A2, B1, B2, C1 and C2) are all C3 (i.e. the capacitance value of the single arm of the parallel capacitor group under normal condition); according to U A +U B +U C =0, then we have the following formula:

[0058]

[0059] The unbalanced current of the parallel capacitor bank is I0 = I A1 +I B1 +I C1 ,Right now:

[0060] I0=(U A -U0)jωC3+(U B -U0)jωC3+(U C -U0)jωC3=-3ωU0C3

[0061]

[0062] Where C3 is a known value, U A is the terminal voltage of the parallel capacitor group. Due to the existence of the series reactor, the following formula is obtained:

[0063]

[0064] Among them, U S is the system voltage; during the actual operation of the system, C3, I0 and U S are all known values, then the formula as well as The following formula can be obtained:

[0065]

[0066] Based on the following formula:

[0067]

[0068] The following formula can be obtained:

[0069]

[0070] At present, the neutral point unbalanced current protection is adopted for the parallel capacitor bank with internal fuse structure. The effective value of unbalanced current is monitored during operation, and the circuit breaker is tripped when the protection setting value is reached. The protection setting value is generally set according to the unbalanced current generated when a certain number of capacitor elements are broken down; when the number of capacitor elements broken down does not reach the protection setting value, the early fault inside the capacitor cannot be found.

[0071] It is known that the starting setting of the unbalanced current protection of the neutral point CT of the parallel capacitor bank is I,U S Taking the bus rated voltage, according to equations (1) and (2), we have the following equation:

[0072]

[0073] Wherein, k is the number of breakdown elements in the series section inside the parallel capacitor bank when the unbalanced current protection is activated.

[0074] In one embodiment, Figure 2 As shown, a method for monitoring the unbalanced current at the neutral point of a parallel capacitor bank is provided, and the method is applied to a branch circuit including a parallel capacitor bank using a double star connection; the method comprises:

[0075] Step 210, obtaining a first ratio of a capacitance value of a single element in the parallel capacitor bank to a capacitance value of the parallel capacitor bank in a fault state;

[0076] Specifically, the capacitance of a single element in a parallel capacitor bank is C x ; The capacitance of the parallel capacitor bank in the fault state is C2; The first ratio is R1; In some examples,

[0077] In one of the embodiments, the capacitance value of the parallel capacitor bank in the fault state is a preset percentage of the rated capacitance of the parallel capacitor bank.

[0078] Specifically, the rated capacitance of the parallel capacitor bank is C n ; With a preset percentage of C n As a reference value for obtaining the unbalanced current attention value and the unbalanced current alarm value, that is, the capacitance value of the parallel capacitor group in the fault state is the rated capacitance of the parallel capacitor group reduced by the remaining preset percentage, and the unbalanced current generated at this time is used as the reference value of the unbalanced current attention value and the unbalanced current alarm value; in some examples, the remaining preset percentage is 5%.

[0079] In one embodiment, the predetermined percentage is 95%.

[0080] Specifically, according to the requirements of DL / T 840 (Technical Conditions for the Use of High-voltage Shunt Capacitors), the capacitance value of the frame-type shunt capacitor set should meet the following requirements: 1) The capacitance value deviation should not exceed the rated range of -5% to +5%; 2) The capacitance value should not be less than 95% of the factory value. When a fault occurs inside the shunt capacitor group, causing the capacitance value to drop by more than 5% of the rated value (i.e., β = 5%), the corresponding faulty capacitor should be replaced.

[0081] In some examples, C2 = 95% C n , at 95%C n As a reference value for obtaining the unbalanced current warning value and the unbalanced current alarm value, at this time,

[0082] Step 220, processing the first level structural parameters of the parallel capacitor bank based on the first ratio, and determining the range of the number of breakdown components in the series section inside the parallel capacitor bank;

[0083] Specifically, the first-level structural parameters are unit structural parameters; the unit structural parameters include the number of series segments n of the parallel capacitor group and the number of parallel elements m of each series segment in the parallel capacitor group; the number of breakdown elements in the series segment inside the parallel capacitor group ranges from a to b;

[0084] In some examples, the range a to b of the number of breakdown elements in the series section within the parallel capacitor bank is determined based on the following formula:

[0085]

[0086] Where n is the number of series sections of the parallel capacitor bank; m is the number of parallel elements in each series section of the parallel capacitor bank; i = (a ~ b) < k;

