Low-frequency system fault judgment method and relay protection device based on electrical quantity calculation

Abstract

A low-frequency system fault judgment method and relay protection device based on electrical quantity calculation discretizes continuous electrical quantity signals into digital quantity sampling values ​​through a fixed sampling frequency, and then uses the current sampling value and the historical sampling value to calculate the effective value of the electrical quantity through the sampling value product algorithm. According to the instantaneous value of the electrical quantity and the effective value characteristics compared with the set action threshold, it can act quickly when the system fails. On the basis of ensuring reliability, the present invention can greatly improve the speed of low-frequency system relay protection, and avoid the expansion of the fault range or equipment damage caused by too slow protection action.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection, and specifically relates to a calculation method for low-frequency system relay protection, a low-frequency system fault judgment method based on electrical quantity calculation, and a relay protection device applying the fault judgment method. Background Art

[0002] Microcomputer relay protection devices are an important component of the first line of defense of the current power transmission system. Their basic principle is to discretize the AC electrical quantity signal of the protected object into a digital signal, and then extract the relevant characteristic quantities to make a tripping action or alarm output according to the preset logic.

[0003] The rated frequency of my country's power transmission system is 50Hz. Traditional thermal and hydroelectric generators all transmit electricity to the power grid at a rated frequency of 50Hz. Therefore, my country's relay protection devices mainly carry out algorithm research for 50Hz AC systems, and there is little research on low-frequency systems below 50Hz. With my country's increasing emphasis on clean energy, new energy such as wind power generation has become an important part of my country's energy strategy. New energy combined with flexible low-frequency AC transmission has become a new development direction, especially suitable for medium and long-distance offshore wind power transmission, onshore new energy collection and transmission, and long-distance power transmission in remote areas. Flexible low-frequency AC transmission has become a beneficial supplement to industrial frequency AC transmission and DC transmission.

[0004] In the prior art, there is little research on low-frequency protection algorithms. A relatively simple approach is to adapt the electrical quantity algorithm based on the 50Hz power frequency system to the low-frequency system by reducing the sampling frequency, that is, to ensure that the number of sampling points of a full AC cycle remains unchanged. Although this method is simple, it will greatly reduce the speed of the relay protection device. Taking the 20Hz low-frequency system as an example, the full-cycle algorithm time window of electrical quantities such as voltage and current will be extended from 20ms to 50ms; the half-wave integral algorithm time window will be extended from 10ms to 25ms. Obviously, the solution of reducing the sampling frequency is difficult to meet the requirements of relay protection speed. Summary of the invention

[0005] The purpose of the present invention is to provide a method for quickly calculating electrical quantities applied to low-frequency system relay protection and a method for judging low-frequency system faults based on electrical quantity calculation, so as to improve the speed of low-frequency system relay protection.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A low-frequency system fault judgment method based on electrical quantity calculation, characterized in that the low-frequency system fault judgment method comprises the following steps:

[0008] Step S1: Obtain the instantaneous value i of the electrical quantity at the current sampling point according to the fixed sampling frequencyk The electrical quantity effective value I is calculated by combining the instantaneous value of the electrical quantity at the historical sampling point and using the sampling value product algorithm. k ;

[0009] Step S2: Determine the absolute value of the instantaneous value of the electrical quantity |i k |Is it greater than or equal to I set *P, where I set is the set action threshold, P is the proportional coefficient; if yes, go to step S3, otherwise go to step S4;

[0010] Step S3: Determine the effective value I of the electrical quantity k Is it greater than or equal to I set If yes, go to step S5, otherwise go to step S6;

[0011] Step S4: Determine the effective value I of the electrical quantity k Is it less than I set If not, go to step S5; if yes, go to step S7;

[0012] Step S5: add 1 sampling interval Δt to the timer t, and then go to step S8;

[0013] Step S6: subtract one sampling interval time Δt from the timer t, and then go to step S1 to calculate the electrical quantity of the next sampling point;

[0014] Step S7: reset the timer t, and then go to step S1 to calculate the electrical quantity of the next sampling point;

[0015] Step S8: Determine whether the time counter t is greater than or equal to the set action time t set If yes, it is judged that the low-frequency system is faulty and the electrical quantity action flag is output; otherwise, go to step S1 to calculate the electrical quantity of the next sampling point.

