Substation main transformer high and low voltage side dominant harmonic source identification method

Abstract

The invention discloses a transformer substation main transformer high and low voltage side dominant harmonic source identification method, which comprises the following steps: collecting electric energy quality monitoring data of a main transformer high and low voltage side in a power grid operation state; the power quality monitoring data comprises a power supply bus fundamental wave voltage measured value, a power supply bus concerned frequency harmonic voltage measured value and incoming and outgoing line concerned frequency harmonic current measured values; on the basis of the established equivalent impedance model, a calculated value of power supply bus concerned frequency harmonic voltage is obtained in combination with incoming and outgoing line concerned frequency harmonic current measured values; calculating the measured value and the calculated value of the concerned frequency harmonic voltage content ratio of each side power supply bus independently caused by the harmonic current of the high-voltage side injection system and the low-voltage side injection system; comparing the measured value and the calculated value of the concerned frequency harmonic voltage content ratio of the power supply bus at each side, and identifying a dominant influence source of the harmonic voltage of the power supply bus at each side; according to the invention, the dominant harmonic source at the high-voltage and low-voltage sides of the main transformer of the transformer substation is identified.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a method for identifying dominant harmonic sources on high-voltage and low-voltage sides of a main transformer in a substation. Background Art

[0002] With the development of the national economy and the improvement of people's living standards, power electronic devices and high-energy nonlinear equipment are widely used in power grids. This has led to a continuous increase in the amount of harmonics injected into the grid, and the increasingly prominent problem of harmonic pollution. This not only endangers the safe, stable and economic operation of the power grid, but also affects the normal production of other users on the grid. At the same time, adhering to the power quality management principle of "polluter, payer," accurately identifying and locating the dominant harmonic sources on the high- and low-voltage sides of substation main transformers has become an urgent need to ensure the healthy operation of the power grid and protect the rights and interests of all users. Existing harmonic source tracing methods mainly include the harmonic active power direction method, correlation analysis method, and fluctuation quantity method. Among them, the harmonic active power direction method requires that there is only one harmonic source or a strong dominant harmonic source; the correlation analysis method requires that there is only one harmonic source or a strong dominant harmonic source, the harmonic voltage and harmonic current at the PCC are continuous, independent of each other, and the sample capacity is sufficient. The measured line must be a non-no-load line, and the harmonic current cannot be too small; the fluctuation quantity method requires that the harmonic impedance does not change or fluctuates only in a small range, and only the harmonic source on the system side or the user side fluctuates. At present, the main problems with the existing harmonic source tracing methods are: on the one hand, traditional harmonic source tracing methods mostly rely on complex harmonic flow calculations, and need to calculate the amplitude and phase angle of harmonic voltages and currents at the same voltage level or across voltage levels at multiple nodes. The calculation process is cumbersome and time-consuming, and is easily affected by factors such as model accuracy and parameter changes. The mechanism is complex and is limited to specific application scenarios, resulting in the accuracy and adaptability of traditional methods being difficult to meet actual needs. On the other hand, power quality monitoring technology has made great progress, providing convenient conditions for obtaining massive harmonic monitoring data. However, the application potential of monitoring data in harmonic source tracing analysis on the high and low voltage sides of substation main transformers has not been fully explored.

[0003] In the related art, the patent application document with publication number CN118501542A mainly uses the change of the grid operation mode to identify the dominant harmonic sources of all feeder lines (i.e., all harmonic sources) at the same voltage level, but cannot identify the dominant harmonic sources on the high and low voltage sides of the substation main transformer across voltage levels. The patent application document with publication number CN119154297A mainly uses the switching transformation of passive filters to quantify the harmonic contribution rate of all transmission lines (i.e., all harmonic sources) at the same voltage level, but also cannot identify the dominant harmonic sources on the high and low voltage sides of the substation main transformer across voltage levels. Moreover, the above-mentioned identification scheme requires multiple changes in the grid operation mode or multiple switching transformations of passive filters, requires a large amount of power quality monitoring data from the grid company and other cooperation work, and the operation process is complicated and coordination is difficult.

[0004] Therefore, how to make full use of the harmonic monitoring data on the high and low voltage sides of the substation main transformer and identify the dominant harmonic sources on the high and low voltage sides of the substation main transformer in combination with the system topology and grid parameters is a key technical problem that needs to be solved urgently. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to identify the dominant harmonic sources on the high and low voltage sides of the main transformer of a substation.

[0006] The present invention solves the above technical problems through the following technical means:

[0007] A method for identifying dominant harmonic sources on the high and low voltage sides of a substation main transformer is proposed. The method includes:

[0008] Collect power quality monitoring data on the high and low voltage sides of the main transformer when the power grid is in operation, including the measured value of the fundamental voltage of the power supply bus, the measured value of the harmonic voltage of the power supply bus at the frequency of concern, and the measured value of the harmonic current of the incoming and outgoing lines at the frequency of concern;

[0009] Based on the constructed equivalent impedance model and combined with the measured values of the harmonic currents of the incoming and outgoing lines at the frequencies of interest, the calculated values of the harmonic voltages of the power supply bus at the frequencies of interest are obtained;

[0010] Calculate the measured and calculated values of the harmonic voltage content of the power supply busbars at the frequencies of interest caused by the harmonic currents injected into the system on the high-voltage and low-voltage sides;

[0011] Compare the measured and calculated values of the harmonic voltage content of the concerned frequencies of the power supply busbars on each side to identify the dominant influencing sources of the harmonic voltage of the power supply busbars on each side.

