A quality inspection system for power system installation

Abstract

The invention discloses a quality inspection system for power system installation, and the invention relates to the technical field of power system installation; the invention realizes the measurement of grounding resistance under different input voltages through the arrangement of a power supply unit, a grounding resistance measuring unit and a resistance compensation unit, and accurately measures the voltage realized by multiple acquisition of output voltage and filtering, and further reduces the measurement error by combining the acquisition and processing of resistance voltage value, realizes accurate sampling of grounding resistance voltage and reduces circuit interference, and optimizes the circuit structure so that the entire grounding resistance measurement circuit has a simple structure, strong reliability, little external interference and good stability.

Description

Technical Field

[0001] The present invention relates to the technical field of power system installation, and in particular to a quality inspection system for power system installation. Background Art

[0002] The quality inspection system installed in the power system is to ensure the electrical safety and reliable operation of the building, prevent equipment failures, reduce power problems, and improve the overall operating efficiency and sustainability of the building facilities. This requires the inspection of the quality inspection system to determine whether the power system can meet the expected design requirements. The quality inspection of the power system is a complete and strictly standardized process, which requires various tests on each device in the power system and the entire power system.

[0003] In the prior art, in the power system of an office building, the potential difference formed by the fault voltage to the ground conducted by the casing, pipelines, building structures, metal conductors, etc. of the power equipment may cause casualties or electrical fires. Therefore, there are strict requirements for the grounding resistance. The smaller the grounding resistance, the better the current flow. When there is leakage or lightning strike, the electricity is discharged to the ground through the grounding wire. The faster the discharge, the safer it is. The independent lightning protection grounding resistance should be less than or equal to 10 ohms, the independent safety protection grounding resistance should be less than or equal to 4 ohms, the independent AC working grounding resistance and the independent DC working grounding resistance should also be less than or equal to 4 ohms, and the shared grounding body (combined grounding) should not be greater than the grounding resistance of 1 ohm. Therefore, in order to ensure the safe use of the power system, it is necessary to measure the grounding resistance after the power system is installed. During this measurement process, the measured circuit system is relatively complex and the accuracy is low.

[0004] In view of the above technical defects, a solution is now proposed. Summary of the invention

[0005] The purpose of the present invention is to measure the grounding resistance under different input voltages through the setting of a power supply unit, a grounding resistance measuring unit and a resistance compensation unit, and accurately measure the voltage achieved by multiple acquisitions of the output voltage and filtering, and further reduce the measurement error by combining the acquisition and processing of the resistance voltage value, thereby achieving accurate sampling of the grounding resistance voltage and reducing circuit interference. By optimizing the circuit structure, the entire grounding resistance measurement circuit has a simple structure, strong reliability, little external interference and good stability.

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

[0007] A quality inspection system for power system installation includes a power supply unit, a grounding resistance measuring unit and a resistance compensation unit. The power supply unit includes a power supply device, a switching circuit, a filter, and a variable isolation transformer T1. The input end of the filter is electrically connected to the power supply device, and the output end is electrically connected to the variable isolation transformer T1. The switching circuit is arranged in series between the power supply device and the variable isolation transformer T1. The power supply unit and the grounding resistance measuring unit are electrically connected through the variable isolation transformer T1. The grounding resistance measuring unit includes a grounding device simulation resistor R0, an amplifying resistor R1, a protective resistor R2 and a voltage sampling circuit, and the grounding device simulation resistor R0, the amplifying resistor R1 and the protective resistor R2 are arranged in series in sequence, the voltage sampling circuit is arranged in parallel at both ends of the grounding device simulation resistor R0 and the amplifying resistor R1, and the resistance compensation unit is connected to the amplifying resistor R1 through the transformer T2.

[0008] Furthermore, the resistance compensation unit includes a compensation power supply module, a voltage data acquisition module, a voltage data processing module, and a voltage control module. The specific working steps of the resistance compensation unit are as follows:

[0009] The voltage data acquisition module is used to collect the voltage data in the ground resistance measurement unit, and then transmit the collected voltage data to the voltage data processing module; the voltage data processing module is used to receive the voltage data, then calculate the shunt current, obtain the compensation voltage data, and send it to the voltage control unit. After receiving the voltage data, the voltage control unit controls the compensation power supply unit to adjust the voltage output.

