A general differential element design method based on hetero-side data linear normalization expansion

Abstract

The application discloses a kind of general differential element design methods based on heterolateral data linear normalization expansion, it is related to the technical field of power system relay protection, this method includes obtaining the rated power of each side of protected equipment, power factor and voltage transformer, current transformer rated parameter, setting expansion coefficient, calculating the secondary rated current of the reference side current transformer of protected equipment and the current balance coefficient of the n side;Synchronous sampling is carried out to the current of each side and is linearly expanded according to the balance coefficient, and difference current sampling sequence is generated;The effective value of difference current is calculated, and is normalized with the secondary rated current of the reference side current transformer, while the differential protection setting value, braking current and inflection point current are normalized;Proportional braking criterion is constructed to determine whether the action condition is met, and the protection action signal is output when it is met.The application improves the calculation precision of differential protection and the accuracy of proportional braking action, and enhances the universality and stability of multiple sides and different capacity devices.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and in particular to a general differential element design method based on linear normalized amplification of opposite-side data. Background Technology

[0002] Differential protection is an important main protection method in power systems for protecting electrical equipment such as transformers, generators, motors and busbars. Its basic principle is to compare the amplitude and phase relationship of the current on each side of the protected equipment. When an internal fault occurs, the differential current increases and meets the action criteria, thereby outputting a trip signal.

[0003] In practical engineering applications, the protected equipment is usually multi-sided (such as double-winding or triple-winding transformers), with different voltage levels, current transformer (CT) ratios, and voltage transformer (PT) parameters on each side, resulting in proportional differences in the sampled current on each side. Existing technologies typically achieve current balance through fixed-ratio conversion or simple ratio conversion, but these methods have shortcomings in the following aspects: Traditional differential protection is mostly calibrated based on the rated current of one side, and the parameters differ significantly between devices of different capacities, lacking a unified normalized benchmark, leading to complex protection setting; In digital protection devices, differential current calculation is usually implemented using a fixed-point algorithm. Because this involves multiple ratio conversions, Fourier calculations, and square root operations, quantization errors can easily occur without proper linear expansion processing, affecting operational accuracy; In existing implementations, because the differential current, braking current, and settings are not uniformly dimensional, there are deviations between the actual operating curve and the theoretical curve, especially in the high-current region. In multi-sided equipment, the transformer ratios, voltage levels, and capacities of each side's current transformers (CTs) differ. Using only simple proportional conversion can easily lead to systemic balance deviations, affecting the stability of differential protection. Therefore, how to construct a system that...

[0004] The secondary rated current is calculated uniformly based on the equipment's rated parameters; the current balance relationship on each side is unified through linear expansion; the fixed-point accuracy is maintained during the calculation of the effective value of the differential current; and the differential current and proportional braking criteria are uniformly normalized; thereby improving the operating accuracy of the proportional braking differential protection, reducing calculation errors, and making the actual operating curve closer to the theoretical operating curve, which has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the problem to be solved by the present invention is to address the problems existing in the current ratio conversion of multiple sides, insufficient accuracy of fixed point calculation, large deviation of proportional braking characteristics, and difficulty in unifying the setting values ​​between devices of different capacities in the existing differential protection technology.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] In a first aspect, embodiments of the present invention provide a general differential element design method based on linear normalized expansion of opposite-side data, including: obtaining the rated power, power factor and rated parameters of voltage transformers and current transformers on each side of the protected equipment, setting expansion coefficients, and calculating the secondary rated current of the reference side current transformer and the current balance coefficient on each side based on the rated parameters.

[0009] The current on each side of the protected equipment is sampled synchronously, and the sampled current on each side is linearly amplified according to the current balance coefficient to generate a differential current sampling sequence.

[0010] The effective value amplitude of the differential current is obtained by calculating the differential current sampling sequence.

[0011] The effective value amplitude of the differential current is normalized with the secondary rated current of the reference side current transformer to obtain the normalized value of the differential current, and the differential protection setting, braking current and inflection point current are normalized accordingly.

[0012] Based on the normalized differential current normalized value and the normalized differential protection setting value, a proportional braking criterion is constructed to determine whether the differential protection operation conditions are met. If they are met, a protection operation signal is output.

