Transformer protection longitudinal difference current correction method and device based on zero sequence difference current

Abstract

The invention discloses a transformer protection longitudinal difference and differential current correction method based on zero sequence differential current, which comprises the following steps of: acquiring current of each side of a transformer, and calculating an instantaneous value of the adjustment current of each side according to equipment parameters of the transformer; calculating a three-phase difference current instantaneous value according to the adjustment current instantaneous value of each side, and calculating the maximum absolute value of the three-phase difference current instantaneous value; according to the three-phase difference current instantaneous value and the maximum absolute value of the three-phase difference current instantaneous value, a zero-sequence difference current reference value is calculated; and calculating a three-phase correction differential current instantaneous value according to the zero-sequence differential current reference value. According to the method provided by the invention, when the longitudinal differential current of the transformer is calculated, the adjustment current without reducing the zero sequence is used on each side of the transformer, the influence of the zero sequence differential current on a non-fault phase is eliminated while the fault differential current is increased, and the sensitivity of longitudinal differential protection can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of relay protection of electric power systems, and in particular to a method and device for correcting longitudinal differential current of transformer protection based on zero-sequence differential current. Background Art

[0002] The rated current and the number of hours on each side of the transformer are different, so the amplitude and phase of the current on each side need to be corrected when calculating the adjustment current on each side. When the transformer has a delta connection, the current transformer is usually installed outside the delta winding ring. Since there is no zero-sequence current loop, the current transformer cannot collect zero-sequence current. When the neutral point on the star winding side of the transformer is grounded, the current transformer on the star winding side can collect zero-sequence current. Therefore, when calculating the adjustment current, the star winding side needs to eliminate the zero sequence, otherwise the calculated phase differential current will have a zero-sequence differential current component.

[0003] When a single-phase or two-phase grounding fault occurs in the transformer, the zero sequence subtracted when calculating the adjustment current on the star winding side is not the zero-sequence current component that actually causes the zero-sequence differential current. Therefore, this method of calculating the adjustment current will cause the effective value of the longitudinal differential current to become smaller, reducing the sensitivity of the longitudinal differential protection. In order to improve the sensitivity of the longitudinal differential protection, the zero sequence can be calculated without subtracting the adjustment current on the star winding side. However, this method will have a zero-sequence differential current component when there is a grounding fault outside the zone, which may cause the protection to malfunction. In order to improve the sensitivity of the longitudinal differential protection and eliminate the influence of the zero-sequence differential current, a transformer protection longitudinal differential current correction method based on the zero-sequence differential current is proposed. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a transformer protection longitudinal differential current correction method and device based on zero-sequence differential current, which does not subtract zero sequence when calculating the adjustment current on the star winding side, thereby improving the sensitivity of the longitudinal differential protection and eliminating the influence of the zero-sequence differential current.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] According to a first aspect of the present invention, a transformer protection longitudinal differential current correction method based on zero-sequence differential current is proposed, which is characterized by comprising the following steps:

[0007] Collect the current on each side of the transformer, and calculate the instantaneous value of the adjustment current on each side according to the transformer equipment parameters, wherein the zero-sequence current is not subtracted when calculating the instantaneous value of the adjustment current on the star side of the transformer, and the adjustment current is converted to the star side when calculating the instantaneous value of the adjustment current on the angle side of the transformer;

[0008] Calculating the instantaneous value of the three-phase differential current according to the instantaneous value of the adjusted current on each side, and calculating the maximum absolute value of the instantaneous value of the three-phase differential current;

[0009] Calculate the zero-sequence differential current reference value according to the instantaneous values of the three-phase differential currents and the maximum absolute value of the instantaneous values of the three-phase differential currents;

[0010] Calculate the instantaneous values of the three-phase corrected differential currents according to the zero-sequence differential current reference value.

