Method and system for judging measurement accuracy of harmonic voltage at high and medium voltage sides of main transformer of transformer substation

Abstract

The invention discloses a transformer station main transformer high and medium voltage side harmonic voltage measurement accuracy determination method and system. The method comprises the following steps: synchronously collecting transformer station main transformer high, medium and low voltage side power supply bus harmonic voltage phasors and outgoing line harmonic current phasors in the same time; establishing high, medium and low voltage side equivalent impedance models of the main transformer according to specification parameters of the main transformer; calculating a neutral point harmonic voltage of the main transformer equivalent impedance model; calculating the harmonic voltage of the medium-voltage side of the main transformer, comparing the harmonic voltage with the actually measured harmonic voltage of the medium-voltage side of the main transformer, distinguishing the measurement accuracy of the harmonic voltage of the medium-voltage side of the main transformer, calculating the harmonic voltage of the high-voltage side of the main transformer, and comparing the harmonic voltage with the actually measured harmonic voltage of the high-voltage side of the main transformer; and the main transformer high-voltage side harmonic voltage measurement accuracy is distinguished. The method solves the technical problem of judging whether harmonic voltage measurement distortion exists on the high-voltage side and the medium-voltage side of the main transformer of the transformer substation or not.

Description

Technical Field

[0001] The present invention relates to the technical field of harmonic voltage measurement, and specifically to a method for discriminating the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer in a substation. Background Art

[0002] With the large-scale application of various power electronic devices and non-linear and impulse loads, the harmonic problem in the new power system has become increasingly prominent. Accurately obtaining harmonic measurement data is a prerequisite for carrying out harmonic analysis, evaluation and control. Currently, in grid substations, electromagnetic current transformers are widely used for current measurement, and there is basically no measurement distortion for harmonic currents below 1000 Hz. For the voltage measurement of 10 / 35 kV busbars, most use electromagnetic voltage transformers (Potential Transformers, PTs), which have high measurement accuracy and can provide accurate voltage measurement data. While for power systems of 110 kV and above, the main sensing terminals for voltage measurement are capacitor voltage transformers (Capacitor Voltage Transformers, CVTs). The equivalent impedance of the stray capacitance of the compensation reactor and the primary winding of the intermediate transformer in the CVT changes with frequency, and there are resonance problems in some specific scenarios, resulting in harmonic voltage measurement distortion and easily misleading the implementation of work such as harmonic tracing and control. For example, at the power frequency of 50 Hz, series resonance occurs between the voltage-dividing capacitor and the compensation reactor in the CVT. Under non-power frequency conditions, the reactor cannot fully compensate or under-compensate the capacitor voltage divider, resulting in voltage distortion and the destruction of the resonance state. The transformation ratio of the capacitor voltage transformer will change with the frequency.

[0003] The invention patent with the publication number of CN112305484A discloses a method and device for discriminating the accuracy of harmonic measurement of a capacitor voltage transformer, which mainly identifies the accuracy of harmonic phase measurement of the high-voltage side capacitor voltage transformer. However, it cannot simultaneously identify the accuracy of harmonic amplitude measurement of the high- and medium-voltage side capacitor voltage transformers.

[0004] The invention patent with the publication number of CN10365445A discloses a method for high-voltage harmonic measurement using a capacitor voltage transformer, which mainly modifies the high-voltage side conventional capacitor voltage transformer and the low-voltage side electromagnetic unit branch, rather than identifying the accuracy based on the original measurement data. And it cannot simultaneously identify the accuracy of harmonic measurement of the original high- and medium-voltage side capacitor voltage transformers.

[0005] The invention patent with the publication number of CN117517825A discloses a real-time monitoring method for the medium voltage side of a distribution transformer based on digital twin technology. This patent uses the voltage and current on the low voltage side and the resistance and inductance of the distribution transformer, and uses the methods of differentiation and integration to calculate the voltage and current on the medium voltage side. However, the monitoring object of this patent is the voltage and current on the medium voltage side of the transformer, rather than the harmonic voltage. At the same time, the accuracy of harmonic measurement is not identified.

[0006] Therefore, how to utilize the harmonic current monitoring data and the harmonic voltage monitoring data on the low voltage side of the main transformer, and combine the substation system parameters to effectively judge the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer is a key technical problem that urgently needs to be solved at present. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: to propose a method for judging the accuracy of harmonic voltage measurement on the high and medium voltage sides of a substation main transformer, comprehensively utilizing the harmonic current data of each outgoing line of the main transformer, the harmonic voltage data on the low voltage side of the main transformer, and the system electrical parameters, and solving the technical problem of simultaneously judging whether there is harmonic voltage measurement distortion on the high and medium voltage sides of the substation main transformer.