[0012] Furthermore, the acquisition of power quality monitoring data on the high and low voltage sides of the main transformer in the grid operation state includes:

[0013] Based on the measurement points on the high-voltage side and the low-voltage side of the main transformer, the discrete time-domain signals of the voltage and current on each side within the same time period are synchronously sampled;

[0014] According to the discrete time domain signals of voltage and current on each side, the measured values of fundamental voltage of the power supply bus on each side, the measured values of harmonic voltage at the frequency of interest of the power supply bus and the measured values of harmonic current at the frequency of interest of the incoming and outgoing lines are obtained.

[0015] Furthermore, the measuring points on the high-voltage side include a high-voltage side voltage measuring point and a high-voltage side current measuring point. The high-voltage side voltage measuring point is set on the high-voltage side power supply bus, and the high-voltage side current measuring point is set on the high-voltage side transmission line close to the high-voltage side power supply bus. The current direction is the positive direction out of the high-voltage side power supply bus.

[0016] The measuring points on the low-voltage side include a low-voltage side voltage measuring point and a low-voltage side current measuring point; the low-voltage side voltage measuring point is set on the low-voltage side power supply bus, and the low-voltage side current measuring point is set on the low-voltage side transmission line close to the low-voltage side power supply bus, and the current direction is the positive direction out of the low-voltage side power supply bus.

[0017] Furthermore, the method of obtaining the measured value of the fundamental voltage of the power supply bus on each side, the measured value of the harmonic voltage at the frequency of interest of the power supply bus, and the measured value of the harmonic current at the frequency of interest of the incoming and outgoing lines on each side based on the time-domain discrete signals of the voltage on each side and the time-domain discrete signals of the current on each side includes:

[0018] The discrete time domain signals of voltage and current on each side are converted into frequency domain representations, and based on the frequency domain representations, the measured values of the fundamental voltage of the power supply bus on each side, the measured values of the harmonic voltage of the power supply bus at the frequency of interest, and the measured values of the harmonic current of the incoming and outgoing lines at the frequency of interest are obtained.

[0019] Furthermore, the equivalent impedance model is constructed based on the short-circuit capacity of the system on each side of the main transformer and the rated voltage on each side. The equivalent harmonic impedance of the system on each side of the equivalent impedance model is:

[0020]

[0021] Where S M,H is the short-circuit capacity of the high-voltage side system, S M,L is the short-circuit capacity of the low-voltage side system, U M,H is the rated voltage on the high voltage side, U M,L is the rated voltage of the low voltage side, Z H,h is the hth order equivalent harmonic impedance of the high voltage side system, Z L,h is the hth equivalent harmonic impedance of the low-voltage side system, and h is the harmonic order.

[0022] Furthermore, the equivalent impedance model established is combined with the measured values of the harmonic currents of the incoming and outgoing lines at the frequencies of interest to obtain the calculated values of the harmonic voltages of the power supply bus at the frequencies of interest, including:

[0023] According to the measured RMS value of the hth harmonic current of the incoming and outgoing lines on each side and the equivalent harmonic impedance of the system on each side, the calculated value of the harmonic voltage of the power supply bus at the frequency of interest is obtained, which is expressed as:

[0024] U′ H,h =I H,h Z H,h

[0025] U′ L,h =I L,h Z L,h

[0026] Where U′ H,h The root mean square value of the calculated value of the hth harmonic voltage of the power supply busbar on the high-voltage side of the main transformer, I H,h is the root mean square value of the measured value of the hth harmonic current on the high-voltage side of the main transformer, U′ L,h The root mean square value of the calculated value of the hth harmonic voltage of the power supply busbar on the low-voltage side of the main transformer, I L,h It is the RMS value of the measured value of the hth harmonic current on the low-voltage side of the main transformer.

[0027] Furthermore, the calculation of the measured and calculated values of the harmonic voltage content rate of the power supply bus at the frequency of interest caused by the harmonic current injected into the system on the high-voltage side and the low-voltage side includes:

[0028] The measured and calculated values of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest when the high-voltage side harmonic voltage acts alone are:

[0029]

[0030] Where, β H,h is the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, β′ H,h is the calculated value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, U H,h is the root mean square value of the measured value of the hth harmonic voltage on the high voltage side, U′ H,h is the root mean square value of the calculated value of the hth harmonic voltage on the high voltage side, U H,1 is the RMS value of the measured fundamental voltage on the high-voltage side;

[0031] When calculating the harmonic voltage on the low-voltage side alone, the measured and calculated values of the harmonic voltage content rate of the low-voltage power supply bus at the frequency of interest are:

[0032]

[0033] Where, β L,h is the measured value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, U L,h is the root mean square value of the measured value of the hth harmonic voltage on the low voltage side; U′ L,h is the root mean square value of the calculated value of the hth harmonic voltage on the low voltage side; U L,1 It is the RMS value of the measured fundamental voltage on the low-voltage side.

[0034] Furthermore, the comparison of the measured value and the calculated value of the harmonic voltage content rate of the power supply busbars at the concerned frequencies on each side and the identification of the dominant influencing source of the harmonic voltage of the power supply busbars at each side includes:

[0035] The ratio between the measured value of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest and the calculated value of its voltage content rate is compared with the set first upper limit threshold and first lower limit threshold to identify the dominant influencing source of the harmonic voltage of the high-voltage side power supply bus;

[0036] The ratio between the measured value of the harmonic voltage content rate of the low-voltage side power supply bus at the frequency of interest and the calculated value of its voltage content rate is compared with the set second upper limit threshold and second lower limit threshold to identify the dominant influencing source of the harmonic voltage of the low-voltage side power supply bus.