[0087] In some examples, when the value is a decimal, b can be rounded up by adding one, a=b-1;

[0088] Step 230, using the range of the number of breakdown components, obtaining a second ratio based on the second-level structural parameters and the first-level structural parameters, and multiplying the second ratio by the capacitance value of a single component in the parallel capacitor group to determine the range of the single-arm capacitance value of the parallel capacitor group in the fault state; wherein the structural level of the first-level structural parameters is greater than that of the second-level structural parameters;

[0089] In one embodiment, the first-level structural parameters are unit structural parameters; the unit structural parameters include the number of series segments of the parallel capacitor bank and the number of parallel elements in each series segment of the parallel capacitor bank; the second-level structural parameters are wiring structural parameters; the wiring structural parameters include the number of series segments of each phase single arm of the parallel capacitor bank and the number of parallel capacitors in each series segment of the single arm;

[0090] The method also includes the step of obtaining wiring structure parameters according to the equivalent circuit of the parallel capacitor group.

[0091] In one embodiment, the second ratio is obtained based on the following formula:

[0092]

[0093] Among them, i is the number of breakdown elements in the series section inside the parallel capacitor group; m is the number of parallel elements in each series section in the parallel capacitor group; n is the number of series sections of the parallel capacitor group; M is the number of parallel capacitors in each series section of a single arm; N is the number of series sections of each phase of a single arm of the parallel capacitor group; R2 is the second ratio.

[0094] Step 240, confirming the range of the unbalanced current of the parallel capacitor bank according to the range of the single-arm capacitance value of the parallel capacitor bank in the fault state, so as to output the unbalanced current attention value and the unbalanced current alarm value.

[0095] In one embodiment, the unbalanced current notice value is the minimum value in the range of the unbalanced current; and the unbalanced current alarm value is the maximum value in the range of the unbalanced current.

[0096] Specifically, the unbalanced current of the output unbalanced current I0 has an unbalanced current range of A to B; wherein, when I0=A, it is an unbalanced current attention value, and when I0=B, it is an unbalanced current alarm value.

[0097] In some examples, the measurement and control transmits the sampled data of the unbalanced current transformer at the neutral point of the parallel capacitor group to the background, obtains the trend graph of the unbalanced current I0 changing with time, and compares the unbalanced current I0 with the unbalanced current attention value A and the unbalanced current alarm value B.

[0098] In one embodiment, the branch further includes a series reactor; the range of the unbalanced current of the parallel capacitor bank is obtained based on the following formula:

[0099]

[0100] Wherein, C4 is the single-arm capacitance value of the parallel capacitor bank in the fault state; C3 is the single-arm capacitance value of the parallel capacitor bank in the normal state; U S is the system voltage; K is the reactance rate of the series reactor; I0 is the unbalanced current of the parallel capacitor group.

[0101] When the unbalanced current online monitoring alarm occurs, a fault occurs inside the parallel capacitor bank, but the number of breakdown components i in the series section of the parallel capacitor bank has not yet reached the k value of the unbalanced current protection action. This method can achieve the purpose of discovering faults before the protection action trips, so that the operation and maintenance personnel can grasp the operating status of the capacitor bank in time, handle the faulty capacitor unit in time, improve the equipment operation and maintenance level, and improve the reliability of power grid operation.

[0102] In some examples, the monitoring interface displays in real time the value of the unbalanced current I0 of the parallel capacitor group, the number of breakdown elements i in the series segment of the parallel capacitor group corresponding to the I0 value, and the failure rate β of the parallel capacitor group. When i>b, the i value can be used to give an alarm by flashing light; when β>5%, the β value can be used to give an alarm by flashing light. Among them, the number of breakdown elements i in the series segment of the parallel capacitor group and the failure rate β of the parallel capacitor group are based on formula (1) and formula (2), and the known number of series segments n of the parallel capacitor group, the number of parallel elements m in each series segment of the parallel capacitor group, the number of series segments n of the parallel capacitor group, the number of parallel capacitors M in each series segment of a single arm, the number of series segments N of each phase of the single arm of the parallel capacitor group, and the capacitance value C of a single element in the parallel capacitor group are processed. x 、System voltage U S And the unbalanced current I0 of the parallel capacitor group measured in real time is obtained.