[0008] To solve the above technical problems, the present invention provides the following technical solutions: A method for judging the accuracy of harmonic voltage measurement on the high and medium voltage sides of a substation main transformer, including: Synchronously collect the harmonic voltage phasors of the power supply buses on the high, medium, and low voltage sides of the substation main transformer and the harmonic current phasors of each outgoing line at the same time; Establish an equivalent impedance model for the high, medium, and low voltage sides of the main transformer according to the specification parameters of the main transformer; Based on the harmonic voltage phasor and harmonic current phasor on the low voltage side, calculate the harmonic voltage of the neutral point of the equivalent impedance model of the main transformer; According to the collected harmonic current phasor on the medium voltage side, and based on the harmonic voltage of the neutral point, calculate the harmonic voltage on the medium voltage side of the main transformer, and compare it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the medium voltage side to distinguish the accuracy of harmonic voltage measurement on the medium voltage side of the main transformer; According to the collected harmonic current phasor on the high voltage side, and based on the harmonic voltage of the neutral point, calculate the harmonic voltage on the high voltage side of the main transformer, and compare it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the high voltage side to distinguish the accuracy of harmonic voltage measurement on the high voltage side of the main transformer.

[0009] Technical effect: Based on the data-model joint-driven method, on the one hand, the harmonic monitoring data is fully utilized, and the accurate harmonic current data of the high, medium, and low voltage sides of the main transformer and the harmonic voltage data of the low voltage side are used as data-driven; on the other hand, the mechanism model is simple and clear. The equivalent impedance model of the main transformer is constructed using the system topology and grid parameters and used as the model-driven. Finally, the harmonic voltages of the high and medium voltage sides of the main transformer are jointly calculated and compared with the measured harmonic voltages of the high and medium voltage sides of the main transformer, thereby identifying the accuracy of the harmonic voltage measurement of the high and medium voltage sides of the main transformer, verifying the accuracy of the harmonic data of the high and medium voltage sides of the main transformer, effectively improving the harmonic measurement accuracy of the high and medium voltage sides of the main transformer, and providing reliable data support for the subsequent harmonic abnormal state analysis of the power grid across voltage levels.

[0010] In an embodiment of the present invention, according to the specification parameters of the main transformer, an equivalent impedance model of the high, medium, and low voltage sides of the main transformer is established, including: establishing an equivalent impedance model of the high, medium, and low voltage sides of the main transformer according to the rated capacity, capacity percentage, connection method, maximum short-circuit loss, rated voltage of the high voltage side, short-circuit voltage between the high and medium voltage windings, short-circuit voltage between the medium and low voltage windings, and short-circuit voltage between the low and high voltage windings of the main transformer.

[0011] In an embodiment of the present invention, the expression of the equivalent impedance model of the high, medium, and low voltage sides of the main transformer is: ; ; ; where ; ; ; ; ; ; In the formula, , , are the sub-harmonic impedances of the high, medium, and low voltage windings of the main transformer equivalent to the high voltage side respectively; , , are the resistances of the high, medium, and low voltage windings of the main transformer equivalent to the high voltage side respectively; , , The reactances of the high-voltage side, medium-voltage side, and low-voltage side windings of the main transformer, respectively, equivalent to the high-voltage side; is the harmonic order; is the imaginary unit; is the short-circuit voltage between the high- and medium-voltage side windings; is the short-circuit voltage between the medium- and low-voltage side windings; is the short-circuit voltage between the low- and high-voltage side windings; is the rated voltage of the high-voltage side; is the rated capacity of the main transformer; is the resistance of the main transformer winding at 100% capacity, equivalent to the high-voltage side; is the resistance of the main transformer winding at 50% capacity, equivalent to the high-voltage side.

[0012] In an embodiment of the present invention, calculating the neutral harmonic voltage of the main transformer equivalent impedance model includes: According to the collected th harmonic voltage phasor, harmonic current phasor of the low-voltage side of the main transformer, and the th harmonic impedance of the low-voltage side winding of the main transformer equivalent impedance model, equivalent to the high-voltage side, and combining the connection mode of the main transformer, obtain the th harmonic voltage phasor of the neutral point, equivalent to the high-voltage side, as the neutral harmonic voltage.

[0013] In an embodiment of the present invention, the expression of the neutral harmonic voltage of the main transformer equivalent impedance model is: ; In the formula, is the th harmonic voltage phasor of the neutral point of the main transformer, equivalent to the high-voltage side; is the th harmonic voltage phasor of the low-voltage side of the main transformer; is the th harmonic current phasor of the low-voltage side of the main transformer; is the th harmonic impedance of the low-voltage side winding of the main transformer, equivalent to the high-voltage side; is the turns ratio between the high- and low-voltage sides; is the angle; is the harmonic order; is a natural number.

[0014] In an embodiment of the present invention, distinguishing the measurement accuracy of the harmonic voltage of the medium-voltage side of the main transformer includes: Calculating the difference rate between the harmonic voltage of the medium-voltage side of the main transformer and the effective voltage value corresponding to the actually measured harmonic voltage phasor of the medium-voltage side, and taking it as the harmonic voltage difference rate of the medium-voltage side ; Compare the harmonic voltage difference rate on the medium-voltage side with the harmonic threshold on the medium-voltage side . If , the measurement of the harmonic voltage on the medium-voltage side of the main transformer is accurate; if , the measurement of the harmonic voltage on the medium-voltage side of the main transformer is inaccurate.