[0010] Furthermore, assuming that the input voltage of the power supply device is V, after passing through the variable isolation transformer T1, the input voltage of the grounding resistance measurement unit is N1V, N1 is the transformation ratio of the variable isolation transformer T1, and the simulated resistance value of the grounding device is obtained:

[0011] , where R1 is the amplifying resistor, R2 is the protecting resistor, and V0 is the voltage sampling result of the voltage sampling circuit.

[0012] Furthermore, the voltage data processing module includes the following steps:

[0013] S1, preprocessing: performing denoising and interpolation processing on the voltage sampling results of n conduction cycles in a voltage sampling cycle of the voltage acquisition unit to generate a stable voltage value Vs;

[0014] S2, calculate the shunt current:

[0015] The current of the grounding device simulation resistor R0 is set to I1, the current through the voltage sampling circuit is set to I2, the current through the protection resistor is set to I3, and the total impedance of the sampling circuit is set to Rg. Then the magnitude of the shunt current I2 is I2= ;

[0016] S3, construct compensation algorithm: Due to the existence of the total impedance Rg of the sampling circuit, the actual voltage sampling value U of the voltage sampling circuit is U=I1*(grounding device simulation resistance R0+R1), and the compensation resistance value Rt is calculated according to the following formula:

[0017] Rt= ;

[0018] Then calculate the compensation voltage Ut of the compensation power supply:

[0019] Ut=I1*[ ],in *I2;

[0020] Calculate the compensation voltage Us output by the compensation power supply unit: , where N2 is the transformation ratio of transformer T2.

[0021] Furthermore, the specific process of denoising is as follows: a V0-t function x(t) is established based on the collected voltage data, where t is time, and the voltage data is Fourier transformed. The transformation formula is: , where f is the frequency, j is the imaginary unit, is a constant, d represents a small change; preset frequency value x, obtain the value of X(f) less than x, and then perform inverse Fourier transform on it to obtain the denoised voltage data and time function f(t). The transformation formula is , where X(f) is the frequency domain function after Fourier transform.

[0022] Furthermore, the specific process of interpolation is as follows:

[0023] Linear interpolation is performed on the denoised voltage data, and the formula is: , where f(t) is the estimated voltage at time t, t0 is the first independent variable value among the known data points, t1 is the second independent variable value among the known data points, the function value of f(t0) corresponding to t0 is the known voltage value at the independent variable value t0, the function value of f(t1) corresponding to t1 is the known voltage value at the independent variable value t1, t is the interpolation point, and the stable voltage value of the plateau period in the f(t) function is taken as Vs.

[0024] Furthermore, the switch circuit is composed of a plurality of MOS tubes.

[0025] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0026] The present invention realizes the measurement of grounding resistance under different input voltages by setting a power supply unit, a grounding resistance measuring unit and a resistance compensation unit, and accurately measures the voltage realized by collecting the output voltage for multiple times and filtering the voltage, and further reduces the measurement error by combining the collection and processing of the resistance voltage value, realizes accurate sampling of the grounding resistance voltage and reduces the interference of the circuit, and optimizes the circuit structure so that the entire grounding resistance measurement circuit has a simple structure, strong reliability, little external interference and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the overall circuit principle structure;

[0028] Figure 2 It is a module schematic diagram of the resistance compensation unit;

[0029] Figure 3 This is the program flow chart of the voltage data processing module. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field under the premise of making creative work are all within the scope of protection of the present invention.

[0031] Example:

[0032] Figure 1 As shown, the present invention provides a quality inspection system for power system installation, including a power supply unit, a ground resistance measurement unit and a resistance compensation unit. The power supply unit includes a power supply device, a switching circuit, a filter, and a variable isolation transformer T1. The input end of the filter is connected to the power supply device, the output end is connected to the variable isolation transformer T1, and the switching circuit is connected in series in the entire circuit. The input power is filtered by the filter and then transformed.