[0037] Furthermore, the method of comparing the ratio between the measured value of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest and the calculated value of the voltage content rate thereof with the set first upper limit threshold and first lower limit threshold to identify the dominant influencing source of the harmonic voltage of the high-voltage side power supply bus includes:

[0038] when When , it is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by background harmonics;

[0039] when When , it is determined that the hth harmonic voltage of the power supply busbar on the high voltage side is dominated by the harmonic current of the nonlinear load on the low voltage side;

[0040] when When, if It is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by the background harmonic; if It is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load; if It is determined that the hth harmonic voltage of the power supply bus on the high-voltage side is dominated by the background harmonic and the harmonic current of the nonlinear load on the low-voltage side;

[0041] Among them, β H,his the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, β′ H,h is the calculated value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, for and β H,h The phase difference, θ is β H,h and β′ L,h The phase difference, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, ε max,1 is the first upper threshold, ε min,1 is the first lower threshold.

[0042] Furthermore, the method of comparing the ratio between the measured value of the harmonic voltage content rate of the low-voltage side power supply bus at the frequency of interest and the calculated value of the voltage content rate thereof with the set second upper threshold and second lower threshold to identify the dominant influencing source of the harmonic voltage of the low-voltage side power supply bus includes:

[0043] when When , it is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by background harmonics;

[0044] when When , it is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load;

[0045] when When, if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by background harmonics; if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load; if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the background harmonic and the low-voltage side nonlinear load harmonic current;

[0046] Among them, β L,h is the measured value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, for and β H,h The phase difference, θ is β H,h and β′ L,h The phase difference, β H,h is the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, ε max,2 is the second upper threshold, ε min,2is the second lower threshold.

[0047] The advantages of the present invention are:

[0048] (1) The present invention is based on a data-model joint driving method, with the power quality monitoring data of the high and low voltage sides of the substation main transformer monitored in real time as data driving, and the substation equivalent impedance model as model driving, and jointly calculates the measured value and calculated value of the harmonic responsibility of the high-voltage side power supply bus harmonic voltage caused by the high-voltage side harmonic voltage alone, and the measured value and calculated value of the harmonic responsibility of the low-voltage side power supply bus harmonic voltage caused by the low-voltage side harmonic voltage alone. The measured value and calculated value of the harmonic responsibility of the high-voltage side power supply bus harmonic voltage are compared respectively, and the measured value and calculated value of the harmonic responsibility of the low-voltage side power supply bus harmonic voltage are compared respectively, so as to identify the dominant harmonic sources of the high and low voltage sides of the main transformer; the present invention only needs to identify the flow direction of the harmonic flow of the substation main transformer (that is, whether it flows from the high-voltage side to the low-voltage side, or from the low-voltage side to the high-voltage side), and does not require complex harmonic flow calculation.

[0049] (2) The present invention can quantitatively analyze the contribution of the harmonic sources on the high-voltage and low-voltage sides of the substation main transformer to the harmonic voltage of the power supply bus when they act alone, and use specific numerical calculations to accurately identify the dominant harmonic sources on the high-voltage and low-voltage sides of the main transformer. It can provide theoretical support for harmonic source positioning and harmonic responsibility division, provide a scientific basis for power grid harmonic management, and promote the clean, efficient and sustainable development of new power systems.

[0050] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A schematic flow chart of a method for identifying dominant harmonic sources on the high and low voltage sides of a main transformer in a substation, proposed in one embodiment of the present invention;

[0052] Figure 2 Schematic diagram of the locations of harmonic voltage and harmonic current sampling points in one embodiment of the present invention;

[0053] Figure 3 The equivalent impedance model of the high and low voltage sides of the main transformer of the substation in one embodiment of the present invention;

[0054] Figure 4 A vector superposition diagram of the harmonic voltage of the high-voltage side power supply bus and the harmonic voltage of the low-voltage side power supply bus in one embodiment of the present invention;

[0055] Figure 5 FIG. 1 is a topological diagram of a substation in an embodiment of the present invention. DETAILED DESCRIPTION

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0057] like Figure 1 As shown, an embodiment of the present invention proposes a method for identifying the dominant harmonic sources on the high and low voltage sides of a main transformer in a substation, the method comprising the following steps:

[0058] S10, collecting power quality monitoring data on the high and low voltage sides of the main transformer when the power grid is in operation, the power quality monitoring data including the measured value of the fundamental voltage of the power supply bus, the measured value of the harmonic voltage of the power supply bus at the frequency of concern, and the measured value of the harmonic current of the incoming and outgoing lines at the frequency of concern;

[0059] S20. Based on the constructed equivalent impedance model and in combination with the measured values of the harmonic currents of the incoming and outgoing lines at the frequencies of interest, the calculated values of the harmonic voltages of the power supply bus at the frequencies of interest are obtained;

[0060] S30. Calculate the measured and calculated values of the harmonic voltage content of the power supply busbars at the frequencies of interest caused by the harmonic currents injected into the system on the high-voltage side and the low-voltage side;

[0061] S40. Compare the measured value and calculated value of the harmonic voltage content rate of the concerned frequency of the power supply bus on each side, and identify the dominant influencing source of the harmonic voltage of the power supply bus on each side.

[0062] It should be noted that this embodiment only needs to collect the power quality monitoring data of the high and low voltage sides of the substation main transformer under a random power grid operating state, and combine the simple system topology and a small number of grid parameters to calculate the harmonic voltage content of the high and low voltage sides of the substation main transformer at the frequency of concern, as well as the harmonic voltage content of the power supply bus on each side caused by the harmonic current injected into the system on each side. Then, by comparing the harmonic voltage content of the high-voltage side at the frequency of concern with the harmonic voltage content of the high-voltage side power supply bus caused by the harmonic current injected into the system on the high-voltage side, the dominant harmonic source on the high-voltage side can be identified. By comparing the harmonic voltage content of the low-voltage side at the frequency of concern with the harmonic voltage content of the high and low voltage side power supply bus caused by the harmonic current injected into the system on the low-voltage side, the dominant harmonic source on the low-voltage side can be identified.