[0015] In an embodiment of the present invention, the harmonic voltage on the medium-voltage side of the main transformer is obtained through the following formula: ; ; In the formula, is the theoretical value of the phasor of the th harmonic voltage on the medium-voltage side of the main transformer; is the th harmonic voltage on the medium-voltage side of the main transformer; is the theoretical value of the real part of the phasor of the th harmonic voltage on the medium-voltage side of the main transformer; is the theoretical value of the imaginary part of the phasor of the th harmonic voltage on the medium-voltage side of the main transformer; is the phasor of the th harmonic voltage of the neutral point of the main transformer equivalent to the high-voltage side; is the phasor of the th harmonic current on the medium-voltage side of the main transformer; is the th harmonic impedance of the medium-voltage side winding of the main transformer equivalent to the high-voltage side; is the transformation ratio between the high-voltage and medium-voltage sides; is the harmonic order; is the imaginary unit.

[0016] In an embodiment of the present invention, identifying the accuracy of the harmonic voltage measurement on the high-voltage side of the main transformer includes: Calculate the difference rate between the harmonic voltage on the high-voltage side of the main transformer and the effective voltage value corresponding to the phasor of the actually measured harmonic voltage on the high-voltage side, and use it as the harmonic voltage difference rate on the high-voltage side ; Compare the harmonic voltage difference rate on the high-voltage side with the harmonic threshold on the high-voltage side . If , the measurement of the harmonic voltage on the high-voltage side of the main transformer is accurate; if , the measurement of the harmonic voltage on the high-voltage side of the main transformer is inaccurate.

[0017] In an embodiment of the present invention, the harmonic voltage on the high-voltage side of the main transformer is obtained through the following formula: ; ; In the formula, is the theoretical value of the phasor of the th harmonic voltage on the high-voltage side of the main transformer; is the th harmonic voltage on the high-voltage side of the main transformer; is the theoretical value of the real part of the phasor of the th harmonic voltage on the high-voltage side of the main transformer; is the theoretical value of the imaginary part of the phasor of the th harmonic voltage on the high-voltage side of the main transformer; is the phasor of the th harmonic voltage equivalent from the neutral point of the main transformer to the high-voltage side; is the phasor of the th harmonic current on the high-voltage side of the main transformer; is the th harmonic impedance equivalent from the winding on the high-voltage side of the main transformer to the high-voltage side; is the harmonic order; is the imaginary unit.

[0018] The present invention also provides a discrimination system for the measurement accuracy of harmonic voltage on the high- and medium-voltage sides of the main transformer in a substation, which applies the above-mentioned discrimination method for the measurement accuracy of harmonic voltage on the high- and medium-voltage sides of the main transformer in a substation, and includes: A data acquisition module, which is used to synchronously collect the phasors of harmonic voltages on the power supply buses of the high-, medium- and low-voltage sides of the main transformer in the substation and the phasors of harmonic currents of each outgoing line at the same time; An impedance modeling module, which is used to establish equivalent impedance models for the high-, medium- and low-voltage sides of the main transformer according to the specification parameters of the main transformer; A neutral point module, which is used to calculate the harmonic voltage of the neutral point of the equivalent impedance model of the main transformer based on the phasors of harmonic voltages and harmonic currents on the low-voltage side; A medium-voltage side discrimination module, which is used to calculate the harmonic voltage of the medium-voltage side of the main transformer according to the collected phasor of the harmonic current on the medium-voltage side and based on the harmonic voltage of the neutral point, and compare it with the effective voltage value corresponding to the actually measured phasor of the harmonic voltage on the medium-voltage side to discriminate the measurement accuracy of the harmonic voltage on the medium-voltage side of the main transformer; A high-voltage side discrimination module, which is used to calculate the harmonic voltage of the high-voltage side of the main transformer according to the collected phasor of the harmonic current on the high-voltage side and based on the harmonic voltage of the neutral point, and compare it with the effective voltage value corresponding to the actually measured phasor of the harmonic voltage on the high-voltage side to discriminate the measurement accuracy of the harmonic voltage on the high-voltage side of the main transformer.

[0019] Compared with the prior art, the beneficial effects of the present invention are: The present invention does not require modification of the harmonic monitoring device. It directly and effectively identifies the data measurement accuracy of the harmonic voltage amplitude and phase in the high-voltage power grid based on the harmonic monitoring data provided by the power grid company, provides further guarantee for the reliability of using CVT to measure harmonic voltage data, and avoids misjudgment of harmonic tracing analysis caused by distorted harmonic voltage monitoring data.

[0020] In the prior art, it is only possible to distinguish the accuracy of harmonic voltage measurement on a single side, while the present invention can jointly calculate the harmonic voltages on the high-voltage and medium-voltage sides of the main transformer to distinguish the accuracy of harmonic voltage measurement on the high-voltage and medium-voltage sides of the main transformer. Brief Description of the Drawings

[0021] Figure 1 It is a flowchart of a method for discriminating the accuracy of harmonic voltage measurement on the high-voltage and medium-voltage sides of the main transformer of a substation according to an embodiment of the present invention.

[0022] Figure 2 It is a schematic diagram of the positions of harmonic voltage and harmonic current sampling points according to an embodiment of the present invention.

[0023] Figure 3 It is a schematic diagram of the equivalent impedance models on the high-voltage, medium-voltage, and low-voltage sides of the main transformer according to an embodiment of the present invention.

[0024] Figure 4 It is a measurement diagram of the effective values of the 5th harmonic voltage and current on the power supply bus of the high-voltage side of the main transformer of a substation according to an embodiment of the present invention.