[0016] Furthermore, the fixed sampling frequency in step S1 is not less than 1000 Hz.

[0017] Preferably, for a low-frequency system of 20 Hz, the sampling frequency is set to 1200 Hz.

[0018] Furthermore, the sampling value product algorithm in step S1 includes a two-sampling value product algorithm and a three-sampling value product algorithm.

[0019] Preferably, a two-sample product algorithm is used. For a 20 Hz low frequency system, the preferred time window of the two-sample algorithm is 6 sampling periods.

[0020] Furthermore, the step S2 is to set the action threshold, the proportional coefficient P, the range of which is The preferred value of P is 1.

[0021] Furthermore, the electrical quantity criterion action in step S8 can be used for direct tripping, and can also be used as an intermediate variable to participate in other protection logics.

[0022] The present application also discloses a relay protection device using a low-frequency system fault judgment method based on electrical quantity calculation, including an electrical quantity sampling module and an electrical quantity effective value calculation module; the characteristics are:

[0023] The relay protection device also includes an electrical quantity instantaneous value judgment module, an electrical quantity effective value judgment module, a timer, and an electrical quantity judgment action module;

[0024] The electrical quantity sampling module obtains the instantaneous value of the electrical quantity at the current sampling point according to a fixed sampling frequency. k The electrical quantity effective value calculation module uses the sampling value product algorithm to calculate the electrical quantity effective value I k ;

[0025] The magnitude relationship between the instantaneous value of the electrical quantity, the effective value of the electrical quantity and the action threshold is judged respectively by the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module;

[0026] According to the judgment results and timing time output by the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module, it is determined to collect the electrical quantity instantaneous value of the next sampling point through the electrical quantity sampling module, or to output the electrical quantity action mark through the electrical quantity judgment action module.

[0027] Further preferably, in the comparative analysis between the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module and the action threshold,

[0028] When the absolute value of the instantaneous value of the current electrical quantity is less than the product of the set action threshold and the proportional coefficient, and the effective value of the electrical quantity is also less than the set action threshold, the timer is reset and the instantaneous value of the electrical quantity at the next sampling point is collected through the electrical quantity sampling module;

[0029] When the absolute value of the instantaneous value of the current electrical quantity is less than the product of the set action threshold and the proportional coefficient, but the effective value of the electrical quantity is greater than or equal to the set action threshold, the timer is added with a sampling interval time Δt; then it is determined whether the timer time t is greater than or equal to the set action time t set If yes, the electrical quantity judgment action module outputs the electrical quantity action flag, otherwise the electrical quantity sampling module collects the instantaneous value of the electrical quantity at the next sampling point;

[0030] When the absolute value of the instantaneous value of the current electrical quantity is greater than or equal to the product of the set action threshold and the proportional coefficient, and the effective value of the electrical quantity is greater than or equal to the set action threshold, the timer is added with a sampling interval time Δt; then it is determined whether the timer time t is greater than or equal to the set action time t set If yes, the electrical quantity judgment action module outputs the electrical quantity action flag, otherwise the electrical quantity sampling module collects the instantaneous value of the electrical quantity at the next sampling point;

[0031] When the absolute value of the instantaneous value of the current electrical quantity is greater than or equal to the product of the set action threshold and the proportional coefficient, but the effective value of the electrical quantity is less than the set action threshold, the timer is reduced by 1 sampling interval time Δt, and then the instantaneous value of the electrical quantity at the next sampling point is collected through the electrical quantity sampling module.

[0032] Beneficial effects:

[0033] By adopting the method of the present invention, the speed of low-frequency system relay protection can be greatly improved on the basis of ensuring reliability, thereby avoiding the expansion of fault range or equipment damage caused by too slow protection action. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the low-frequency system fault judgment method based on electrical quantity calculation of the present invention;

[0035] Figure 2 It is a schematic diagram of electrical quantity waveform. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0037] A low-frequency system fault judgment method based on electrical quantity calculation includes the following steps: Figure 1 As shown, the implementation of the technical solution is further described in detail below.