[0103] In some examples, the unbalanced current generated when the internal components of the parallel capacitor group break down is I2, and the unbalanced current before the change is I1, and the mutation amount ΔI=I2-I1. Taking the unbalanced current I0 (i=1) of the parallel capacitor group when i=1 as a reference, when ΔI=I0 (i=1 is the preset alarm value), the online monitoring background will give an alarm. When I0=A, a power outage inspection should be arranged as soon as possible, and the faulty capacitor should be replaced or the bridge arm capacitance should be readjusted; when ΔI exceeds the preset alarm value, attention should be paid. When I0 is close to the attention value, ΔI exceeds the preset alarm value but the I0 value does not increase but decreases. It is possible that different arms of the parallel capacitor group are broken down. The operation and maintenance personnel should shut down the power for inspection as soon as possible; when I0 does not reach the attention value but ΔI continuously alarms, continuous breakdown may occur inside the parallel capacitor group. At this time, the power should also be shut down for inspection as soon as possible.

[0104] In some examples, the method is applied to a set of capacitor sets, model TBB35-60000 / 500BLW+ACW, in which the reactance K of a set of series reactors is 12%, and the model of the parallel capacitor group is BAM12 / 2-500-1W. The parallel capacitor group is all single-tube outlet, and the other stage is connected to the capacitor housing and led out. The internal component connection form of the parallel capacitor group is 18 parallel and 4 series (that is, the number of parallel elements in each series segment of the parallel capacitor group is m=18, and the number of series segments of the parallel capacitor group is n=4); the parallel capacitor group has internal fuse protection and internal discharge resistance. The capacitor device is wired in double star connection, equipped with neutral point unbalanced current protection plus phase voltage differential protection. The parallel capacitor group has 40 capacitors per phase, (5+5) parallel and 4 series (that is, the number of parallel capacitors in each series section of a single arm M=5; the number of series sections of each arm of the parallel capacitor group per phase N=4) double branch arrangement, the capacitor is installed horizontally, and a total of 40 capacitors per phase are arranged on 4 insulating platforms, and there are 10 capacitors on each insulating platform, which are electrically connected in 5 parallel and 2 series. The double star neutral point unbalanced current protection setting is 1A, k=(5~6), C1=44μF, and C is obtained through C1 x =9.778μF; C3 = 55μF, according to 95% C1, i = (3-4), A = 0.476A, B = 0.669A, then the following formula is obtained:

[0105]

[0106]

[0107] In this embodiment, the neutral point unbalanced current of the double star-connected parallel capacitor group is monitored online in real time, and the neutral point unbalanced current value is analyzed to achieve the purpose of monitoring the operating status of the capacitor group. In this embodiment, fault warning can be achieved before the unbalanced current rises to the point where the protection action trips, and internal faults of the capacitor can be discovered in advance, which facilitates the operation and maintenance personnel to shut down the power in time for inspection, thereby improving the reliability of equipment operation and maintenance.

[0108] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0109] Based on the same inventive concept, the embodiment of the present application also provides a parallel capacitor bank neutral point unbalanced current monitoring device for implementing the above-mentioned parallel capacitor bank neutral point unbalanced current monitoring method. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above-mentioned method, so the specific limitations in the embodiments of one or more parallel capacitor bank neutral point unbalanced current monitoring devices provided below can refer to the limitations of the parallel capacitor bank neutral point unbalanced current monitoring method above, and will not be repeated here.

[0110] In one embodiment, Figure 3 As shown, a device for monitoring the neutral point unbalanced current of a parallel capacitor bank is provided, the device comprising:

[0111] A first ratio acquisition module 310, used to acquire a first ratio of a capacitance value of a single element in a parallel capacitor bank to a capacitance value of the parallel capacitor bank in a fault state;

[0112] A breakdown component number range determination module 320, configured to process the first level structural parameters of the parallel capacitor bank based on the first ratio to determine the range of the number of breakdown components of the series section inside the parallel capacitor bank;

[0113] The single-arm capacitance value range determination module 330 is used to obtain a second ratio based on the second-level structural parameter and the first-level structural parameter using the range of the number of breakdown components, and determine the range of the single-arm capacitance value of the parallel capacitor group under the fault state by multiplying the second ratio by the capacitance value of a single component in the parallel capacitor group; wherein the structural level of the first-level structural parameter is greater than that of the second-level structural parameter;

[0114] The unbalanced current warning value output module 340 is used to determine the range of the unbalanced current of the parallel capacitor group according to the range of the single-arm capacitance value of the parallel capacitor group in the fault state, so as to output the unbalanced current attention value and the unbalanced current alarm value.