[0025] Figure 5 It is a measurement diagram of the effective values of the 5th harmonic voltage and current on the power supply bus of the medium-voltage side of the main transformer of a substation according to an embodiment of the present invention.

[0026] Figure 6 It is a measurement diagram of the effective values of the 5th harmonic voltage and current on the power supply bus of the low-voltage side of the main transformer of a substation according to an embodiment of the present invention.

[0027] Figure 7 It is a block diagram of a system for discriminating the accuracy of harmonic voltage measurement on the high-voltage and medium-voltage sides of the main transformer of a substation according to an embodiment of the present invention. Detailed Embodiments

[0028] To facilitate the understanding of the technical solution of the present invention by those skilled in the art, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings of the specification.

[0029] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality" means two or more, unless otherwise specifically defined.

[0030] Please refer to Figure 1 shown below. This embodiment provides a method for discriminating the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer in a substation, including: S10. Synchronously collect the harmonic voltage phasors of the power supply buses on the high, medium, and low voltage sides of the main transformer in the substation and the harmonic current phasors of each outgoing line at the same time.

[0031] Please refer to Figure 2 shown below. In this embodiment, the voltage time-domain discrete signals , , and the current time-domain discrete signals , , are synchronously sampled at the voltage measurement points 1, 2, 3 and the current measurement points 1, 2, 3 within the same time period. The current direction is as shown in Figure 3 . Among them, is the number of the time-domain discrete signals of the sampled voltage and current waveforms. 1, 2, and 3 respectively represent the high, medium, and low voltage sides of the main transformer. It is known that the current measurement results on the high, medium, and low voltage sides of the main transformer are accurate; the voltage on the low voltage side of the main transformer is measured by a PT, and the result is accurate. The voltages on the high and medium voltage sides of the main transformer are measured by a CVT, and the accuracy of the result cannot be determined. The sampled signals are converted from the time-domain representation to the frequency-domain representation through the discrete Fourier transform. The window width is set to 10 cycles, and the specific calculation formula is as follows: ; ; ; ; In the formula, is the harmonic voltage phasor at the th harmonic at the voltage measurement point ; is the real part of the harmonic voltage phasor at the th harmonic at the voltage measurement point ; is the imaginary part of the harmonic voltage phasor at the th harmonic at the voltage measurement point ; is the harmonic current phasor at the th harmonic at the current measurement point ; is the real part of the harmonic current phasor at the th harmonic at the current measurement point ; is the imaginary part of the harmonic current phasor at the th harmonic at the current measurement point ; is the voltage and current measurement point, = 1, 2, 3 respectively represent the high, medium, and low voltage sides of the main transformer; is the voltage measurement point at the effective value of the nth harmonic voltage; is the voltage measurement point at the effective value of the nth harmonic current; is the harmonic order; is the number of sampling points for 10 cycles of the time-domain discrete signal of the voltage or current waveform; is the number of the time-domain discrete signal, and the value range is ; is the imaginary unit; is the natural constant.

[0032] In this embodiment, considering the effectiveness of harmonic voltage and current data acquisition, the voltage difference threshold and the current difference threshold are respectively set. It is required that and , and the filtered and are retained, where is the mean value of , is the mean value of . It is recommended to set it to or and other equivalent values. It is recommended to set it to or and other equivalent values, which is beneficial to the effectiveness of harmonic voltage and current data acquisition. Because the collected harmonic voltage and current data may have abnormal data due to reasons such as changes in the grid operation state, the recommended deviations of 5% and 10% are set based on engineering experience, and the effectiveness of the collected harmonic voltage and current data is relatively high under this setting.

[0033] S20. According to the specification parameters of the main transformer, establish the equivalent impedance models of the high, medium, and low voltage sides of the main transformer.

[0034] Please refer to Figure 3 as shown. In this embodiment, obtain the rated capacity of the main transformer, the capacity percentage, the connection mode is Y - Y - △, the maximum short-circuit loss , the rated voltage of the high voltage side , the transformation ratio between the high and medium voltage sides , the transformation ratio between the high and low voltage sides , the short-circuit voltage between the high and medium voltage windings , the short-circuit voltage between the medium and low voltage windings , the short-circuit voltage between the low and high voltage windings . Establish the equivalent impedance models for the high, medium, and low voltage sides of the main transformer.

[0035] In this embodiment, the capacity percentages are divided into three categories, namely 100% / 100% / 100%, 100% / 100% / 50%, and 100% / 50% / 100%. The resistances of the main transformer windings corresponding to different capacities equivalent to the high voltage side are as follows: ; ; In the formula, is the resistance of the main transformer winding with 100% capacity equivalent to the high voltage side; is the resistance of the main transformer winding with 50% capacity equivalent to the high voltage side.

[0036] In this embodiment, the types of capacity percentages are described as follows: For example, for a three-winding transformer with a rated capacity of 750 MVA and a capacity percentage of 100% / 100% / 100%, the rated capacities of the high, medium, and low voltage sides of the three-winding transformer are 750 MVA, 750 MVA, and 750 MVA respectively. For example, for a three-winding transformer with a rated capacity of 500 MVA and a capacity percentage of 100% / 100% / 50%, the rated capacities of the high, medium, and low voltage sides of the three-winding transformer are 500 MVA, 500 MVA, and 250 MVA respectively.