[0033] Specifically, the switch circuit is composed of a MOS tube, and the switch circuit controls its conduction and shutdown at a frequency of nHz. Therefore, in other words, a voltage sampling cycle in this embodiment includes n conduction cycles, and the average voltage value V0 finally sampled in this embodiment is calculated based on the voltage sampling results of the n conduction cycles in one cycle.

[0034] Switch circuit: The function of the switch circuit in the circuit is to connect or disconnect the current, and play the role of controlling the current on and off in the circuit. The switch controls the on and off of the current to open or close the ground resistance measurement unit, thereby controlling the operating state of the entire circuit.

[0035] The power supply unit and the ground resistance measuring unit are connected via a variable isolation transformer T1.

[0036] The variable isolation transformer T1 has a transformation ratio of N1. By using the variable isolation transformer, the voltage requirement for the power supply device can be reduced. By changing the transformation ratio of the variable isolation transformer T1, the measurement results of the grounding resistance with different input voltages can be obtained, thereby reducing the grounding resistance measurement error and improving the measurement accuracy of the grounding resistance.

[0037] Using a filter makes the input voltage of the ground resistance measurement unit more stable. The filter type is a bandpass filter.

[0038] The grounding resistance measurement unit includes a grounding device simulation resistor R0, an amplifying resistor R1, a protective resistor R2 and a voltage sampling circuit, and the voltage sampling result is V0. The grounding device simulation resistor R0, the amplifying resistor R1 and the protective resistor R2 are sequentially arranged in series, and the voltage sampling circuit is arranged in parallel at both ends of the grounding device simulation resistor R0 and the amplifying resistor R1, and is used to measure the voltage of the grounding device simulation resistor R0 and the amplifying resistor R1.

[0039] The grounding resistance voltage sampling module is specifically used to sample the voltage across the grounding device simulation resistance R0 multiple times in each conduction cycle of the test loop to obtain voltage sampling results of multiple conduction cycles, and the voltage sampling results of each conduction cycle include multiple sampled voltage values.

[0040] Assume that the input voltage of the power supply device is V. After passing through the variable isolation transformer T1, the input voltage of the ground resistance measurement unit is N1V, where N1 is the transformation ratio of the variable isolation transformer T1.

[0041] In the entire conduction loop, there are three parts of resistance, one is the grounding device simulation resistance, the simulated resistance grounding device simulation resistance R0, one is the amplifying resistance R1, and the other is the protection resistance R2. R1 is used to amplify the resistance value of the grounding device simulation resistance R0. Through the grounding resistance measurement unit, according to the voltage sampling circuit, the voltage sampling results in multiple conduction cycles are calculated according to the grounding device simulation resistance R0. According to Ohm's law, the calculation formula of the grounding device simulation resistance R0 measured by circuit analysis is:

[0042]

[0043] Since the voltage acquisition circuit is connected in parallel at both ends of the analog grounding resistance and the amplifying resistance, the voltage acquisition circuit will shunt the entire grounding resistance measurement unit, making the collected resistance value smaller. In order to improve the accuracy of grounding resistance measurement, a resistance compensation unit needs to be connected in series after the amplifying resistance.

[0044] The resistance compensation unit is connected via the transformer T2 and the amplifying resistor R1.

[0045] like Figure 2 The resistance compensation unit shown includes a compensation power supply module, a voltage data acquisition module, a voltage data processing module, and a voltage control module.

[0046] The voltage data acquisition module is used to collect voltage data in the ground resistance measurement unit and transmit the collected voltage data to the voltage data processing module.

[0047] The voltage data processing module is used to obtain the collected voltage data, and then calculate the shunt current, obtain the compensation voltage data, and send it to the voltage control unit.

[0048] The specific process of the voltage data processing module is as follows Figure 3 As shown:

[0049] It includes preprocessing, calculating shunt current, constructing compensation algorithm, and outputting compensation voltage.