[0115] In one of the embodiments, a wiring structure parameter acquisition module is further included, which is used to acquire the wiring structure parameters according to the equivalent circuit of the parallel capacitor group.

[0116] In one embodiment, the single-arm capacitance value range determination module obtains the second ratio based on the following formula:

[0117]

[0118] Wherein, i is the number of breakdown elements in the series segment inside the parallel capacitor bank; m is the number of parallel elements in each series segment in the parallel capacitor bank; n is the number of series segments of the parallel capacitor bank; M1 is the number of parallel capacitors in each series segment of a single arm; N is the number of series segments of each phase single arm of the parallel capacitor bank; R2 is the second ratio;

[0119] In one embodiment, the unbalanced current warning value output module obtains the range of the unbalanced current of the parallel capacitor bank based on the following formula:

[0120]

[0121] Wherein, C4 is the single-arm capacitance value of the parallel capacitor bank in the fault state; C3 is the single-arm capacitance value of the parallel capacitor bank in the normal state; U S is the system voltage; K is the reactance rate of the series reactor; I0 is the unbalanced current of the parallel capacitor group.

[0122] Each module in the above-mentioned shunt capacitor bank neutral point unbalanced current monitoring device can be implemented in whole or in part by software, hardware and a combination thereof. Each of the above-mentioned modules can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to each of the above modules.

[0123] In one embodiment, a parallel capacitor bank neutral point unbalanced current monitor is provided, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0124] In one embodiment, a parallel capacitor bank neutral point unbalanced current monitor is provided. The parallel capacitor bank neutral point unbalanced current monitor can be a terminal, and its internal structure diagram can be as shown in FIG. Figure 4As shown. The neutral point unbalanced current monitor of the parallel capacitor group includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the neutral point unbalanced current monitor of the parallel capacitor group is used to provide computing and control capabilities. The memory of the neutral point unbalanced current monitor of the parallel capacitor group includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the neutral point unbalanced current monitor of the parallel capacitor group is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be implemented through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. When the neutral point unbalanced current monitor of the parallel capacitor group is executed by the processor, a method for monitoring the neutral point unbalanced current of the parallel capacitor group is implemented. The display screen of the parallel capacitor group neutral point unbalanced current monitor can be a liquid crystal display screen or an electronic ink display screen, and the input device of the parallel capacitor group neutral point unbalanced current monitor can be a touch layer covered on the display screen, or a button, trackball or touchpad set on the shell of the parallel capacitor group neutral point unbalanced current monitor, or an external keyboard, touchpad or mouse, etc.

[0125] Those skilled in the art will understand that Figure 4 The structure shown in the figure is only a block diagram of a part of the structure related to the scheme of the present application, and does not constitute a limitation on the neutral point unbalanced current monitor of the parallel capacitor group to which the scheme of the present application is applied. The specific neutral point unbalanced current monitor of the parallel capacitor group may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0126] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above method are implemented.

[0127] In one embodiment, a computer program product is provided, wherein the computer program product comprises a computer program, and when the computer program is executed by a processor, the steps of the above method are implemented.

[0128] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0129] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for monitoring unbalanced current at the neutral point of a parallel capacitor bank, characterized in that: The method is applied to a branch circuit including a parallel capacitor bank using a double star connection; the method comprises: Obtaining a first ratio of a capacitance value of a single element in the parallel capacitor bank to a capacitance value of the parallel capacitor bank in a fault state; Processing the first-level structural parameters of the parallel capacitor bank based on the first ratio to determine the range of the number of breakdown elements in the series section inside the parallel capacitor bank; Using the range of the number of breakdown elements, a second ratio is obtained based on the second-level structural parameter and the first-level structural parameter, and the product of the second ratio and the capacitance value of a single element in the parallel capacitor group is determined as the range of the single-arm capacitance value of the parallel capacitor group under the fault state; wherein the structural level of the first-level structural parameter is greater than that of the second-level structural parameter; According to the range of the single-arm capacitance value of the parallel capacitor group under the fault state, the range of the unbalanced current of the parallel capacitor group is confirmed to output the unbalanced current attention value and the unbalanced current alarm value; the first-level structural parameter is a unit structural parameter; the unit structural parameter includes the number of series sections of the parallel capacitor group and the number of parallel elements of each series section in the parallel capacitor group; the second-level structural parameter is a wiring structural parameter; the wiring structural parameter includes the number of series sections of each phase single arm of the parallel capacitor group and the number of parallel capacitors in each series section of the single arm; It also includes the steps of: acquiring the wiring structure parameters according to the equivalent circuit of the parallel capacitor group; The second ratio is obtained based on the following formula: Wherein, i is the number of breakdown elements in the series segment inside the parallel capacitor group; m is the number of parallel elements in each series segment in the parallel capacitor group; n is the number of series segments of the parallel capacitor group; M is the number of parallel capacitors in each series segment of the single arm; N is the number of series segments of each phase single arm of the parallel capacitor group; R2 is the second ratio; The branch circuit also includes a series reactor; The range of the unbalanced current of the parallel capacitor bank is obtained based on the following formula: Wherein, C4 is the single-arm capacitance value of the parallel capacitor bank in the fault state; C3 is the single-arm capacitance value of the parallel capacitor bank in the normal state; U S is the system voltage; K is the reactance rate of the series reactor; I0 is the unbalanced current of the parallel capacitor group.

