Generator machine end zero sequence CT abnormality discrimination method

Abstract

The application discloses a generator terminal zero sequence CT abnormality discrimination method, first, real-time data of a generator terminal three-phase voltage, a generator terminal zero sequence voltage, a generator terminal three-phase current and a generator terminal zero sequence CT current are collected, then a full-cycle Fourier series calculation method is used to calculate the fundamental wave components of the generator terminal three-phase voltage, the generator terminal zero sequence voltage, the generator terminal three-phase current and the generator terminal zero sequence CT current, finally, the generator terminal positive sequence voltage, the generator terminal three-phase current maximum value, the generator terminal fundamental wave zero sequence voltage mutation value and the generator terminal fundamental wave zero sequence current mutation value are calculated, when the generator terminal positive sequence voltage is greater than a constant value 1 and the generator terminal zero sequence voltage is less than a constant value 2, then the generator terminal zero sequence CT abnormality logical discrimination is carried out, if criterion 1 and criterion 2 are both satisfied in the logical discrimination, then the delay alarm is carried out. The generator terminal zero sequence CT abnormality criterion with the ratio brake threshold and the mutation value threshold characteristics is used to realize the generator terminal zero sequence CT abnormality discrimination, the reliability of the criterion is ensured, and the sensitivity of the criterion is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of power systems, and particularly relates to a generator terminal zero sequence CT abnormality discrimination method. BACKGROUND

[0002] The generator terminal zero sequence CT is used for measuring the zero sequence current of the generator stator ground fault, realizing the generator zero sequence overcurrent stator ground protection or the generator zero sequence direction selection stator ground protection, and is widely applied to small and medium-sized generator units, especially the wiring mode of the generator terminal common bus, also known as the "multi-machine and one transformer" expanded unit wiring mode. The papers "Analysis of Selective Stator Grounding Protection of Zero Sequence Direction Element" (Journal of Jiangsu Electrical Engineering, written by Tan Tao et al.) and "Research and Application of Selective Stator Grounding Protection Based on Flexible Optical Transformer" (Hydropower and Pumping Storage, written by Li Huazhong et al.) all indicate that the key point of realizing the selective stator grounding protection is to accurately and correctly realize the zero sequence current measurement of the generator stator ground fault. For the field conditions, the terminal zero sequence CT is installed at the generator terminal, and the field installation environment is often relatively poor, and the following problems exist: (1) The terminal zero sequence CT is often installed at the bridge, corridor and other positions, and the conductor position change of the terminal zero sequence CT is easily caused by the mechanical vibration of the generator unit, human error and other reasons, thereby causing the measurement change of the terminal zero sequence CT, and leading to the collection of false zero sequence current by the protection device; (2) The terminal zero sequence CT and the lead wire are in an environment with large electromagnetic interference, and the lead wire of the terminal zero sequence CT passes through multiple interval layers to the protection device screen cabinet, and the terminal zero sequence CT current is easily caused by electromagnetic interference to cause inaccurate measurement. Based on the above conditions, the terminal zero sequence CT measurement is inaccurate, and even false zero sequence current appears, and finally incorrect action of the protection device is caused, so it is of great significance to realize the abnormality discrimination of the terminal zero sequence CT. SUMMARY

[0003] The purpose of the application is to provide a generator terminal zero sequence CT abnormality discrimination method, which can effectively avoid the incorrect action of the stator grounding protection caused by the abnormality of the terminal zero sequence CT, and can check the measurement loop of the terminal zero sequence CT in time and eliminate the fault after the alarm.

[0004] In order to achieve the above purpose, the solution of the application is:

[0005] A generator terminal zero sequence CT abnormality discrimination method, comprising the following steps:

[0006] Step 1: collecting real-time data of the terminal three-phase voltage, the terminal zero sequence voltage, the terminal three-phase current and the terminal zero sequence current of the generator;

[0007] Step 2: The real-time data collected is calculated by using the Fourier series calculation method of full wave to obtain the fundamental components of the three-phase voltage at the generator terminal, the zero-sequence voltage at the generator terminal, the three-phase current at the generator terminal and the zero-sequence current at the generator terminal;

[0008] Step 3: The positive-sequence voltage at the generator terminal is calculated according to the fundamental component of the three-phase voltage at the generator terminal, the maximum effective value of the three-phase current is calculated according to the fundamental component of the three-phase current at the generator terminal, the fundamental zero-sequence voltage mutation at the generator terminal is calculated according to the fundamental component of the zero-sequence voltage at the generator terminal, and the fundamental zero-sequence current mutation at the generator terminal is calculated according to the fundamental component of the zero-sequence current at the generator terminal;

[0009] Step 4: When the positive-sequence voltage at the generator terminal is greater than a constant value U 1_th and the fundamental zero-sequence voltage at the generator terminal is less than a constant value 3U 0_th , proceed to Step 5, otherwise end the abnormality judgment of the zero-sequence CT at the generator terminal;

[0010] Step 5: The following logical judgment is performed, when criterion 1 and criterion 2 are both met, delay alarm is performed;