[0011] According to some embodiments, the specific calculation of the maximum absolute value of the instantaneous values of the three-phase differential currents is as follows:

[0012] When and the duration reaches t1, if then When and the duration reaches t2, Otherwise Remain unchanged;

[0013] Wherein, is the instantaneous value of the differential current between phases, Take a, b, c, which respectively represent phase a, phase b, and phase c; id_set is the differential current judgment threshold value, is the maximum absolute value of the instantaneous value of the differential current between phases, t1 is the first delay setting value, and t2 is the second delay setting value.

[0014] According to some embodiments, the value range of the differential current judgment threshold value id_set is 0.01 - 0.25Ie, where Ie is the rated current; the value range of the first delay setting value t1 is less than 5 ms, and the value range of the second delay setting value t2 is not less than 10 ms.

[0015] According to some embodiments, it further includes calculating the minimum value id min of the maximum absolute value of the instantaneous values of the three-phase differential currents, specifically:

[0016] id min = min{ida max , idb max , idc max}.

[0017] According to some embodiments, the calculation of the zero-sequence differential current reference value is specifically:

[0018] Calculate the zero-sequence differential current 3id0 = ida + idb + idc;

[0019] When |3id0| > id0_set and the duration reaches t3, set the zero-sequence flag of the differential current; when |3id0| < id0_set and the duration reaches t4, clear the zero-sequence flag of the differential current; otherwise, the zero-sequence flag of the differential current remains unchanged; wherein, id 0_set is the zero-sequence differential current judgment threshold value, t3 is the third delay setting value, and t4 is the fourth delay setting value;

[0020] When the differential current has a zero sequence flag set, if id min =ida max , then the zero-sequence differential current reference value id0_ref takes the phase differential current, that is, id0_ref = id a ; If id min =idb max , then the zero-sequence differential current reference value id0_ref takes the b-phase differential current, that is, id0_ref = id b ; If id min =idc max , then the zero-sequence differential current reference value id0_ref takes the c-phase differential current, that is, id0_ref = id c ;

[0021] When the zero-sequence flag of the differential current is not in the set state, the zero-sequence differential current reference value id0_ref is set to 0, that is, id0_ref=0.

[0022] According to some embodiments, the zero-sequence differential current judgment threshold value id0_set has a value range of 0.01 to 0.25Ie, where Ie is the rated current; the third delay constant t3 has a value range of less than 5ms, and the fourth delay constant t4 has a value range of not less than 10ms.

[0023] According to some embodiments, the instantaneous value of the three-phase corrected differential current is calculated according to the zero-sequence differential current reference value, specifically:

[0024]

[0025] in, for Phase correction differential current instantaneous value, Take a, b, and c to represent phase a, phase b, and phase c respectively.

[0026] According to a second aspect of the present invention, a transformer protection longitudinal differential current correction device based on zero-sequence differential current is proposed, comprising:

[0027] A data acquisition unit, used to collect currents on each side of the transformer;

[0028] A calculation unit is used to calculate the instantaneous value of the adjusted current on each side according to the transformer equipment parameters, wherein the zero-sequence current is not subtracted when calculating the instantaneous value of the adjusted current on the star side of the transformer, and the instantaneous value of the adjusted current on the corner side of the transformer is converted to the star side; the instantaneous value of the three-phase differential current is calculated according to the instantaneous value of the adjusted current on each side, and the maximum absolute value of the three-phase differential current instantaneous value is calculated; the zero-sequence differential current reference value is calculated according to the instantaneous value of the three-phase differential current and the maximum absolute value of the three-phase differential current instantaneous value; and the instantaneous value of the three-phase corrected differential current is calculated according to the zero-sequence differential current reference value.

[0029] According to a third aspect of the present invention, an electronic device is proposed, comprising: a processor; and a memory storing computer instructions, wherein when the computer instructions are executed by the processor, the processor executes the transformer protection longitudinal differential current correction method based on zero-sequence differential current as described above.

[0030] According to a fourth aspect of the present invention, a non-transitory computer storage medium is proposed, storing a computer program. When the computer program is executed by multiple processors, the processors execute the transformer protection longitudinal differential current correction method based on zero-sequence differential current as described above.