[0063] As a further preferred technical solution, step S10: collecting power quality monitoring data on the high and low voltage sides of the main transformer in the grid operation state, specifically includes the following steps:

[0064] S11. Based on the measuring points on the high-voltage side and the low-voltage side of the main transformer, synchronously sample the discrete time-domain signals of the voltage and current on each side within the same time period;

[0065] Specifically, if Figure 2 As shown, the measuring points on the high-voltage side include a high-voltage side voltage measuring point 1 and a high-voltage side current measuring point 1. The high-voltage side voltage measuring point 1 is set on the high-voltage side power supply bus, and the high-voltage side current measuring point 1 is set on the high-voltage side transmission line close to the high-voltage side power supply bus. The current direction is the positive direction out of the high-voltage side power supply bus;

[0066] The measuring points on the low-voltage side include a low-voltage side voltage measuring point 2 and a low-voltage side current measuring point 2; the low-voltage side voltage measuring point 2 is set on the low-voltage side power supply bus, and the low-voltage side current measuring point 2 is set on the low-voltage side transmission line close to the low-voltage side power supply bus, and the current direction is the positive direction out of the low-voltage side power supply bus.

[0067] Specifically, the voltage time domain discrete signals u on each side of the main transformer are synchronously sampled in the same time period. H (n),u L (n), the discrete time domain signal i of the current on each side of the main transformer H (n), i L (n), where n is the number of the sampled voltage and current waveform time domain discrete signal, H and L represent the high and low voltage sides of the main transformer, respectively, and the window width is set to 10 cycles.

[0068] S12. According to the discrete time domain signals of voltage and current on each side, the measured values of the fundamental voltage of the power supply bus on each side, the measured values of the harmonic voltage at the frequency of interest of the power supply bus, and the measured values of the harmonic current at the frequency of interest of the incoming and outgoing lines are obtained.

[0069] Specifically, this embodiment obtains the root mean square value of the measured value of the fundamental voltage of the power supply bus on each side, the root mean square value of the measured value of the harmonic voltage of the power supply bus at the frequency of interest, and the root mean square value of the measured value of the harmonic current of the incoming and outgoing lines at the frequency of interest based on the time-domain discrete signals of the voltage on each side and the time-domain discrete signals of the current on each side. The calculation formula is:

[0070]

[0071]

[0072] Where, A is the fundamental voltage phasor on the high voltage side of the main transformer; u,H,1 is the real part of the fundamental voltage phasor on the high voltage side of the main transformer; B u,H,1 is the imaginary part of the fundamental voltage phasor on the high-voltage side of the main transformer; Is the fundamental voltage phasor of the low-voltage side of the main transformer; A u,L,1is the real part of the fundamental voltage phasor on the low-voltage side of the main transformer; B u,L,1 The imaginary part of the fundamental voltage phasor on the low-voltage side of the main transformer; U H,1 is the RMS value of the fundamental voltage on the high-voltage side of the main transformer; U L,1 The RMS value of the fundamental voltage on the low-voltage side of the main transformer; is the hth harmonic voltage phasor on the high-voltage side of the main transformer; A u,H,h B is the real part of the hth harmonic voltage phasor on the high-voltage side of the main transformer; u,H,h is the imaginary part of the hth harmonic voltage phasor on the high-voltage side of the main transformer; is the hth harmonic voltage phasor on the low-voltage side of the main transformer; A u,L,h B is the real part of the hth harmonic voltage phasor on the low-voltage side of the main transformer; u,L,h is the imaginary part of the hth harmonic voltage phasor on the low-voltage side of the main transformer; is the hth harmonic current phasor on the high-voltage side of the main transformer; A i,H,h B is the real part of the hth harmonic current phasor on the high-voltage side of the main transformer; i,H,h is the imaginary part of the hth harmonic current phasor on the high-voltage side of the main transformer; is the hth harmonic current phasor on the low-voltage side of the main transformer; A i,L,h B is the real part of the hth harmonic current phasor on the low-voltage side of the main transformer; i,L,h is the imaginary part of the hth harmonic current phasor on the low-voltage side of the main transformer; U H,h The root mean square value of the hth harmonic voltage on the high-voltage side of the main transformer (measured value); U L,h The root mean square value of the hth harmonic voltage on the low-voltage side of the main transformer (measured value); I H,h is the root mean square value of the hth harmonic current on the high-voltage side of the main transformer; I L,h is the root mean square value of the hth harmonic current on the low-voltage side of the main transformer; h is the harmonic order; N is the number of sampling points of 10 cycles of the time-domain discrete signal of the harmonic voltage or current waveform; n is the number of the time-domain discrete signal, ranging from 0 to N-1; j is the imaginary unit; and e is a natural constant.

[0073] It should be noted that this embodiment converts the sampled time-domain discrete signals of the voltage on each side and the sampled time-domain discrete signals of the current on each side from time domain representation to frequency domain representation through discrete Fourier transform, that is, the collected time-domain discrete signals of the high- and low-voltage sides of the main transformer are converted into the frequency domain using discrete Fourier transform, and the root mean square value of the fundamental voltage and the root mean square values of the harmonic voltage and current of the frequency of interest are calculated in the frequency domain.