[0037] In this embodiment, the resistances of each winding of the main transformer equivalent to the high voltage side are as follows: ; ; ; In the formula, is the resistance of the high voltage side winding of the main transformer equivalent to the high voltage side; is the resistance of the medium voltage side winding of the main transformer equivalent to the high voltage side; is the resistance of the low voltage side winding of the main transformer equivalent to the high voltage side.

[0038] In this embodiment, the reactances of each winding of the main transformer equivalent to the high voltage side are as follows: ; ; ; In the formula, is the reactance of the high voltage side winding of the main transformer equivalent to the high voltage side; is the reactance of the medium voltage side winding of the main transformer equivalent to the high voltage side; is the reactance of the low voltage side winding of the main transformer equivalent to the high voltage side.

[0039] In this embodiment, the calculation formula for the harmonic impedance of each winding of the main transformer equivalent to the high-voltage side, that is, the expression of the equivalent impedance model of the high, medium, and low voltage sides of the main transformer is: ; ; ; In the formula, is the th harmonic impedance of the high-voltage side winding of the main transformer equivalent to the high-voltage side; is the th harmonic impedance of the medium-voltage side winding of the main transformer equivalent to the high-voltage side; is the th harmonic impedance of the low-voltage side winding of the main transformer equivalent to the high-voltage side.

[0040] S30. Based on the harmonic voltage phasor and harmonic current phasor of the low-voltage side, calculate the harmonic voltage of the neutral point of the equivalent impedance model of the main transformer.

[0041] In an embodiment of the present invention, according to the th harmonic voltage phasor , current phasor collected from the low-voltage side of the main transformer, the th harmonic impedance of the low-voltage side winding of the main transformer equivalent to the high-voltage side that has been obtained, and the main transformer connection mode Y-Y-Δ, find the th harmonic voltage of the neutral point equivalent to the high-voltage side. The calculation formula is as follows: ; In the formula, is the th harmonic voltage phasor of the neutral point of the main transformer equivalent to the high-voltage side; is the th harmonic voltage phasor of the low-voltage side of the main transformer; is the th harmonic current phasor of the low-voltage side of the main transformer; is the th harmonic impedance of the low-voltage side winding of the main transformer equivalent to the high-voltage side; is the turns ratio between the high and low voltage sides; is the angle, and the specific value is related to the connection group. In particular, when the connection group is Yd11, = 30°; is a natural number.

[0042] S40, according to the collected harmonic current phasor on the medium voltage side and based on the neutral point harmonic voltage, calculate the harmonic voltage on the medium voltage side of the main transformer, and compare it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the medium voltage side to identify the measurement accuracy of the harmonic voltage on the medium voltage side of the main transformer.

[0043] In one embodiment of the present invention, according to the collected data on the medium voltage side of the main transformer Subharmonic current phasors , the neutral point of the main transformer is equivalent to the high voltage side Subharmonic voltage , the obtained main transformer medium voltage side winding is equivalent to the high voltage side Subharmonic impedance , find the medium voltage side of the main transformer Subharmonic voltage phasor theoretical value , the calculation formula is as follows: ; ; In the formula, For the medium voltage side of the main transformer Theoretical value of subharmonic voltage phasor; For the medium voltage side of the main transformer Theoretical value of the effective value of subharmonic voltage, that is, the medium voltage side of the main transformer Subharmonic voltage; For the medium voltage side of the main transformer Theoretical value of the real part of subharmonic voltage phasor; For the medium voltage side of the main transformer Theoretical value of the imaginary part of subharmonic voltage phasor; The neutral point of the main transformer is equivalent to the high voltage side Subharmonic voltage phasors; For the medium voltage side of the main transformer Subharmonic current phasors; The medium voltage winding of the main transformer is equivalent to the high voltage winding Subharmonic impedance; is the transformation ratio of high and medium voltage sides.

[0044] calculate and The difference change is as follows: ; In the formula, For the medium voltage side of the main transformer The change rate of the difference between the measured value and the theoretical value of the subharmonic voltage effective value, that is, the harmonic voltage difference rate on the medium voltage side, The actual measurement of the medium voltage side of the main transformer The effective value of subharmonic voltage.

[0045] If , the harmonic voltage measurement of the medium voltage side of the main transformer is accurate; if , the harmonic voltage measurement of the medium voltage side of the main transformer is inaccurate. Among them, is the threshold of the change rate of the difference between the measured value and the theoretical value of the root mean square value of the th harmonic voltage on the medium voltage side of the main transformer, that is, the harmonic threshold on the high voltage side. It is recommended to take values such as 5% and 10%.

[0046] S50. According to the collected harmonic current phasor on the high voltage side and based on the harmonic voltage at the neutral point, calculate the harmonic voltage on the high voltage side of the main transformer, and compare it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the high voltage side to identify the accuracy of the harmonic voltage measurement on the high voltage side of the main transformer.