[0013] As a preferred embodiment of the general differential element design method based on linear normalized expansion of opposite-side data described in this invention, the method includes: calculating the secondary rated current of the reference-side current transformer and the current balance coefficient of each side based on the rated parameters, including:

[0014] Set the expansion factor k1 for the reference side equipment parameters. Based on the reference side rated power power, power factor cosφ, rated voltage PT11 of the primary winding of the reference side voltage transformer, rated current CT11 of the primary winding of the reference side current transformer, and rated current CT12 of the secondary winding of the reference side current transformer, calculate the reference side rated secondary current Ie, where Ie satisfies:

[0015] ;

[0016] As a preferred embodiment of the general differential element design method based on linear normalized expansion of opposite-side data described in this invention, the method further includes: calculating the secondary rated current of the reference-side current transformer and the current balance coefficient of each side based on the rated parameters; and further includes:

[0017] Set the current balance coefficient expansion factor k2, and perform parameter conversion on the rated voltage PTn1 of the primary winding of the nth voltage transformer, the rated current CTn1 of the primary winding of the nth current transformer, and the rated current CTn2 of the secondary winding of the nth current transformer to calculate the current balance coefficient BalCoffn on the nth side. BalCoffn satisfies the following:

[0018] ;

[0019] As a preferred embodiment of the general differential element design method based on linear normalized amplification of opposite-side data described in this invention, wherein: the sampled currents on each side are linearly amplified according to the current balance coefficient to generate a differential current sampling sequence, including:

[0020] The current on the reference side and each side of the protected equipment is sampled synchronously. A preset amplification factor and the current balance factor BalCoffn of the corresponding side are introduced, and the sampled current on each side is linearly proportionally converted.

[0021] The sampled currents from each side after linear amplification are weighted and summed.

[0022] ;

[0023] in, Let j be the j-th sampled value of the differential current. This is the j-th secondary current sampling value on the reference side of the device. This is the j-th secondary current sampling value on the n-th side of the device.

[0024] As a preferred embodiment of the general differential element design method based on linear normalized amplification of opposite-side data described in this invention, wherein: the differential current sampling sequence is calculated to obtain the effective value amplitude of the differential current, including:

[0025] Perform a Fourier operation on the differential current sampling sequence containing M sampling points, where j=0,1,2,…,M-1;

[0026] The real part of the difference current is calculated using the linear expanded Fourier algorithm. The formula for calculating the real part of the difference current is as follows:

[0027]

[0028] Where M is the number of sampling points in the Fourier algorithm, j is the sampling number, and k3 is the linear amplification coefficient for calculating the effective value amplitude of the differential current. This represents the real part of the difference current;

[0029] The formula for calculating the imaginary part of the differential current is:

[0030]

[0031] Where ΔIk is the imaginary part of the differential current, and ΔI is the effective value amplitude of the differential current;

[0032] The effective value amplitude of the differential current is calculated based on the real and imaginary parts of the differential current:

[0033] ;

[0034] As a preferred embodiment of the general differential element design method based on linear normalized amplification of opposite-side data described in this invention, the method involves normalizing the effective value amplitude of the differential current and the secondary rated current of the reference-side current transformer to obtain a normalized differential current value, including: The formula for calculating the normalized value of differential current is: ;

[0035] in, Ie is the normalized value of the differential current, and Ie is the normalized reference value.

[0036] As a preferred embodiment of the general differential element design method based on linear normalized amplification of opposite-side data described in this invention, wherein: the differential protection setting, braking current and inflection point current are normalized accordingly, including;

[0037] Obtain the differential protection setting, braking current, and inflection point current; use the secondary rated current of the reference side current transformer as a unified normalization reference, and perform normalization processing respectively.

[0038] Differential protection setting normalization value:

[0039] ;

[0040] Braking current normalization value:

[0041] ;

[0042] Inflection point current normalization value:

[0043] ;

[0044] Where Isetting is the differential protection setting, Isetting′ is the normalized value of the differential protection setting, Ibrake is the braking current, Ibrake′ is the normalized value of the braking current, Ig is the inflection point current of the proportional braking characteristic, and Ig′ is the normalized value of the inflection point current.

[0045] As a preferred solution of the general differential element design method based on linear normalized scaling of opposite-side data according to the present invention, wherein the proportional braking criterion is constructed based on the normalized differential current value and the normalized differential protection setting, and it is judged whether the differential protection operation condition is satisfied, and a protection operation signal is output if the condition is satisfied, which comprises:

[0046] Construct a proportional braking differential protection criterion function:

[0047] ;

[0048] wherein, k is the proportional braking coefficient;

[0049] wherein, if Ibrake<Ig, it is specified that Ibrake-Ig=0;

[0050] When the criterion condition is satisfied, a differential protection operation signal is output; otherwise, the protection remains non-operating.