[0074] As a further preferred technical solution, Figure 3 As shown in FIG, the equivalent impedance model is constructed based on the system short-circuit capacity and rated voltage of each side of the main transformer, wherein: Figure 3 Shown Z Trepresents the main transformer impedance. The equivalent harmonic impedance of each side of the equivalent impedance model is:

[0075]

[0076] Where S M,H is the short-circuit capacity of the high-voltage side system, S M,L is the short-circuit capacity of the low-voltage side system, U M,H is the rated voltage on the high voltage side, U M,L is the rated voltage of the low voltage side, Z H,h is the hth order equivalent harmonic impedance of the high voltage side system, Z L,h is the hth equivalent harmonic impedance of the low-voltage side system, and h is the harmonic order.

[0077] It should be noted that the equivalent impedance model constructed in this embodiment has a simple structure and only needs to obtain the system short-circuit capacity and rated voltage, and requires few grid parameters.

[0078] As a further preferred technical solution, step S20: based on the constructed equivalent impedance model and combined with the measured values of the harmonic currents of the incoming and outgoing lines at the frequencies of interest, obtaining the calculated values of the harmonic voltages of the power supply bus at the frequencies of interest, specifically includes:

[0079] like Figure 3 As shown in the figure, based on the root mean square value of the hth harmonic current measured by the incoming and outgoing lines on each side and the equivalent harmonic impedance of the system on each side, the calculated value of the harmonic voltage of the power supply bus at the frequency of interest is obtained, which is publicly expressed as:

[0080] U′ H,h =I H,h Z H,h

[0081] U′ L,h =I L,h Z L,h

[0082] Where U′ H,h The root mean square value of the calculated value of the hth harmonic voltage of the power supply busbar on the high-voltage side of the main transformer, I H,h is the root mean square value of the measured value of the hth harmonic current on the high-voltage side of the main transformer, U′ L,h The root mean square value of the calculated value of the hth harmonic voltage of the power supply busbar on the low-voltage side of the main transformer, I L,h It is the RMS value of the measured value of the hth harmonic current on the low-voltage side of the main transformer.

[0083] As a further preferred technical solution, step S30: calculating the measured value and calculated value of the harmonic voltage content rate of the power supply bus at the frequency of interest caused by the harmonic current injected into the system on the high-voltage side and the low-voltage side, specifically includes the following steps:

[0084] S31. Calculate the measured and calculated values of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest when the high-voltage side harmonic voltage acts alone:

[0085]

[0086] Where, β H,h is the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, β′ H,h is the calculated value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, U H,h is the root mean square value of the measured value of the hth harmonic voltage on the high voltage side, U′ H,h is the root mean square value of the calculated value of the hth harmonic voltage on the high voltage side, U H,1 is the RMS value of the measured fundamental voltage on the high-voltage side;

[0087] S32. Calculate the measured and calculated values of the harmonic voltage content rate of the low-voltage side power supply bus at the frequency of interest when the low-voltage side harmonic voltage acts alone:

[0088]

[0089] Where, β L,h is the measured value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, U L,h is the root mean square value of the measured value of the hth harmonic voltage on the low voltage side; U′ L,h is the root mean square value of the calculated value of the hth harmonic voltage on the low voltage side; U L,1 It is the RMS value of the measured fundamental voltage on the low-voltage side.

[0090] It should be noted that this embodiment calculates the ratio of the measured harmonic voltage on the high-voltage side of the main transformer to the measured fundamental voltage on the high-voltage side to indicate the measured value of the hth harmonic voltage content of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone. This calculation also indicates the calculated value of the hth harmonic voltage content of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone by calculating the ratio of the calculated harmonic voltage on the high-voltage side of the main transformer to the measured fundamental voltage on the high-voltage side. By calculating the ratio of the measured and calculated harmonic voltage content, this preparation is made to identify the dominant harmonic source on the high-voltage side of the main transformer. Similarly, similar calculations are performed on the low-voltage side.

[0091] In this embodiment, the measured value of the harmonic voltage content calculated represents the actual harmonic voltage content of the power supply bus on that side; the calculated value of the harmonic voltage content represents the harmonic voltage content of the power supply bus on that side caused solely by the harmonic current injected into the system on that side (note: the current injected into the system is generated by the nonlinear load on the low-voltage side). Therefore, in this embodiment, the direction of the harmonic flow can be determined by simply comparing the measured and calculated harmonic voltage content on the high-voltage and low-voltage sides of the substation main transformer, reducing the complex and tedious calculation process.

[0092] As a further preferred technical solution, step S40: comparing the measured value and calculated value of the harmonic voltage content rate of the power supply bus at each side to identify the dominant influencing source of the harmonic voltage of the power supply bus at each side, specifically includes the following steps:

[0093] S41. Compare the ratio between the measured value of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest and the calculated value of its voltage content rate with the set first upper threshold and first lower threshold to identify the dominant influencing source of the harmonic voltage of the high-voltage side power supply bus;

[0094] S42. Compare the ratio between the measured value of the harmonic voltage content rate of the low-voltage side power supply bus at the frequency of interest and the calculated value of its voltage content rate with the set second upper limit threshold and second lower limit threshold to identify the dominant influencing source of the harmonic voltage of the low-voltage side power supply bus.

[0095] As a further preferred technical solution, step S41: comparing the ratio between the measured value of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest and the calculated value of its voltage content rate with the set first upper threshold and first lower threshold to identify the dominant influencing source of the harmonic voltage of the high-voltage side power supply bus, specifically includes:

[0096] when When , it is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by background harmonics;

[0097] when When , it is determined that the hth harmonic voltage of the power supply busbar on the high voltage side is dominated by the harmonic current of the nonlinear load on the low voltage side;

[0098] when When, if It is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by the background harmonic; if It is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load; if It is determined that the hth harmonic voltage of the power supply bus on the high-voltage side is dominated by the background harmonic and the harmonic current of the nonlinear load on the low-voltage side;

[0099] Among them, β H,his the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, β′ H,h is the calculated value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, for and β H,h The phase difference, θ is β H,h and β′ L,h The phase difference, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, ε max,1 is the first upper threshold, ε min,1 is the first lower threshold.