[0031] The beneficial effects of the present invention are as follows: by adopting the technical solution of the present invention, it is possible to use an adjustment current without reducing the zero sequence on each side of the transformer when calculating the longitudinal differential current of the transformer, thereby increasing the differential current of the fault phase while eliminating the influence of the zero sequence differential current on the non-fault phase, thereby greatly improving the sensitivity of the longitudinal differential protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic flow chart of a transformer protection longitudinal differential current correction method based on zero-sequence differential current provided in an exemplary embodiment of the present invention;

[0033] Figure 2 A waveform diagram of currents on each side of a transformer collected when a phase A ground fault occurs in a transformer protection zone provided by an exemplary embodiment of the present invention;

[0034] Figure 3 The instantaneous value of the three-phase differential current and the zero-sequence differential current waveform in the exemplary embodiment of the present invention;

[0035] Figure 4 A schematic diagram of instantaneous values ​​of three-phase corrected differential currents calculated in an exemplary embodiment of the present invention;

[0036] Figure 5 A schematic diagram of the structure of a transformer protection longitudinal differential current correction device based on zero-sequence differential current provided in an exemplary embodiment of the present invention;

[0037] Figure 6 A structural diagram of an electronic device provided for an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Figure 1 A schematic flow chart of a method provided by an exemplary embodiment of the present invention is shown, and the method comprises the following steps:

[0040] Collect the current on each side of the transformer, and calculate the instantaneous value of the adjustment current on each side according to the transformer equipment parameters, wherein the zero-sequence current is not subtracted when calculating the instantaneous value of the adjustment current on the star side of the transformer, and the adjustment current is converted to the star side when calculating the instantaneous value of the adjustment current on the angle side of the transformer;

[0041] Calculating the instantaneous value of the three-phase differential current according to the instantaneous value of the adjusted current on each side, and calculating the maximum absolute value of the instantaneous value of the three-phase differential current;

[0042] Calculating a zero-sequence differential current reference value according to the instantaneous value of the three-phase differential current and the maximum absolute value of the instantaneous value of the three-phase differential current;

[0043] According to the zero-sequence differential current reference value, the instantaneous value of the three-phase corrected differential current is calculated.

[0044] According to some preferred embodiments, the maximum absolute value of the instantaneous value of the three-phase difference current is calculated as follows:

[0045] when And when the duration reaches t1, if but when When the duration reaches t2, otherwise remain unchanged;

[0046] in, for The instantaneous value of the phase difference current, Take a, b, c to represent phase a, phase b, and phase c respectively; id_set is the differential current judgment threshold value, for The maximum absolute value of the instantaneous value of the phase difference flow, t1 is the first delay constant, and t2 is the second delay constant.

[0047] According to some preferred embodiments, the differential current judgment threshold value id_set has a value range of 0.01 to 0.25Ie, where Ie is the rated current; the first delay constant t1 has a value range of less than 5ms, and the second delay constant t2 has a value range of not less than 10ms.

[0048] According to some preferred embodiments, it further includes: calculating the minimum value id among the maximum absolute values of the instantaneous values of the three-phase differential currents min , specifically:

[0049] id min = min{ida max , idb max , idc max}.

[0050] According to some preferred embodiments, calculating the zero-sequence differential current reference value specifically includes:

[0051] Calculating the zero-sequence differential current 3id0 = ida + idb + idc;

[0052] When |3id0| > id0_set and the duration reaches t3, set the zero-sequence flag of the differential current; when |3id0| < id0_set and the duration reaches t4, clear the zero-sequence flag of the differential current; otherwise, the zero-sequence flag of the differential current remains unchanged; where, id 0_ set is the zero-sequence differential current judgment threshold value, t3 is the third delay setting value, and t4 is the fourth delay setting value;

[0053] When the zero-sequence flag of the differential current is in the set state, if id min = ida max , then the zero-sequence differential current reference value id0_ref takes the a-phase differential current, that is, id0_ref = id a ; if id min = idb max , then the zero-sequence differential current reference value id0_ref takes the b-phase differential current, that is, id0_ref = id b ; if id min = idc max , then the zero-sequence differential current reference value id0_ref takes the c-phase differential current, that is, id0_ref = id c ;

[0054] When the zero-sequence flag of the differential current is 0, then the zero-sequence differential current reference value id0_ref is set to 0, that is, id0_ref = 0.