[0051] In a second aspect, an embodiment of the present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program instructions are executed by the processor, the steps of the general differential element design method based on linear normalized scaling of opposite-side data according to the first aspect of the present invention are implemented.

[0052] In a third aspect, an embodiment of the present invention provides a computer-readable storage medium, on which a computer program is stored, and when the computer program instructions are executed by a processor, the steps of the general differential element design method based on linear normalized scaling of opposite-side data according to the first aspect of the present invention are implemented.

[0053] The beneficial effects of the present invention are: the present invention calculates the secondary rated current of the current transformer on the reference side based on the rated parameters of the device, and constructs the current balance coefficient of each side, so that multi-side currents of different voltage levels and different current transformer transformation ratios are unified to the same proportional reference, which reduces the systematic balance error caused by parameter differences and improves the stability of differential protection. A linear scaling coefficient is introduced in the processes of rated current calculation, current balance processing and Fourier effective value calculation to form a unified scaling calculation system, which effectively reduces the quantization error in digital fixed-point operation, improves the numerical calculation accuracy, and makes the protection operation value closer to the theoretical calculation result. The effective value of differential current, the differential protection setting, the braking current and the inflection point current are uniformly normalized, so that the dimensions on both sides of the proportional braking criterion are consistent, avoiding the influence from different capacities or different rated parameters, and making the actual operation curve more fit the theoretical proportional braking characteristic curve. Description of Drawings

[0054] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a line graph showing the operation of the proportional differential protection before and after the expansion of the present invention. Detailed Implementation

[0056] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0057] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0058] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0059] Example 1

[0060] Reference Figures 1-2 This is the first embodiment of the present invention, which provides a general differential element design method based on linear normalized amplification of opposite-side data, including:

[0061] S1: Obtain the rated power, power factor, and rated parameters of voltage transformers and current transformers on each side of the protected equipment, set the expansion factor, and calculate the secondary rated current of the reference side current transformer and the current balance coefficient on each side based on the rated parameters.

[0062] Furthermore, a parameter expansion factor k1 is set for the reference-side equipment. Based on the reference-side rated power power, power factor cosφ, rated voltage PT11 of the primary winding of the reference-side voltage transformer, rated current CT11 of the primary winding of the reference-side current transformer, and rated current CT12 of the secondary winding of the reference-side current transformer, the rated secondary current Ie of the reference-side current transformer is calculated, wherein Ie satisfies:

[0063] ;

[0064] Furthermore, setting the current balance coefficient expansion factor k2, parameter conversion is performed on the rated voltage PTn1 of the primary winding of the nth voltage transformer, the rated current CTn1 of the primary winding of the nth current transformer, and the rated current CTn2 of the secondary winding of the nth current transformer to calculate the current balance coefficient BalCoffn on the nth side. BalCoffn satisfies the following:

[0065] ;

[0066] It should be noted that by setting the basic setpoints power, cosφ, and n (n is an integer and generally 2≤n≤20), the interrupt program automatically generates the current transformer parameter setpoints for PT11, PT12, CT11, CT12, PT21, PT22, CT21, CT22...PTn1, PTn2, CTn1, CTn2, etc., based on the specific value of n. Then, based on the actual parameters of the equipment, the above basic setpoints and current transformer parameter setpoints are adjusted, and the interrupt program calculates the current balance coefficient BalCoffn on each side according to the above formula.

[0067] S2: The current on each side of the protected equipment is sampled synchronously, and the sampled current on each side is linearly amplified according to the current balance coefficient to generate a differential current sampling sequence.

[0068] Furthermore, the current on the reference side and each side of the protected equipment is sampled synchronously, and a preset amplification factor and the current balance factor BalCoffn of the corresponding side are introduced to perform linear proportional conversion on the sampled current of each side.

[0069] The sampled currents from each side after linear amplification are weighted and summed.

[0070] ;

[0071] in, Let j be the j-th sampled value of the differential current. This is the j-th secondary current sampling value on the reference side of the device. This is the j-th secondary current sampling value on the n-th side of the device.

[0072] It should be noted that if the sampling frequency is 8kHz, the ADC internal sample-and-hold circuit is used. After the ADC sampling operation is started, the input signals of all channels are held and sampled and converted at the same time. After the conversion of all channels is completed, the ADC chip outputs a conversion completion signal. The processor or FPGA reads the sampled values ​​of all channels through the parallel port or serial port.

[0073] S3: Calculate the effective value amplitude of the differential current by performing a calculation on the differential current sampling sequence.