[0011] Criterion 1: 3I0>m×I max +3I 0th ,

[0012] Criterion 2: (Δ3I0≥Δ3I 0_th and Δ3U0<Δ3U 0_th ) or (Δ3I0<Δ3I 0_th and Δ3U0≥Δ3U 0_th ), wherein 3I0 is the fundamental zero-sequence current at the generator terminal, m is a ratio braking coefficient, I max is the maximum effective value of the three-phase fundamental current at the generator terminal, 3I 0th is the fixed zero-drift threshold of the zero-sequence current at the generator terminal, Δ3I0 is the fundamental zero-sequence current mutation at the generator terminal, Δ3I 0_th is the fundamental zero-sequence current mutation threshold, Δ3U0 is the fundamental zero-sequence voltage mutation at the generator terminal, and Δ3U 0_th is the fundamental zero-sequence voltage mutation threshold.

[0013] Optionally, the calculation formula for calculating the fundamental zero-sequence voltage mutation at the generator terminal in Step 3 is:

[0014] Δ3U0=|3U0(k)-3U0(k-j×N)| Formula (1)

[0015] The formula for calculating the fundamental zero-sequence current mutation at the generator terminal in Step 3 is:

[0016] Δ3I0=|3I0(k)-3I0(k-j×N)| Formula (2)

[0017] Wherein, 3U0(k) is the effective value of the fundamental zero-sequence voltage at point k, and k is the current point identifier; 3U0(kj×N) is the effective value of the fundamental zero-sequence voltage at point (kj×N), where N is the number of sampling points for one power frequency cycle, and j is a fixed positive integer; 3I0(k) is the effective value of the fundamental zero-sequence current at point k, and 3I0(kj×N) is the effective value of the fundamental zero-sequence current at point (kj×N).

[0018] Optionally, the fixed value U in step 4 1_th The value range is 80% to 110% of the effective value of the generator's secondary rated phase voltage; the set value 3U in step 4. 0_th The value range is 5% to 20% of the effective value of the generator's secondary rated phase voltage.

[0019] Optionally, in step 5, the ratio braking coefficient m ranges from (0.01, 0.30); the fixed zero drift threshold 3I 0th The value range is (0.002I). n 0.100I n ), I n The secondary side value of the generator terminal CT; the threshold Δ3I for the sudden change in the fundamental zero-sequence current at the generator terminal. 0_th The value range is (0.005A, 1.000A), and the threshold for the fundamental zero-sequence voltage mutation at the machine terminal is Δ3U. 0_th The value range is (0.50V, 10.00V).

[0020] The beneficial effects of adopting the above solution are as follows:

[0021] This invention employs a zero-sequence CT anomaly criterion with ratio braking threshold and sudden change threshold characteristics to achieve zero-sequence CT anomaly discrimination. Since the criterion has current ratio braking characteristics, the action threshold is increased, which can effectively prevent criterion misjudgment and improve the reliability of the criterion. At the same time, the use of sudden change threshold criterion also effectively improves the sensitivity of the criterion. Attached Figure Description

[0022] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0023] The following will take the parameters of a domestic generating unit as an example, combined with... Figure 1 The process steps shown below provide a detailed explanation of the technical solution of this invention.

[0024] A domestic power plant uses a two-generator-one-transformer configuration. The generator capacity is 45MW, frequency is 50Hz, power factor is 0.9, generator terminal voltage is 13.8kV, generator terminal rated current is 2138A, and the generator terminal voltage PT ratio is: Generator terminal CT turns ratio 2500A / 1A, generator terminal CT secondary side value I n = 1A, generator terminal secondary rated phase voltage 3U0= 57.74V, constant value U 1_th = 48V, constant value 3U 0_th = 10V, ratio braking coefficient m is 0.1, generator terminal zero sequence current fixed zero drift threshold 3I 0th = 0.1xI n = 0.1x1 = 0.1A, generator terminal fundamental zero sequence current threshold of sudden change Δ3I 0_th = 0.05A, generator terminal fundamental zero sequence current threshold of sudden change Δ3U 0_th = 0.5V.

[0025] Step 1: Collect real-time data of generator terminal three-phase voltage, generator terminal zero sequence voltage, generator terminal three-phase current and generator terminal zero sequence current;

[0026] Step 2: Calculate the generator terminal three-phase fundamental voltage respectively by using full cycle Fourier series calculation method Calculate the current value of generator terminal fundamental zero sequence voltage The effective value 3U0 of the current value is 0.5V, and the value of the generator terminal zero sequence voltage 3 cycles ago is The corresponding effective value 3U0(0-3x24) is 0.4V; the generator terminal three-phase fundamental current is respectively The current value of generator terminal fundamental zero sequence current The effective value 3I0 of the current value is 0.2A, and the value of the generator terminal zero sequence voltage 3 cycles ago is The corresponding effective value 3I0(0-3x24) is 0.4A;

[0027] Step 3: Calculate the generator terminal positive sequence voltage by using the generator terminal three-phase fundamental voltage

[0028]

[0029] The effective value U1 of the generator terminal positive sequence voltage is 57.73V,

[0030] Calculate the maximum effective value of three-phase current by using the generator terminal three-phase fundamental current The result in the formula is the effective value;