[0047] In an embodiment of the present invention, according to the collected th harmonic current phasor on the high voltage side of the main transformer, the th harmonic voltage equivalent from the neutral point of the main transformer to the high voltage side, and the th harmonic impedance equivalent from the high voltage side of the main transformer to the high voltage side, calculate the theoretical value of the th harmonic voltage phasor on the high voltage side of the main transformer. The calculation formula is as follows: ; ; In the formula, is the theoretical value of the th harmonic voltage phasor on the high voltage side of the main transformer; is the theoretical value of the effective value of the th harmonic voltage on the high voltage side of the main transformer, that is, the th harmonic voltage on the high voltage side of the main transformer; is the real part theoretical value of the th harmonic voltage phasor on the high voltage side of the main transformer; is the imaginary part theoretical value of the th harmonic voltage phasor on the high voltage side of the main transformer; is the th harmonic voltage phasor equivalent from the neutral point of the main transformer to the high voltage side; is the th harmonic current phasor on the high voltage side of the main transformer; is the th harmonic impedance equivalent from the winding of the high voltage side of the main transformer to the high voltage side.

[0048] Calculate and The variation of the difference is as follows: ; In the formula, is the variation rate of the difference between the measured value and the theoretical value of the effective value of the th harmonic voltage on the high-voltage side of the main transformer, that is, the harmonic voltage difference rate on the high-voltage side; is the effective value of the th harmonic voltage actually measured on the high-voltage side of the main transformer.

[0049] If , the harmonic voltage measurement on the high-voltage side of the main transformer is accurate; if , the harmonic voltage measurement on the high-voltage side of the main transformer is inaccurate. Among them, is the threshold value of the variation rate of the difference between the measured value and the theoretical value of the root mean square value of the th harmonic voltage on the high-voltage side of the main transformer set, that is, the harmonic threshold on the high-voltage side. It is recommended to take values such as 5% and 10%.

[0050] In an embodiment of the present invention, undoubtedly, the order of steps S40 and S50 can be interchanged.

[0051] To better introduce the present invention, the following is a detailed description through a specific embodiment: A certain 220 kV substation is as Figure 2 shown. At voltage measurement points 1, 2, 3 and current measurement points 1, 2, 3, the 5th harmonic voltage phasors of the power supply buses on the high, medium and low voltage sides of the main transformer of the substation and the 5th harmonic current phasors of each outgoing line are synchronously collected at the same time. Let be , be . According to and , retain the filtered and . Their effective value diagrams are as Figure 4 , Figure 5 , Figure 6 shown.

[0052] Obtain the rated capacity = 180 MVA of the main transformer. The capacity percentage is 100% / 100% / 50%, the connection method is YNyn0d11, the maximum short-circuit loss = 100 kW, the rated voltage of the high-voltage side = 230 kV, the turns ratio of the high and medium voltage sides = 230 / 121, the turns ratio of the high and low voltage sides = 230 / 10.5, the short-circuit voltage between the high and medium voltage windings = 13.78%, the short - circuit voltage between the medium - voltage and low - voltage windings = 7.55%, the short - circuit voltage between the low - voltage and high - voltage windings = 23.80%. Establish the equivalent impedance models of the high - voltage, medium - voltage, and low - voltage sides of the main transformer as Figure 3 shown. Calculate the 5th - harmonic impedance of each winding of the high - voltage, medium - voltage, and low - voltage sides of the main transformer equivalent to the high - voltage side as shown in Table 1.

[0053] Table 1 The 5th - harmonic impedance of each winding of the high - voltage, medium - voltage, and low - voltage sides of the main substation equivalent to the high - voltage side

[0054] Calculate the theoretical values of the effective values of the 5th - harmonic voltages on the high - voltage and medium - voltage sides of the main transformer 、 , and compare them with the measured values of the effective values of the 5th - harmonic voltages on the high - voltage and medium - voltage sides of the main transformer 、 Calculate the difference change rate, and the results are shown in Table 2.

[0055] Table 2 Comparison of the theoretical values and measured values of the effective values of the 5th - harmonic voltages on the high - voltage and medium - voltage sides of the main substation

[0056] Let be 5%, be 5%. Therefore, the difference change rate between the theoretical value of the effective value of the 5th - harmonic voltage on the high - voltage side of the main transformer and the measured value , then the measurement of the harmonic voltage on the high - voltage side of the main transformer is accurate. The difference change rate between the theoretical value of the effective value of the 5th - harmonic voltage on the medium - voltage side of the main transformer and the measured value , then the measurement of the harmonic voltage on the medium - voltage side of the main transformer is accurate.

[0057] Please refer to Figures 1 to 7 shown. In another embodiment of the present invention, a discrimination system for the measurement accuracy of the harmonic voltages on the high - voltage, medium - voltage, and low - voltage sides of the main transformer in a substation is also provided. Applying the above - mentioned discrimination method for the measurement accuracy of the harmonic voltages on the high - voltage, medium - voltage, and low - voltage sides of the main transformer in a substation, it includes: A data acquisition module, used to synchronously collect the harmonic voltage phasors of the power - supply buses on the high - voltage, medium - voltage, and low - voltage sides of the main transformer in the substation and the harmonic current phasors of each outgoing line at the same time.

[0058] An impedance modeling module, used to establish the equivalent impedance models of the high - voltage, medium - voltage, and low - voltage sides of the main transformer according to the specification parameters of the main transformer.