[0055] According to some preferred embodiments, the value range of the zero-sequence differential current judgment threshold value id0_set is 0.01 - 0.25Ie, where Ie is the rated current; the value range of the third delay setting value t3 is less than 5 ms, and the value range of the fourth delay setting value t4 is not less than 10 ms.

[0056] According to some preferred embodiments, calculating the instantaneous values of the three-phase corrected differential currents based on the zero-sequence differential current reference value specifically includes:

[0057]

[0058] in, for Phase correction differential current instantaneous value, Take a, b, and c to represent phase a, phase b, and phase c respectively.

[0059] To further illustrate the accuracy and adaptability of a transformer protection longitudinal differential current correction method based on zero-sequence differential current provided by the present invention, a transformer simulation model is constructed according to the above principles. The three-phase connection clock number of the transformer is YNa0d11, the rated capacity is 900MW, the rated voltages of the high, medium and low voltage sides are 500kV, 220kV and 63.5kV respectively, and the transformation ratio of the current transformers on the high, medium and low voltage sides is 2000:1.

[0060] When simulating a phase A ground fault in the transformer protection zone, the currents on each side of the transformer are collected, such as Figure 2 According to the above transformer equipment parameters, the instantaneous value of the adjustment current is calculated, wherein the zero-sequence current is not subtracted when calculating the instantaneous value of the adjustment current on the star side of the transformer, and the instantaneous value of the adjustment current on the angle side of the transformer is converted to the star side to obtain the instantaneous value of the three-phase differential current and the zero-sequence differential current, as shown in Figure 3 As shown. Figure 3 It can be seen that during the fault period, all three phases have large differential currents, among which the maximum absolute value of the instantaneous value of the differential current of phase A is about 3.1Ie, the maximum absolute value of the instantaneous value of the differential current of phases B and C is about 0.86Ie, and the maximum absolute value of the instantaneous value of the zero-sequence differential current is about 0.5Ie. Assuming id_set = 0.1Ie, t1 = 1ms, t2 = 10ms, id0_set = 0.1Ie, t3 = 1ms, t4 = 10ms, it is calculated that during the fault process, the differential current has a zero-sequence flag set state, and then according to id min The corresponding differential current phases are calculated, and the zero-sequence differential current reference value id0_ref is about 0.86Ie. Then the instantaneous value of the three-phase corrected differential current is calculated. The maximum absolute value of the instantaneous value of the corrected differential current of the fault phase A increases to about 4Ie, and the maximum value of the instantaneous value of the corrected differential current of the non-fault phases B and C drops to below 0.03Ie. Ie is the rated current. The instantaneous value of the three-phase corrected differential current is as follows: Figure 4 shown.

[0061] Therefore, by adopting the technical solution of the present invention, it is possible to use an adjustment current without reducing the zero sequence on each side of the transformer when calculating the longitudinal differential current of the transformer, thereby increasing the differential current of the fault phase while eliminating the influence of the zero sequence differential current on the non-fault phase, thereby greatly improving the sensitivity of the longitudinal differential protection.

[0062] Figure 5 A schematic diagram of the structure of a transformer protection longitudinal differential current correction device based on zero-sequence differential current provided by an exemplary embodiment of the present invention is shown, comprising:

[0063] A data acquisition unit, used to collect currents on each side of the transformer;

[0064] A calculation unit is used to calculate the instantaneous value of the adjusted current on each side according to the transformer equipment parameters, wherein the zero-sequence current is not subtracted when calculating the instantaneous value of the adjusted current on the star side of the transformer, and the instantaneous value of the adjusted current on the corner side of the transformer is converted to the star side; the instantaneous value of the three-phase differential current is calculated according to the instantaneous value of the adjusted current on each side, and the maximum absolute value of the three-phase differential current instantaneous value is calculated; the zero-sequence differential current reference value is calculated according to the instantaneous value of the three-phase differential current and the maximum absolute value of the three-phase differential current instantaneous value; and the instantaneous value of the three-phase corrected differential current is calculated according to the zero-sequence differential current reference value.