[0100] It should be noted that if Figure 4 As shown, when When the hth harmonic voltage of the high-voltage side power supply bus is transmitted to the low-voltage side, the hth harmonic voltage generated is superimposed on the hth harmonic voltage on the low-voltage side. The calculation formula is as follows:

[0101]

[0102] In the formula, the superposition result for and β H,h Phase difference; β H,h is the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone; β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone; θ is β H,h and β′ L,h The phase difference is generally 20°.

[0103] Specifically, ε max,1 β H,h and β′ H,h The upper limit threshold of the ratio is 10 in practical applications; min,1 β H,h and β′ H,h The lower limit threshold of the ratio is recommended to be 2 in practical applications.

[0104] It should be noted that when When , the harmonic voltage content of the power supply bus on this side caused by the harmonic current injected into the high-voltage side system alone is much smaller than the actual content of the harmonic voltage of the power supply bus on the high-voltage side. It is judged that the harmonic voltage content of the power supply bus on this side is not caused by the harmonic current injected into the high-voltage side system as the dominant factor. Therefore, the harmonic current of the nonlinear load on the low-voltage side is not the dominant harmonic source, and the background harmonic is the dominant harmonic source. When When , the harmonic voltage content of the power supply bus on this side caused by the harmonic current injected into the high-voltage side system alone is not much different from the actual content of the harmonic voltage of the power supply bus on the high-voltage side. It is judged that the harmonic voltage content of the power supply bus on this side is caused by the harmonic current injected into the high-voltage side system. Therefore, the harmonic current of the nonlinear load on the low-voltage side is the dominant harmonic source, and the background harmonic is not the dominant harmonic source. When When the simple ratio method cannot be used to determine the dominant harmonic source, the projection method is used to quantify the dominant harmonic source on the high and low voltage sides of the substation main transformer.

[0105] That is to say, when the harmonic voltage content on the changed side caused by the harmonic current injected into the system on the same side is much smaller than the measured harmonic voltage content, the background harmonic source is dominant; when the harmonic voltage content on the changed side caused by the harmonic current injected into the system on the same side is similar to the measured harmonic voltage content, the harmonic current of the nonlinear load on the low-voltage side is dominant; when it cannot be judged, the projection method is used, and the harmonic source with a larger proportion is the dominant harmonic source, thus avoiding complex models and calculation processes.

[0106] As a further preferred technical solution, step S42: comparing the ratio between the measured value of the harmonic voltage content rate of the low-voltage side power supply bus at the frequency of interest and the calculated value of its voltage content rate with the set second upper threshold and second lower threshold to identify the dominant influencing source of the harmonic voltage of the low-voltage side power supply bus, specifically includes:

[0107] when When , it is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by background harmonics;

[0108] when When , it is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load;

[0109] when When, if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by background harmonics; if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load; if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the background harmonic and the low-voltage side nonlinear load harmonic current;

[0110] Among them, β L,h is the measured value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, for and β H,h The phase difference, θ is β H,hand β′ L,h The phase difference, β H,h is the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, ε max,2 is the second upper threshold, ε min,2 is the second lower threshold.

[0111] Among them, ε max,2 β L,h and β′ L,h The upper limit threshold of the ratio is 10 in practical applications; min,2 β L,h and β′ L,h The lower limit threshold of the ratio is recommended to be 2 in practical applications.

[0112] In order to better describe the present invention, a specific embodiment is described in detail below:

[0113] The system topology of a 220kV substation is as follows Figure 5 As shown in Figure 1, at the high and low voltage sides of the main transformer, that is, at voltage and current measuring points 1 and 2, the fundamental voltage root mean square value of the power supply busbar on the high and low voltage sides of the substation main transformer, the fifth harmonic voltage root mean square value of the power supply busbar on the high and low voltage sides, and the fifth harmonic current root mean square value of the incoming and outgoing lines are synchronously collected at the same time. The specific results are shown in Table 1.

[0114] Table 1 Measurement values of fundamental wave and 5th harmonic voltage and current of power supply busbar on high and low voltage sides

[0115] <![CDATA[U H,1 (kV)]]> <![CDATA[U L,1 (kV)]]> <![CDATA[U H,5 (kV)]]> <![CDATA[U L,5 (kV)]]> <![CDATA[I H,5 (A)]]> <![CDATA[I L,5 (A)]]> 134.67 66.82 1.50 1.25 10.50 21.00

[0116] Obtain the short-circuit capacity S of the high and low voltage side systems M,H =18175MVA, S M,L =3415MVA, rated voltage of high and low voltage sides U M,H =220kV, U M,L =110kV, calculate the 5th equivalent harmonic impedance of the high and low voltage side systems and the 5th harmonic RMS value of the power supply bus voltage, as shown in Table 2.

[0117] Table 2 Calculated values of the fifth equivalent harmonic impedance and fifth harmonic voltage of the high and low voltage side systems

[0118] <![CDATA[Z H,5 (Oh)]]> <![CDATA[Z L,5 (Oh)]]> <![CDATA[U′ H,5 (kV)]]> <![CDATA[U′ L,5 (kV)]]> 2.66 3.54 0.139 0.372

[0119] The measured and calculated values of the 5th harmonic voltage content rate of the high-voltage side power supply bus when the 5th harmonic voltage on the high-voltage side acts alone, as well as the measured and calculated values of the 5th harmonic voltage content rate of the low-voltage side power supply bus when the 5th harmonic voltage on the low-voltage side acts alone, are calculated, as shown in Table 3.