[0038] Step S1: Obtain the instantaneous value i of the electrical quantity at the current sampling point according to the fixed sampling frequency k The electrical quantity effective value I is calculated by combining the instantaneous value of the electrical quantity at the historical sampling point and using the sampling value product algorithm. k ;

[0039] According to the sampling theorem, the continuous electrical quantity signal is discretized into a digital quantity signal through a fixed sampling frequency, and the sampling value at the current sampling moment is recorded as i k , then the adjacent historical sampling signals sampled at equal intervals are recorded as i k-1 、i k-2 、i k-3...etc. Using the current and historical sampling signals, the electrical quantity amplitude I can be obtained according to the two-sample value product or three-sample value product algorithm. k , preferably the following two-sample product algorithm is used:

[0040]

[0041] Among them, i k is the sampling value at the current sampling moment, i k-N Indicates the historical sampling value corresponding to N sampling points back at the current moment; ωT s is the angular frequency of the low-frequency electrical quantity signal, f is the frequency of the low-frequency electrical quantity signal, and f s is the sampling frequency; I k It is the effective value of the low-frequency electrical quantity signal.

[0042] By choosing a suitable sampling frequency f s And the number of fallback points N, the effective value of the electrical quantity signal I can be calculated according to the above formula k .

[0043] In order to further reduce the amount of calculation of formula (1), taking the low-frequency 20Hz transmission system as an example, the optimal sampling frequency f s is 1200 Hz, and the number of backoff points N is 5. After using the above preferred parameters, calculation formula (1) can be simplified to calculation formula (2):

[0044]

[0045] The time window required for calculation formula (2) is 6 sampling cycles, about 5ms, which can simply and quickly calculate the effective value of the electrical quantity.

[0046] Step S2: Determine the instantaneous value of the electrical quantity |i k |Is it greater than or equal to I set *P, where P is the proportionality coefficient. If yes, go to step S3, otherwise go to step S4;

[0047] The lower the value of proportional coefficient P, the higher the sensitivity but the lower the reliability; the higher the value of P, the higher the reliability but the corresponding sensitivity decreases. The recommended value range is Assuming that the electrical quantity waveform is a sine wave, and taking the most unfavorable 0° as the fault start angle, the fault waveform is as follows: Figure 2 Considering the relationship between the amplitude and effective value of the sinusoidal signal, if the instantaneous value |i k |>I set , then as the fault current increases, it can be considered that the fault electrical quantity must be greater than the action threshold I set , so the preferred P=1.

[0048] Step S3: Determine the effective value I of the electrical quantity k Is it greater than or equal to I set If yes, go to step S5, otherwise go to step S6;

[0049] In order to further improve the reliability of the criterion, the effective value I obtained by combining the sampling value product algorithm is k Determine the fault characteristics together. If the effective value I k At the fixed value I set If the above is true, it is confirmed that the fault characteristics are met.

[0050] Step S4: Determine the effective value I of the electrical quantity k Is it less than I set If not, go to step S5; if yes, go to step S7;

[0051] Step S5: add 1 sampling interval time Δt to the timer t, and then go to step S8;

[0052] Step S6: subtract one sampling interval time Δt from the timer t, and then go to step S1 to calculate the electrical quantity of the next sampling point;

[0053] Step S7: reset the timer t, and then go to step S1 to calculate the electrical quantity of the next sampling point;

[0054] When the instantaneous value |i k | and effective value I k Both are less than the fixed value I set Afterwards, it is determined that the electrical quantity does not meet the fault characteristics and the timer is cleared to 0.

[0055] Step S8: Determine whether the time counter t is greater than the set action time t set If yes, then output the electrical quantity judgment action; otherwise, go to step S1 to calculate the electrical quantity of the next sampling point.

[0056] When P is set to 1, Figure 2 As shown, I set The electrical quantity intersects at point A, and the electrical angle corresponding to point A is about 45°, corresponding to the 20Hz power transmission system and the preferred 1200Hz sampling rate. The electrical quantity reaches point A after about 8 sampling cycles from time 0, and the time window is about 6.7ms. This time window is larger than the time window of the product calculation formula (2) of the two sampling values ​​in step S1, that is, the effective value of the electrical quantity I can be obtained at time A. k If the effective value I at time A k Also greater than I set , then this algorithm can start the timer in step S5 after 6.7ms, greatly improving the speed of protection.