[0031] Calculate the generator terminal fundamental zero sequence voltage sudden change:

[0032] Δ3U0 = |3U0(k)-3U0(k-jxN)| = |3U0(0)-3U0(0-3x24)|

[0033] = |0.5V-0.4V| = 0.1V

[0034] The result in the formula is taken effective value,

[0035] The formula of the computer terminal fundamental wave zero sequence current mutation is:

[0036] Δ3I0=|3I0(k)-3I0(k-j×N)|=|3I0(0)-3I0(0-3×24)|

[0037] =|0.2A-0.4A|=0.2A

[0038] Step 4: when the generator terminal positive sequence voltage U1=57.74V is greater than the fixed value U 1_th =48V and the terminal fundamental wave zero sequence voltage 3U0=0.5V is less than the fixed value 3U 0_th =10V, step 5 is entered;

[0039] Step 5: the following logical discrimination is carried out,

[0040] Criterion 1: 3I0=0.2>m×I max +3I 0th =0.10×0.855+0.1=0.18A,

[0041] Criterion 2: (Δ3I0=0.2≥Δ3I 0_th =0.05 and Δ3U0=0.1<Δ3U 0_th =0.5) (the condition is met) or (Δ3I0<Δ3I 0_th and Δ3U0≥Δ3U 0_th ) (the condition is not met), criterion 2 is met,

[0042] then criterion 1 and criterion 2 are finally met, and the delay alarm is carried out.

[0043] The above examples only illustrate the technical idea of the present application, and cannot limit the protection scope of the present application, any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the present application.

Claims

1. A method for identifying zero-sequence CT anomalies at generator terminals, characterized in that, It includes the following steps: Step 1: Collect real-time data of generator terminal three-phase voltage, generator terminal zero-sequence voltage, generator terminal three-phase current and generator terminal zero-sequence current; Step 2: Using the full-cycle Fourier series calculation method, the collected real-time data is calculated to obtain the fundamental components of the three-phase voltage, zero-sequence voltage, three-phase current, and zero-sequence current at the generator terminals. Step 3: Calculate the positive sequence voltage at the generator terminal based on the fundamental component of the three-phase voltage at the generator terminal; calculate the maximum effective value of the three-phase current based on the fundamental component of the three-phase current at the generator terminal; calculate the abrupt change of the fundamental zero-sequence voltage at the generator terminal based on the fundamental component of the zero-sequence voltage at the generator terminal; calculate the abrupt change of the fundamental zero-sequence current at the generator terminal based on the fundamental component of the zero-sequence current at the generator terminal. Step 4: When the positive sequence voltage at the generator terminals is greater than the set value And the fundamental zero-sequence voltage at the machine terminal is less than a set value. If the condition is met, proceed to step 5; otherwise, terminate the zero-sequence CT anomaly detection on the machine. Step 5: Perform the following logical judgment, and trigger a delayed alarm when both criterion 1 and criterion 2 are satisfied simultaneously; Criterion 1: ; Criterion 2: or ; in, The terminal fundamental zero-sequence current, This is the ratio braking coefficient. This is the maximum effective value of the three-phase fundamental current at the generator terminals. Set a fixed zero-drift threshold for the zero-sequence current at the machine terminal; This refers to the sudden change in the fundamental zero-sequence current at the machine terminal. The threshold for the sudden change in the fundamental zero-sequence current at the machine terminal; This refers to the sudden change in the fundamental zero-sequence voltage at the machine terminal. This is the threshold for the fundamental zero-sequence voltage mutation at the machine terminal.

2. The generator terminal zero-sequence CT anomaly detection method as described in claim 1, characterized in that, The formula for the fundamental zero-sequence voltage mutation at the computer end in step 3 is: The formula for the abrupt change in the fundamental zero-sequence current at the computer end in step 3 is: in, The dot is The effective value of the fundamental zero-sequence voltage at the machine terminal. This serves as the identifier for the current point. The dot is The corresponding effective value of the fundamental zero-sequence voltage at the machine terminal. The number of sampling points for one power frequency cycle. It is a fixed positive integer; The dot is The effective value of the fundamental zero-sequence current at the machine terminal. The dot is The corresponding effective value of the fundamental zero-sequence current at the machine terminal.

3. The generator terminal zero-sequence CT anomaly detection method as described in claim 1, characterized in that, The fixed value in step 4 The value range is 80% to 110% of the effective value of the generator's secondary rated phase voltage; the set value in step 4 The value range is 5% to 20% of the effective value of the generator's secondary rated phase voltage.

4. The generator terminal zero-sequence CT anomaly detection method as described in claim 1, characterized in that, The ratio braking coefficient in step 5 The value range is (0.01, 0.30); the zero-sequence current at the terminal is fixed at the zero-drift threshold. The value range is (0.002). 0.100 ), For the secondary side value of the generator terminal CT; threshold for the sudden change in the fundamental zero-sequence current at the generator terminal. The value range is (0.005A, 1.000A), which is the threshold for the fundamental zero-sequence voltage mutation at the machine terminal. The value range is (0.50V, 10.00V).

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