[0059] The neutral point module is used to calculate the harmonic voltage at the neutral point of the equivalent impedance model of the main transformer based on the harmonic voltage phasor and harmonic current phasor on the low-voltage side.

[0060] The medium-voltage side discrimination module is used to calculate the harmonic voltage on the medium-voltage side of the main transformer according to the collected harmonic current phasor on the medium-voltage side and based on the harmonic voltage at the neutral point, and compare it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the medium-voltage side to discriminate the measurement accuracy of the harmonic voltage on the medium-voltage side of the main transformer.

[0061] The high-voltage side discrimination module is used to calculate the harmonic voltage on the high-voltage side of the main transformer according to the collected harmonic current phasor on the high-voltage side and based on the harmonic voltage at the neutral point, and compare it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the high-voltage side to discriminate the measurement accuracy of the harmonic voltage on the high-voltage side of the main transformer.

[0062] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention, and any reference signs in the claims should not be regarded as limiting the claims involved.

[0063] The above-described embodiments only represent the implementation manners of the invention. The protection scope of the present invention is not limited to the above embodiments. For those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all belong to the protection scope of the present invention.

Claims

1. A discrimination method for the measurement accuracy of harmonic voltage on the high and medium voltage sides of the main transformer in a substation, characterized in that, Including: Synchronously collect the harmonic voltage phasors of the power supply buses on the high, medium, and low voltage sides of the main transformer in a substation and the harmonic current phasors of each outgoing line at the same time; Establish equivalent impedance models for the high, medium, and low voltage sides of the main transformer according to the specification parameters of the main transformer; Based on the harmonic voltage phasor and harmonic current phasor on the low voltage side, calculate the harmonic voltage at the neutral point of the equivalent impedance model of the main transformer; According to the collected harmonic current phasor on the medium voltage side and based on the harmonic voltage at the neutral point, calculate the harmonic voltage on the medium voltage side of the main transformer, and compare it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the medium voltage side to identify the measurement accuracy of the harmonic voltage on the medium voltage side of the main transformer; According to the collected harmonic current phasor on the high voltage side and based on the harmonic voltage at the neutral point, calculate the harmonic voltage on the high voltage side of the main transformer, and compare it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the high voltage side to identify the measurement accuracy of the harmonic voltage on the high voltage side of the main transformer.

2. The discrimination method for the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer in a substation according to claim 1, characterized in that, Establish equivalent impedance models for the high, medium, and low voltage sides of the main transformer according to the specification parameters of the main transformer, including: establish equivalent impedance models for the high, medium, and low voltage sides of the main transformer according to the rated capacity, capacity percentage, connection method, maximum short-circuit loss, rated voltage on the high voltage side, short-circuit voltage between the high and medium voltage windings, short-circuit voltage between the medium and low voltage windings, and short-circuit voltage between the low and high voltage windings of the main transformer.

3. The discrimination method for the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer in a substation according to claim 2, characterized in that, The expressions for the equivalent impedance models of the high, medium, and low voltage sides of the main transformer are: ； ； ； Where, ； ； ； ； ； ； Wherein, , , are respectively the sub - harmonic impedances of the high - voltage side, medium - voltage side, and low - voltage side windings of the main transformer, equivalent to the high - voltage side; , , are respectively the resistances of the high - voltage side, medium - voltage side, and low - voltage side windings of the main transformer, equivalent to the high - voltage side; , , are respectively the reactances of the high - voltage side, medium - voltage side, and low - voltage side windings of the main transformer, equivalent to the high - voltage side; is the harmonic order; is the imaginary unit; is the short - circuit voltage between the high - voltage and medium - voltage side windings; is the short - circuit voltage between the medium - voltage and low - voltage side windings; is the short - circuit voltage between the low - voltage and high - voltage side windings; is the rated voltage of the high - voltage side; is the rated capacity of the main transformer; is the resistance of the main transformer winding equivalent to the high - voltage side at 100% capacity; is the resistance of the main transformer winding equivalent to the high - voltage side at 50% capacity.

4. The method for discriminating the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer in a substation according to claim 1, characterized in that, Calculating the harmonic voltage at the neutral point of the equivalent impedance model of the main transformer includes: According to the collected sub-harmonic voltage phasor, harmonic current phasor on the low-voltage side of the main transformer, and the sub-harmonic impedance of the low-voltage winding in the equivalent impedance model of the main transformer referred to the high-voltage side, combined with the connection mode of the main transformer, the sub-harmonic voltage phasor of the neutral point referred to the high-voltage side is obtained as the harmonic voltage of the neutral point. ​ 5. The discrimination method for the measurement accuracy of harmonic voltage on the high and medium voltage sides of the main transformer in a substation according to claim 4, characterized in that, The expression for the harmonic voltage at the neutral point of the equivalent impedance model of the main transformer is: ； In the formula, is the sub-harmonic voltage phasor equivalent to the neutral point of the main transformer on the high-voltage side; is the sub-harmonic voltage phasor on the low-voltage side of the main transformer; is the sub-harmonic current phasor on the low-voltage side of the main transformer; is the sub-harmonic impedance equivalent to the low-voltage side winding of the main transformer on the high-voltage side; is the turns ratio between the high-voltage side and the low-voltage side; is the angle; is the harmonic order; is a natural number.