[0057] Furthermore, the electrical quantity criterion action outputted in step S8 can be used for direct tripping or as an intermediate variable to participate in other protection logics according to different application scenarios.

[0058] The present application also discloses a relay protection device including the aforementioned low-frequency system fault judgment method, including an electrical quantity sampling module, an electrical quantity effective value calculation module, an electrical quantity instantaneous value judgment module, an electrical quantity effective value judgment module, a timer, and an electrical quantity judgment action module.

[0059] The electrical quantity sampling module obtains the instantaneous value of the electrical quantity at the current sampling point according to a fixed sampling frequency. k The electrical quantity effective value calculation module uses the sampling value product algorithm to calculate the electrical quantity effective value I k ;

[0060] The magnitude relationship between the instantaneous value of the electrical quantity, the effective value of the electrical quantity and the action threshold is judged respectively by the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module;

[0061] According to the judgment results and timing time output by the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module, it is determined to collect the electrical quantity instantaneous value of the next sampling point through the electrical quantity sampling module, or to output the electrical quantity action mark through the electrical quantity judgment action module.

[0062] Further preferably, in the comparative analysis between the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module and the action threshold,

[0063] When the absolute value of the instantaneous value of the current electrical quantity is less than the product of the set action threshold and the proportional coefficient, and the effective value of the electrical quantity is also less than the set action threshold, the timer is reset and the instantaneous value of the electrical quantity at the next sampling point is collected through the electrical quantity sampling module;

[0064] When the absolute value of the instantaneous value of the current electrical quantity is less than the product of the set action threshold and the proportional coefficient, but the effective value of the electrical quantity is greater than or equal to the set action threshold, the timer is added with a sampling interval time Δt; then it is determined whether the timer time t is greater than or equal to the set action time t set If yes, the electrical quantity judgment action module outputs the electrical quantity action flag, otherwise the electrical quantity sampling module collects the instantaneous value of the electrical quantity at the next sampling point;

[0065] When the absolute value of the instantaneous value of the current electrical quantity is greater than or equal to the product of the set action threshold and the proportional coefficient, and the effective value of the electrical quantity is greater than or equal to the set action threshold, the timer is added with a sampling interval time Δt; then it is determined whether the timer time t is greater than or equal to the set action time t setIf yes, the electrical quantity judgment action module outputs the electrical quantity action flag, otherwise the electrical quantity sampling module collects the instantaneous value of the electrical quantity at the next sampling point;

[0066] When the absolute value of the instantaneous value of the current electrical quantity is greater than or equal to the product of the set action threshold and the proportional coefficient, but the effective value of the electrical quantity is less than the set action threshold, the timer is reduced by 1 sampling interval time Δt, and then the instantaneous value of the electrical quantity at the next sampling point is collected through the electrical quantity sampling module.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A low-frequency system fault judgment method based on electrical quantity calculation, characterized in that: The low-frequency system fault judgment method comprises the following steps: Step S1: Obtain the instantaneous value i of the electrical quantity at the current sampling point according to the fixed sampling frequency k The electrical quantity effective value I is calculated by combining the instantaneous value of the electrical quantity at the historical sampling point and using the sampling value product algorithm. k ; Step S2: Determine the absolute value of the instantaneous value of the electrical quantity |i k |Is it greater than or equal to I set *P, where I set is the set action threshold, P is the proportional coefficient; if yes, go to step S3, otherwise go to step S4; Step S3: Determine the effective value I of the electrical quantity k Is it greater than or equal to I set If yes, go to step S5, otherwise go to step S6; Step S4: Determine the effective value I of the electrical quantity k Is it less than I set If not, go to step S5; if yes, go to step S7; Step S5: add 1 sampling interval Δt to the timer t, and then go to step S8; Step S6: subtract one sampling interval time Δt from the timer t, and then go to step S1 to calculate the electrical quantity of the next sampling point; Step S7: reset the timer t, and then go to step S1 to calculate the electrical quantity of the next sampling point; Step S8: Determine whether the time counter t is greater than or equal to the set action time t set If yes, it is judged that the low-frequency system is faulty and the electrical quantity action flag is output; otherwise, go to step S1 to calculate the electrical quantity of the next sampling point.