[0065] Figure 5 The device shown can execute the aforementioned transformer protection longitudinal differential current correction method based on zero-sequence differential current according to an embodiment of the present invention.

[0066] The device performs functions similar to the method provided above. For other functions, please refer to the previous description and will not be repeated here.

[0067] Figure 6 The structure diagram of an electronic device provided by the present invention is shown, which includes a processor and a memory. The memory stores computer instructions, and when the computer instructions are executed by the processor, the processor executes the computer instructions to implement the method and detailed solution described above.

[0068] It should be understood that the above device embodiments are only illustrative, and the device disclosed in the present invention can also be implemented in other ways. For example, the division of units / modules described in the above embodiments is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units, modules or components can be combined, or can be integrated into another system, or some features can be ignored or not executed.

[0069] In addition, unless otherwise specified, each functional unit / module in each embodiment of the present invention may be integrated into one unit / module, each unit / module may exist physically separately, or two or more units / modules may be integrated together. The above-mentioned integrated unit / module may be implemented in the form of hardware or in the form of a software program module.

[0070] If the integrated unit / module is implemented in the form of hardware, the hardware may be a digital circuit, an analog circuit, etc. The physical implementation of the hardware structure includes but is not limited to transistors, memristors, etc. If not otherwise specified, the processor or chip may be any appropriate hardware processor, such as a CPU, a GPU, an FPGA, a DSP, an ASIC, etc. If not otherwise specified, the on-chip cache, the off-chip memory, and the memory may be any appropriate magnetic storage medium or magneto-optical storage medium, such as a resistive random access memory RRAM (Resistive Random Access Memory), a dynamic random access memory DRAM (Dynamic Random Access Memory), a static random access memory SRAM (Static Random-Access Memory), an enhanced dynamic random access memory EDRAM (Enhanced Dynamic Random Access Memory), a high-bandwidth memory HBM (High-Bandwidth Memory), a hybrid memory cube HMC (Hybrid Memory Cube), etc.

[0071] If the integrated unit / module is implemented in the form of a software program module and sold or used as an independent product, it can be stored in a computer-readable memory. Based on this 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, which is stored in a memory and includes several instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present disclosure. The aforementioned memory includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes.

[0072] An embodiment of the present invention further provides a non-transitory computer storage medium storing a computer program. When the computer program is executed by multiple processors, the processors execute the method and the refined scheme described above.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be included in the scope of the claims.

Claims

1. A transformer protection longitudinal differential current correction method based on zero-sequence differential current, characterized in that: It includes the following steps: Collect the currents on each side of the transformer, and calculate the instantaneous value of the adjusted current on each side according to the transformer equipment parameters. When calculating the instantaneous value of the adjusted current on the star side of the transformer, the zero-sequence current is not subtracted. When calculating the instantaneous value of the adjusted current on the delta side of the transformer, it is converted to the star side. Calculate the instantaneous value of the three-phase differential current according to the instantaneous values of the adjusted currents on each side, and calculate the maximum absolute value of the instantaneous values of the three-phase differential current. Calculate the zero-sequence differential current reference value according to the instantaneous values of the three-phase differential current and the maximum absolute value of the instantaneous values of the three-phase differential current. Calculate the instantaneous value of the three-phase corrected differential current according to the zero-sequence differential current reference value.

2. A transformer protection longitudinal differential current correction method based on zero-sequence differential current as claimed in claim 1, characterized in that: The specific calculation of the maximum absolute value of the instantaneous values of the three-phase differential current is as follows: when And when the duration reaches t1, if but when When the duration reaches t2, otherwise remain unchanged; in, for The instantaneous value of the phase difference current, Take a, b, c to represent phase a, phase b, and phase c respectively; id_set is the differential current judgment threshold value, for The maximum absolute value of the instantaneous value of the phase difference flow, t1 is the first delay constant, and t2 is the second delay constant.