[0074] Furthermore, a Fourier operation is performed on the differential current sampling sequence containing M sampling points, where j=0,1,2,…,M-1;

[0075] The real part of the difference current is calculated using the linear expanded Fourier algorithm. The formula for calculating the real part of the difference current is as follows:

[0076] ;

[0077] Where M is the number of sampling points in the Fourier algorithm, j is the sampling number, and k3 is the linear amplification coefficient for calculating the effective value amplitude of the differential current. This represents the real part of the difference current;

[0078] The formula for calculating the imaginary part of the differential current is:

[0079]

[0080] Where ΔIk is the imaginary part of the differential current, and ΔI is the effective value amplitude of the differential current;

[0081] The effective value amplitude of the differential current is calculated based on the real and imaginary parts of the differential current:

[0082] ;

[0083] S4: Normalize the effective value amplitude of the differential current and the secondary rated current of the reference side current transformer to obtain the normalized value of the differential current, and perform corresponding normalization on the differential protection setting, braking current and inflection point current.

[0084] Furthermore, the formula for calculating the normalized value of the differential current is: ;

[0085] in, Ie is the normalized value of the differential current, and Ie is the normalized reference value.

[0086] Furthermore, the differential protection setting, braking current, and inflection point current are obtained; the secondary rated current of the reference side current transformer is used as a unified normalization reference, and normalization processing is performed respectively.

[0087] Differential protection setting normalization value:

[0088] ;

[0089] Braking current normalization value:

[0090] ;

[0091] Normalized inflection point current:

[0092] ;

[0093] wherein, Isetting is the differential protection setting, Isetting′ is the normalized differential protection setting, Ibrake is the braking current, Ibrake′ is the normalized braking current, Ig is the inflection point current of the proportional braking characteristic, and Ig′ is the normalized inflection point current.

[0094] It should be noted that the measurement results before and after adopting the normalized scaling algorithm are shown in the following table:

[0095]

[0096] Table 1 Comparison table of measurement errors before and after adopting the normalized scaling algorithm

[0097] It can be seen from Figure 2 that after adopting the normalized scaling calibration algorithm, the operating broken line of the proportional braking differential protection is closer to the theoretical operating broken line.

[0098] S5: Constructing a proportional braking criterion based on the normalized differential current and the normalized differential protection setting, determining whether the differential protection operating condition is satisfied, and outputting a protection operating signal if the condition is satisfied.

[0099] Further, constructing a proportional braking criterion based on the normalized differential current and the normalized differential protection setting, determining whether the differential protection operating condition is satisfied, and outputting a protection operating signal if the condition is satisfied comprises:

[0100] Constructing a proportional braking differential protection criterion function:

[0101] ;

[0102] wherein, k is the proportional braking coefficient;

[0103] wherein, if Ibrake < Ig, it is specified that Ibrake-Ig=0;

[0104] when the criterion condition is satisfied, outputting a differential protection operating signal, otherwise keeping the protection not operating.

[0105] The present embodiment further provides a computer device, which is applicable to a general differential element design method based on linear normalized scaling of opposite-side data, comprising a memory and a processor; the memory is configured to store computer executable instructions, and the processor is configured to execute the computer executable instructions to implement the general differential element design method based on linear normalized scaling of opposite-side data proposed in the above embodiments.

[0106] The computer device can be a terminal, comprising a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0107] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements a general differential element design method based on linear normalized expansion of opposite-side data as proposed in the above embodiment.

[0108] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A general differential element design method based on linear normalized amplification of opposite-side data, characterized in that, include: Obtain the rated power, power factor, and rated parameters of voltage transformers and current transformers on each side of the protected equipment; set the expansion factor; and calculate the secondary rated current of the reference side current transformer and the current balance factor of the nth side based on the rated parameters. The current on each side of the protected equipment is sampled synchronously, and the sampled current on each side is linearly amplified according to the current balance coefficient to generate a differential current sampling sequence. The effective value amplitude of the differential current is obtained by calculating the differential current sampling sequence. The effective value amplitude of the differential current is normalized with the secondary rated current of the reference side current transformer to obtain the normalized value of the differential current, and the differential protection setting, braking current and inflection point current are normalized accordingly. Based on the normalized differential current normalized value and the normalized differential protection setting value, a proportional braking criterion is constructed to determine whether the differential protection operation conditions are met. If they are met, a protection operation signal is output.