2. The method for monitoring the neutral point unbalanced current of a parallel capacitor bank according to claim 1, characterized in that: The capacitance value of the parallel capacitor group in the fault state is a preset percentage of the rated capacitance of the parallel capacitor group.

3. The method for monitoring the neutral point unbalanced current of a parallel capacitor bank according to claim 2, characterized in that: The preset percentage is 95%.

4. The method for monitoring the neutral point unbalanced current of a parallel capacitor bank according to claim 1, characterized in that: The unbalanced current attention value is a minimum value in the range of the unbalanced current.

5. The method for monitoring the neutral point unbalanced current of a parallel capacitor bank according to claim 1, characterized in that: The unbalanced current alarm value is a maximum value in the range of the unbalanced current.

6. A device for monitoring neutral point unbalanced current of a parallel capacitor bank, characterized in that: Applicable to a branch circuit containing a parallel capacitor bank adopting double star connection; the device comprises: A first ratio acquisition module, used to acquire a first ratio of a capacitance value of a single element in the parallel capacitor bank to a capacitance value of the parallel capacitor bank in a fault state; A breakdown element number range determination module, configured to process the first-level structural parameters of the parallel capacitor group based on the first ratio to determine the range of the number of breakdown elements in the series segment inside the parallel capacitor group; the first-level structural parameters are unit structural parameters; the unit structural parameters include the number of series segments of the parallel capacitor group and the number of parallel elements in each series segment of the parallel capacitor group; A single-arm capacitance value range determination module is used to obtain a second ratio based on the second-level structural parameter and the first-level structural parameter using the range of the number of breakdown elements, and determine the product of the second ratio and the capacitance value of a single element in the parallel capacitor group as the range of the single-arm capacitance value of the parallel capacitor group under the fault state; wherein the structural level of the first-level structural parameter is greater than the second-level structural parameter; the second-level structural parameter is a wiring structure parameter; the wiring structure parameter includes the number of series sections of each phase of the single arm of the parallel capacitor group and the number of parallel capacitors in each series section of the single arm; an unbalanced current warning value output module, used to confirm the range of the unbalanced current of the parallel capacitor group according to the range of the single-arm capacitance value of the parallel capacitor group in the fault state, so as to output an unbalanced current attention value and an unbalanced current alarm value; A wiring structure parameter acquisition module, used to acquire the wiring structure parameters according to the equivalent circuit of the parallel capacitor group; The single-arm capacitance value range determination module is further used to obtain a second ratio based on the following formula: Wherein, i is the number of breakdown elements in the series segment inside the parallel capacitor group; m is the number of parallel elements in each series segment in the parallel capacitor group; n is the number of series segments of the parallel capacitor group; M is the number of parallel capacitors in each series segment of the single arm; N is the number of series segments of each phase single arm of the parallel capacitor group; R2 is the second ratio; The unbalanced current warning value output module is further used to obtain the range of the unbalanced current of the parallel capacitor group based on the following formula: Wherein, the branch also includes a series reactor; C4 is the single-arm capacitance value of the parallel capacitor group in the fault state; C3 is the single-arm capacitance value of the parallel capacitor group in the normal state; U S is the system voltage; K is the reactance rate of the series reactor; I0 is the unbalanced current of the parallel capacitor group.

7. A parallel capacitor bank neutral point unbalanced current monitor, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

9. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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