3. A transformer protection longitudinal differential current correction method based on zero-sequence differential current as claimed in claim 2, characterized in that: The value range of the differential current judgment threshold id_set is 0.01 - 0.25Ie, where Ie is the rated current; the value range of the first delay setting value t1 is less than 5ms, and the value range of the second delay setting value t2 is not less than 10ms.

4. A transformer protection longitudinal differential current correction method based on zero-sequence differential current as claimed in claim 2, characterized in that: It also includes: Calculate the minimum value id among the maximum absolute values ​​of the instantaneous values ​​of the three-phase difference current min , specifically id min =min{ida max , idb max , idc max }.

5. A transformer protection longitudinal differential current correction method based on zero-sequence differential current as claimed in claim 4, characterized in that: The specific calculation of the zero-sequence differential current reference value is as follows: Calculate the zero-sequence differential current 3id0 = ida + idb + idc; When |3id0| > id0_set and the duration reaches t3, set the zero-sequence flag of the differential current; when |3id0| < id0_set and the duration reaches t4, clear the zero-sequence flag of the differential current; otherwise, the zero-sequence flag of the differential current remains unchanged. Here, id0_set is the zero-sequence differential current judgment threshold, t3 is the third delay setting value, and t4 is the fourth delay setting value. When the differential current has a zero sequence flag set, if id min =ida max , then the zero-sequence differential current reference value id0_ref takes the phase differential current, that is, id0_ref = id a ; If id min =idb max , then the zero-sequence differential current reference value id0_ref takes the b-phase differential current, that is, id0_ref = id b ; If id min =idc max , then the zero-sequence differential current reference value id0_ref takes the c-phase differential current, that is, id0_ref = id c ; When the zero-sequence flag of the differential current is not in the set state, the zero-sequence differential current reference value id0_ref is set to 0, that is, id0_ref = 0.

6. A transformer protection longitudinal differential current correction method based on zero-sequence differential current as claimed in claim 5, characterized in that: The value range of the zero-sequence differential current judgment threshold id0_set is 0.01 - 0.25Ie, where Ie is the rated current; the value range of the third delay setting value t3 is less than 5ms, and the value range of the fourth delay setting value t4 is not less than 10ms.

7. A transformer protection longitudinal differential current correction method based on zero-sequence differential current as claimed in claim 5, characterized in that: The specific calculation of the instantaneous value of the three-phase corrected differential current according to the zero-sequence differential current reference value is as follows: in, for Phase correction differential current instantaneous value, Take a, b, and c to represent phase a, phase b, and phase c respectively.

8. A transformer protection longitudinal differential current correction device based on zero-sequence differential current, characterized in that: It includes: A data acquisition unit for collecting the currents on each side of the transformer. A calculation unit for calculating the instantaneous value of the adjusted current on each side according to the transformer equipment parameters. When calculating the instantaneous value of the adjusted current on the star side of the transformer, the zero-sequence current is not subtracted. When calculating the instantaneous value of the adjusted current on the delta side of the transformer, it is converted to the star side. Calculate the instantaneous value of the three-phase differential current according to the instantaneous values of the adjusted currents on each side, and calculate the maximum absolute value of the instantaneous values of the three-phase differential current. Calculate the zero-sequence differential current reference value according to the instantaneous values of the three-phase differential current and the maximum absolute value of the instantaneous values of the three-phase differential current. Calculate the instantaneous value of the three-phase corrected differential current according to the zero-sequence differential current reference value.

9. An electronic device, characterized in that: It includes: A processor; And A memory storing computer instructions, which when executed by the processor, cause the processor to execute the method according to any one of claims 1 - 7.

10. A non-transitory computer storage medium storing a computer program, which when executed by multiple processors, causes the processors to execute the method according to any one of claims 1 - 7.

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