2. The general differential element design method based on linear normalized amplification of opposite-side data as described in claim 1, characterized in that, The calculation of the secondary rated current of the reference-side current transformer and the current balance coefficient of the nth side based on the rated parameters includes: Set the expansion factor k1 for the reference side equipment parameters. Based on the reference side rated power power, power factor cosφ, rated voltage PT11 of the primary winding of the reference side voltage transformer, rated current CT11 of the primary winding of the reference side current transformer, and rated current CT12 of the secondary winding of the reference side current transformer, calculate the reference side rated secondary current Ie, where Ie satisfies: 。 3. The general differential element design method based on linear normalized amplification of opposite-side data as described in claim 1, characterized in that, The calculation of the secondary rated current of the reference-side current transformer and the current balance coefficient of the nth side based on the rated parameters also includes: Set the current balance coefficient expansion factor k2, and perform parameter conversion on the rated voltage PTn1 of the primary winding of the nth voltage transformer, the rated current CTn1 of the primary winding of the nth current transformer, and the rated current CTn2 of the secondary winding of the nth current transformer to calculate the current balance coefficient BalCoffn on the nth side. BalCoffn satisfies the following: 。 4. The general differential element design method based on linear normalized amplification of opposite-side data as described in claim 1, characterized in that, The step of linearly amplifying the sampled currents on each side according to the current balance coefficient to generate a differential current sampling sequence includes: The current on the reference side and each side of the protected equipment is sampled synchronously. A preset amplification factor and the current balance factor BalCoffn of the corresponding side are introduced, and the sampled current on each side is linearly proportionally converted. The sampled currents from each side after linear amplification are weighted and summed. ； in, Let j be the j-th sampled value of the differential current. This is the j-th secondary current sampling value on the reference side of the device. This is the j-th secondary current sampling value on the n-th side of the device.

5. The general differential element design method based on linear normalized amplification of opposite-side data as described in claim 1, characterized in that, The calculation of the differential current sampling sequence to obtain the effective value amplitude of the differential current includes: Perform a Fourier operation on the differential current sampling sequence containing M sampling points, where j=0,1,2,…,M-1; The real part of the difference current is calculated using the linear expanded Fourier algorithm. The formula for calculating the real part of the difference current is as follows: ； Where M is the number of sampling points in the Fourier algorithm, j is the sampling number, and k3 is the linear amplification coefficient for calculating the effective value amplitude of the differential current. This represents the real part of the difference current; The formula for calculating the imaginary part of the differential current is: ； Where ΔIk is the imaginary part of the differential current, and ΔI is the effective value amplitude of the differential current; The effective value amplitude of the differential current is calculated based on the real and imaginary parts of the differential current: 。 6. The general differential element design method based on linear normalized amplification of opposite-side data as described in claim 1, characterized in that, The step of normalizing the effective value amplitude of the differential current with the secondary rated current of the reference-side current transformer to obtain the normalized differential current value includes: The formula for calculating the normalized differential current value is as follows: ; in, Ie is the normalized value of the differential current, and Ie is the normalized reference value.

7. The general differential element design method based on linear normalized amplification of opposite-side data as described in claim 1, characterized in that, The method includes normalizing the differential protection settings, braking current, and inflection point current, including: Obtain differential protection settings, braking current, and inflection point current; Performing normalization processing separately by taking the secondary rated current of said reference side current transformer as a unified normalization reference; Normalized value of differential protection setting: ； Normalized value of braking current: ； Normalized value of inflection point current: ； wherein, Isetting is the differential protection setting, Isetting′ is the normalized value of the differential protection setting, Ibrake is the braking current, Ibrake′ is the normalized value of the braking current, Ig is the inflection point current of the proportional braking characteristic, and Ig′ is the normalized value of the inflection point current.

8. The general differential element design method based on linear normalized amplification of opposite-side data as described in claim 1, characterized in that, Said constructing a proportional braking criterion based on the normalized differential current value after normalization and the normalized differential protection setting, judging whether the differential protection action condition is satisfied, and outputting a protection action signal if the condition is satisfied, comprises: Constructing a proportional braking differential protection criterion function: ； wherein, k is the proportional braking coefficient; wherein, if Ibrake < Ig, it is specified that Ibrake - Ig = 0; When said criterion condition is satisfied, output a differential protection action signal; otherwise, keep the protection not acting.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When said processor executes said computer program, the steps of a general differential element design method based on linear normalized scaling of opposite-side data according to any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When said computer program is executed by a processor, the steps of a general differential element design method based on linear normalized scaling of opposite-side data according to any one of claims 1 to 8 are implemented.

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