[0120] Table 3 Measured and calculated values of the fifth harmonic voltage content of the high and low voltage side power supply bus

[0121] <![CDATA[β H,5 (%)]]> <![CDATA[β′ H,5 (%)]]> <![CDATA[β L,5 (%)]]> <![CDATA[β′ L,5 (%)]]> 1.11 0.1 1.87 0.6

[0122] Assume ε max,1 =ε max,2 =10,ε min,1 =ε min,2 =2, because β H,5 / β′ H,5 =1.11% / 0.1%≈11.1, 11.1>10, so it is determined that the 5th harmonic voltage of the high-voltage side power supply bus is dominated by the background harmonic; because β L,5 / β′ L,5 =1.87% / 0.6%≈3.12, 2<3.12<10, so the 5th harmonic voltage generated by the 5th harmonic voltage of the high-voltage side power supply bus transmitted to the low-voltage side is superimposed on the 5th harmonic voltage of the low-voltage side, and the calculation is but Because 1.1%>0.6%, it is determined that the 5th harmonic voltage of the low-voltage side power supply bus is dominated by background harmonics.

[0123] It should be noted that the logic and / or steps represented in the flowcharts or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing the logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other system that can fetch and execute instructions from an instruction execution system, apparatus, or device), or in conjunction with such instruction execution system, apparatus, or device. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transmit a program for use by an instruction execution system, apparatus, or device, or in conjunction with such instruction execution system, apparatus, or device. More specific examples (non-exhaustive list) of computer-readable media include the following: an electrical connection portion having one or more wires (electronic device), a portable computer disk cartridge (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and programmable read-only memory (EPROM or flash memory), fiber optic devices, and portable compact disc read-only memory (CDROM). Furthermore, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing it in another suitable manner if necessary, and then storing it in a computer memory.

[0124] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application-specific integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0125] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0126] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0127] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for identifying the dominant harmonic sources on the high and low voltage sides of a substation main transformer, characterized in that: include: Collect power quality monitoring data on the high and low voltage sides of the main transformer when the power grid is in operation, including the measured value of the fundamental voltage of the power supply bus, the measured value of the harmonic voltage of the power supply bus at the frequency of concern, and the measured value of the harmonic current of the incoming and outgoing lines at the frequency of concern; Based on the constructed equivalent impedance model and combined with the measured values of the harmonic currents of the incoming and outgoing lines at the frequencies of interest, the calculated values of the harmonic voltages of the power supply bus at the frequencies of interest are obtained; Calculate the measured and calculated values of the harmonic voltage content of the power supply busbars at the frequencies of interest caused by the harmonic currents injected into the system on the high-voltage and low-voltage sides; Compare the measured and calculated values of the harmonic voltage content of the concerned frequencies of the power supply busbars on each side to identify the dominant influencing sources of the harmonic voltage of the power supply busbars on each side.

2. The method for identifying the dominant harmonic sources on the high and low voltage sides of a substation main transformer according to claim 1, characterized in that: The power quality monitoring data collected on the high and low voltage sides of the main transformer under the power grid operation state includes: Based on the measurement points on the high-voltage side and the low-voltage side of the main transformer, the discrete time-domain signals of the voltage and current on each side within the same time period are synchronously sampled; According to the discrete time domain signals of voltage and current on each side, the measured values of fundamental voltage of the power supply bus on each side, the measured values of harmonic voltage at the frequency of interest of the power supply bus and the measured values of harmonic current at the frequency of interest of the incoming and outgoing lines are obtained.

3. The method for identifying the dominant harmonic sources on the high and low voltage sides of a substation main transformer according to claim 2, characterized in that: The measuring points on the high-voltage side include a high-voltage side voltage measuring point and a high-voltage side current measuring point. The high-voltage side voltage measuring point is set on the high-voltage side power supply bus, and the high-voltage side current measuring point is set on the high-voltage side transmission line close to the high-voltage side power supply bus. The current direction is the positive direction of the high-voltage side power supply bus. The measuring points on the low-voltage side include a low-voltage side voltage measuring point and a low-voltage side current measuring point; the low-voltage side voltage measuring point is set on the low-voltage side power supply bus, and the low-voltage side current measuring point is set on the low-voltage side transmission line close to the low-voltage side power supply bus, and the current direction is the positive direction out of the low-voltage side power supply bus.

4. The method for identifying the dominant harmonic sources on the high and low voltage sides of a substation main transformer according to claim 2, characterized in that: The method of obtaining the measured fundamental voltage value of the power supply bus on each side, the measured harmonic voltage value of the power supply bus at the frequency of interest, and the measured harmonic current value of the incoming and outgoing lines at the frequency of interest based on the discrete time domain signals of the voltage on each side and the discrete time domain signals of the current on each side includes: The discrete time domain signals of voltage and current on each side are converted into frequency domain representations, and based on the frequency domain representations, the measured values of the fundamental voltage of the power supply bus on each side, the measured values of the harmonic voltage of the power supply bus at the frequency of interest, and the measured values of the harmonic current of the incoming and outgoing lines at the frequency of interest are obtained.

5. The method for identifying dominant harmonic sources on the high and low voltage sides of a substation main transformer according to claim 1, characterized in that: The equivalent impedance model is constructed based on the short-circuit capacity of the system on each side of the main transformer and the rated voltage on each side. The equivalent harmonic impedance of the system on each side of the equivalent impedance model is: Where S M,H is the short-circuit capacity of the high-voltage side system, S M,L is the short-circuit capacity of the low-voltage side system, U M,H is the rated voltage on the high voltage side, U M,L is the rated voltage of the low voltage side, Z H,h is the hth order equivalent harmonic impedance of the high voltage side system, Z L,h is the hth equivalent harmonic impedance of the low-voltage side system, and h is the harmonic order.