6. The method for discriminating the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer in a substation according to claim 1, characterized in that Identifying the measurement accuracy of the harmonic voltage on the medium voltage side of the main transformer includes: Calculate the difference rate between the effective voltage value corresponding to the harmonic voltage on the medium-voltage side of the main transformer and the phasor of the actually measured harmonic voltage on the medium-voltage side, and use it as the harmonic voltage difference rate on the medium-voltage side ; Compare the harmonic voltage difference rate on the medium-voltage side with the harmonic threshold on the medium-voltage side . If , the measurement of the harmonic voltage on the medium-voltage side of the main transformer is accurate; if , the measurement of the harmonic voltage on the medium-voltage side of the main transformer is inaccurate.

7. The discrimination method for the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer in a substation according to claim 1, wherein The harmonic voltage on the medium voltage side of the main transformer is obtained through the following formula: ； ； In the formula, is the theoretical value of the phasor of the -th harmonic voltage on the medium-voltage side of the main transformer; is the -th harmonic voltage on the medium-voltage side of the main transformer; is the theoretical value of the real part of the phasor of the -th harmonic voltage on the medium-voltage side of the main transformer; is the theoretical value of the imaginary part of the phasor of the -th harmonic voltage on the medium-voltage side of the main transformer; is the phasor of the -th harmonic voltage equivalent to the neutral point of the main transformer on the high-voltage side; is the phasor of the -th harmonic current on the medium-voltage side of the main transformer; is the -th harmonic impedance equivalent to the winding on the medium-voltage side of the main transformer on the high-voltage side; is the turns ratio between the high-voltage and medium-voltage sides; is the harmonic order; is the imaginary unit.

8. The method for discriminating the measurement accuracy of harmonic voltage on the high-voltage and medium-voltage sides of the main transformer in a substation according to claim 1, wherein Identifying the measurement accuracy of the harmonic voltage on the high voltage side of the main transformer includes: Calculate the difference rate between the effective voltage value corresponding to the harmonic voltage on the high-voltage side of the main transformer and the phasor of the actually measured harmonic voltage on the high-voltage side, and use it as the harmonic voltage difference rate on the high-voltage side ; Compare the harmonic voltage difference rate on the high-voltage side with the harmonic threshold on the high-voltage side . If , the measurement of the harmonic voltage on the high-voltage side of the main transformer is accurate; if , the measurement of the harmonic voltage on the high-voltage side of the main transformer is inaccurate.

9. The method for discriminating the accuracy of harmonic voltage measurement on the high and medium voltage sides of the main transformer in a substation according to claim 1, characterized in that The harmonic voltage on the high voltage side of the main transformer is obtained through the following formula: ； ； Wherein, is the theoretical value of the phasor of the nth harmonic voltage on the high voltage side of the main transformer; The theoretical value of the phasor of the nth harmonic voltage; is the nth harmonic voltage on the high voltage side of the main transformer; The nth harmonic voltage; is the real part theoretical value of the phasor of the nth harmonic voltage on the high voltage side of the main transformer; The real part theoretical value of the phasor of the nth harmonic voltage; is the imaginary part theoretical value of the phasor of the nth harmonic voltage on the high voltage side of the main transformer; The imaginary part theoretical value of the phasor of the nth harmonic voltage; is the phasor of the nth harmonic voltage equivalent from the neutral point of the main transformer to the high voltage side; The phasor of the nth harmonic voltage equivalent from the neutral point of the main transformer to the high voltage side; is the phasor of the nth harmonic current on the high voltage side of the main transformer; The phasor of the nth harmonic current; is the nth harmonic impedance equivalent from the winding on the high voltage side of the main transformer to the high voltage side; The nth harmonic impedance; is the harmonic order; is the imaginary unit.

10. A discrimination system for the measurement accuracy of harmonic voltages on the high and medium voltage sides of the main transformer in a substation, characterized in that, Applying the method for discriminating the measurement accuracy of the harmonic voltage on the high and medium voltage sides of the main transformer of a substation according to any one of claims 1-9 includes: A data acquisition module for synchronously collecting the harmonic voltage phasors of the power supply buses on the high, medium, and low voltage sides of the main transformer in a substation and the harmonic current phasors of each outgoing line at the same time; An impedance modeling module for establishing equivalent impedance models for the high, medium, and low voltage sides of the main transformer according to the specification parameters of the main transformer; A neutral point module for calculating the harmonic voltage at the neutral point of the equivalent impedance model of the main transformer based on the harmonic voltage phasor and harmonic current phasor on the low voltage side; A medium voltage side discrimination module for calculating the harmonic voltage on the medium voltage side of the main transformer according to the collected harmonic current phasor on the medium voltage side and based on the harmonic voltage at the neutral point, and comparing it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the medium voltage side to identify the measurement accuracy of the harmonic voltage on the medium voltage side of the main transformer; A high voltage side discrimination module for calculating the harmonic voltage on the high voltage side of the main transformer according to the collected harmonic current phasor on the high voltage side and based on the harmonic voltage at the neutral point, and comparing it with the effective voltage value corresponding to the actually measured harmonic voltage phasor on the high voltage side to identify the measurement accuracy of the harmonic voltage on the high voltage side of the main transformer.

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