2. The low-frequency system fault judgment method based on electrical quantity calculation according to claim 1 is characterized in that: The fixed sampling frequency in step S1 is not less than 1000 Hz.

3. The low-frequency system fault judgment method based on electrical quantity calculation according to claim 1 is characterized in that: For a low frequency system of 20 Hz, the fixed sampling frequency is set to 1200 Hz.

4. The low-frequency system fault judgment method based on electrical quantity calculation according to claim 1 or 3, characterized in that: The sampling value product algorithm in step S1 includes a two-sampling value product algorithm and a three-sampling value product algorithm.

5. The low-frequency system fault judgment method based on electrical quantity calculation according to claim 4 is characterized in that: In step S1, the effective value of the electrical quantity is calculated using a two-sample product algorithm; For a 20 Hz low frequency system, the time window of the two sampling value algorithm is 6 sampling periods.

6. The low-frequency system fault judgment method based on electrical quantity calculation according to claim 1 is characterized in that: In step S2, the value range of the proportional coefficient P is:

7. The low-frequency system fault judgment method based on electrical quantity calculation according to claim 6 is characterized in that: The value of P is 1.

8. The low-frequency system fault judgment method based on electrical quantity calculation according to claim 1 is characterized in that: In step S8, the electrical quantity criterion action can be used for direct tripping, or can be used as an intermediate variable to participate in other protection logics.

9. A relay protection device using the low-frequency system fault judgment method based on electrical quantity calculation as described in any one of claims 1 to 8, comprising an electrical quantity sampling module and an electrical quantity effective value calculation module; characterized in that: The relay protection device also includes an electrical quantity instantaneous value judgment module, an electrical quantity effective value judgment module, a timer, and an electrical quantity judgment action module; The electrical quantity sampling module obtains the instantaneous value of the electrical quantity at the current sampling point according to a fixed sampling frequency. k The electrical quantity effective value calculation module uses the sampling value product algorithm to calculate the electrical quantity effective value I k ; The magnitude relationship between the instantaneous value of the electrical quantity, the effective value of the electrical quantity and the action threshold is judged respectively by the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module; According to the judgment results and timing time output by the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module, it is determined to collect the electrical quantity instantaneous value of the next sampling point through the electrical quantity sampling module, or to output the electrical quantity action mark through the electrical quantity judgment action module.

10. The relay protection device according to claim 9, characterized in that: In the comparative analysis of the electrical quantity instantaneous value judgment module and the electrical quantity effective value judgment module and the action threshold, When the absolute value of the instantaneous value of the current electrical quantity is less than the product of the set action threshold and the proportional coefficient, and the effective value of the electrical quantity is also less than the set action threshold, the timer is reset and the instantaneous value of the electrical quantity at the next sampling point is collected through the electrical quantity sampling module; When the absolute value of the instantaneous value of the current electrical quantity is less than the product of the set action threshold and the proportional coefficient, but the effective value of the electrical quantity is greater than or equal to the set action threshold, the timer is added with a sampling interval time Δt; then it is determined whether the timer time t is greater than or equal to the set action time t set If yes, the electrical quantity judgment action module outputs the electrical quantity action flag, otherwise the electrical quantity sampling module collects the instantaneous value of the electrical quantity at the next sampling point; When the absolute value of the instantaneous value of the current electrical quantity is greater than or equal to the product of the set action threshold and the proportional coefficient, and the effective value of the electrical quantity is greater than or equal to the set action threshold, the timer is added with a sampling interval time Δt; then it is determined whether the timer time t is greater than or equal to the set action time t set If yes, the electrical quantity judgment action module outputs the electrical quantity action flag, otherwise the electrical quantity sampling module collects the instantaneous value of the electrical quantity at the next sampling point; When the absolute value of the instantaneous value of the current electrical quantity is greater than or equal to the product of the set action threshold and the proportional coefficient, but the effective value of the electrical quantity is less than the set action threshold, the timer is reduced by 1 sampling interval time Δt, and then the instantaneous value of the electrical quantity at the next sampling point is collected through the electrical quantity sampling module.

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