6. The method for identifying the dominant harmonic sources on the high and low voltage sides of a main transformer in a substation according to claim 5, characterized in that: The equivalent impedance model constructed above is combined with the measured values of the harmonic currents of the incoming and outgoing lines at the frequencies of interest to obtain the calculated values of the harmonic voltages of the power supply bus at the frequencies of interest, including: According to the measured RMS value of the hth harmonic current of the incoming and outgoing lines on each side and the equivalent harmonic impedance of the system on each side, the calculated value of the harmonic voltage of the power supply bus at the frequency of interest is obtained, which is expressed as: U′ H,h =I H,h Z H,h U′ L,h =I L,h Z L,h Where U′ H,h is the RMS value of the calculated value of the hth harmonic voltage of the power supply busbar on the high voltage side of the main transformer, I H,h is the root mean square value of the measured value of the hth harmonic current on the high-voltage side of the main transformer, U′ L,h The root mean square value of the calculated value of the hth harmonic voltage of the power supply busbar on the low-voltage side of the main transformer, I L,h It is the RMS value of the measured value of the hth harmonic current on the low-voltage side of the main transformer.

7. The method for identifying dominant harmonic sources on the high and low voltage sides of a substation main transformer according to claim 1, characterized in that: The calculation of the measured and calculated values of the harmonic voltage content rate of the power supply bus at the frequency of interest caused by the harmonic current injected into the system on the high-voltage side and the low-voltage side separately includes: The measured and calculated values of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest when the high-voltage side harmonic voltage acts alone are: Where, β H,h is the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, β′ H,h is the calculated value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, U H,h is the root mean square value of the measured value of the hth harmonic voltage on the high voltage side, U′ H,h is the root mean square value of the calculated value of the hth harmonic voltage on the high voltage side, U H,1 is the RMS value of the measured fundamental voltage on the high-voltage side; When calculating the harmonic voltage on the low-voltage side alone, the measured and calculated values of the harmonic voltage content rate of the low-voltage power supply bus at the frequency of interest are: Where, β L,h is the measured value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, U L,h is the root mean square value of the measured value of the hth harmonic voltage on the low voltage side; U′ L,h is the root mean square value of the calculated value of the hth harmonic voltage on the low voltage side; U L,1 It is the RMS value of the measured fundamental voltage on the low-voltage side.

8. The method for identifying dominant harmonic sources on the high and low voltage sides of a substation main transformer according to claim 1, characterized in that: The comparison of the measured and calculated values of the harmonic voltage content of the concerned frequencies of the power supply busbars on each side and the identification of the dominant influencing sources of the harmonic voltage of the power supply busbars on each side includes: The ratio between the measured value of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest and the calculated value of its voltage content rate is compared with the set first upper limit threshold and first lower limit threshold to identify the dominant influencing source of the harmonic voltage of the high-voltage side power supply bus; The ratio between the measured value of the harmonic voltage content rate of the low-voltage side power supply bus at the frequency of interest and the calculated value of its voltage content rate is compared with the set second upper limit threshold and second lower limit threshold to identify the dominant influencing source of the harmonic voltage of the low-voltage side power supply bus.

9. The method for identifying the dominant harmonic sources on the high and low voltage sides of a main transformer in a substation according to claim 8, characterized in that: The method of comparing the ratio between the measured value of the harmonic voltage content rate of the high-voltage side power supply bus at the frequency of interest and the calculated value of the voltage content rate thereof with the set first upper limit threshold and first lower limit threshold to identify the dominant influencing source of the harmonic voltage of the high-voltage side power supply bus includes: when When , it is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by the background harmonic; when When , it is determined that the hth harmonic voltage of the power supply busbar on the high voltage side is dominated by the harmonic current of the nonlinear load on the low voltage side; when When, if It is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by background harmonics; if It is determined that the hth harmonic voltage of the high-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load; if It is determined that the hth harmonic voltage of the power supply bus on the high-voltage side is dominated by the background harmonic and the harmonic current of the nonlinear load on the low-voltage side; Among them, β H,h is the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, β′ H,h is the calculated value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, for and β H,h The phase difference, θ is β H,h and β′ L,h The phase difference, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, ε max,1 is the first upper threshold, ε min,1 is the first lower threshold.

10. The method for identifying dominant harmonic sources on the high and low voltage sides of a substation main transformer according to claim 8, characterized in that: The method of comparing the ratio between the measured value of the harmonic voltage content rate of the low-voltage side power supply bus at the frequency of interest and the calculated value of the voltage content rate thereof with the set second upper threshold and second lower threshold to identify the dominant influencing source of the harmonic voltage of the low-voltage side power supply bus includes: when When , it is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by background harmonics; when When , it is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load; when When, if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by background harmonics; if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the harmonic current of the low-voltage side nonlinear load; if It is determined that the hth harmonic voltage of the low-voltage side power supply bus is dominated by the background harmonic and the low-voltage side nonlinear load harmonic current; Among them, β L,h is the measured value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, β′ L,h is the calculated value of the hth harmonic voltage content rate of the low-voltage side power supply bus when the hth harmonic voltage on the low-voltage side acts alone, for and β H,h The phase difference, θ is β H,h and β′ L,h The phase difference, β H,h is the measured value of the hth harmonic voltage content rate of the high-voltage side power supply bus when the hth harmonic voltage on the high-voltage side acts alone, ε max,2 is the second upper threshold, ε min,2 is the second lower threshold.

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