[0050] S1 preprocessing: De-noise and interpolate the voltage sampling results of the voltage acquisition unit in n conduction cycles within a voltage sampling cycle. Establish the V0-t function x(t) based on the collected voltage data, where t is time. De-noising: Perform Fourier transform on the voltage data, and the transformation formula is , where f is the frequency, j is the imaginary unit, is a constant, and d represents a small change. The high-frequency noise components are eliminated in the frequency domain, and after processing, the inverse Fourier transform is performed to obtain the denoised voltage data and time function f(t). The transformation formula is , where X(f) is the frequency domain function after Fourier transform. Interpolation processing: Linear interpolation is performed on the voltage data after denoising. The formula is: , where f(t) is the estimated voltage at time t. t0 is the first independent variable value among the known data points. t1 is the second independent variable value among the known data points. The function value corresponding to f(t0) and t0 is the known voltage value at the independent variable value t0. The function value corresponding to f(t1) and t1 is the known voltage value at the independent variable value t1. t is the interpolation point, that is, the independent variable value that is expected to be interpolated or estimated between the known data points. The stable voltage value of the plateau period in the f(t) function is taken as Vs. The purpose of denoising the voltage data is to smooth the curve and remove the burrs on the voltage data curve; the purpose of interpolating the signal is to process the missing data points.

[0051] S2 calculates the shunt current: Since the voltage acquisition circuit is connected in parallel at both ends of the simulated grounding resistance and the amplifying resistance, the voltage acquisition circuit will shunt the entire grounding resistance measurement unit, making the collected grounding resistance value smaller. The current through the grounding device simulated resistance R0 is I1, the current through the voltage sampling circuit is I2, and the current through the protection resistor is I3. The total impedance of the sampling circuit is Rg. Because of the existence of Rg, the measured value of the grounding device simulated resistance R0 is smaller than the actual value. According to the pre-processed stable voltage value Vs, the shunt current I2 = .

[0052] S3 constructs compensation algorithm: Due to the existence of Rg, the actual voltage sampling value U of the voltage sampling circuit is U=I1*(grounding device simulation resistance R0+R1), and the compensation resistance value Rt is calculated according to the following formula:

[0053] Rt= ;

[0054] Then calculate the compensation voltage Ut of the compensation power supply:

[0055] Ut=I1*[ ],in *I2

[0056] Calculate the compensation power output by the compensation power supply unit, Us: , where N2 is the transformation ratio of transformer T2.

[0057] Voltage control unit: receives the voltage data processed by the voltage data processing module, and controls the voltage output of the compensation power supply unit according to the received data.

[0058] Compensation power supply unit: used to output compensation voltage data and provide compensation voltage to the grounding device simulation resistor R0 through transformer T2.

[0059] In order to make the measurement result of the grounding resistance more accurate and observe whether the grounding resistance changes under different voltages, it is necessary to change the transformation ratio N1 of the variable isolation transformer T1 and perform measurements under different input voltages.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] A variable isolation transformer is added to the power module to measure the ground resistance at different input voltages.

[0062] In order to filter the output voltage of the power supply device, a filter is further connected in series to the injection power supply device.

[0063] In order to accurately measure the voltage of the grounding resistance voltage sampling module, a switching circuit is added to reduce the measurement error by measuring the grounding resistance voltage value multiple times.

[0064] In order to accurately sample the grounding resistance voltage, an amplifier resistor is connected in series after the grounding resistance to reduce circuit interference.

[0065] By optimizing the circuit structure, the entire ground resistance measurement circuit has a simple structure, strong reliability, little external interference, and good stability.

[0066] The size of the interval and threshold is set to facilitate comparison. The size of the threshold depends on the amount of sample data and the number of bases set by technical personnel in this field for each group of sample data; as long as it does not affect the proportional relationship between the parameter and the quantized value.

[0067] The above formulas are all dimensionless and numerical calculations. The formula is a formula obtained by collecting a large amount of data and performing software simulation to obtain the most recent real situation. The preset parameters in the formula are set by technicians in this field according to actual conditions.

[0068] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A quality inspection system for power system installation, comprising a power supply unit, a ground resistance measurement unit and a resistance compensation unit, characterized in that: The power supply unit includes a power supply device, a switch circuit, a filter, and a variable isolation transformer T1. The input end of the filter is electrically connected to the power supply device, and the output end is electrically connected to the variable isolation transformer T1. The switch circuit is arranged in series between the power supply device and the variable isolation transformer T1. The power supply unit and the grounding resistance measuring unit are electrically connected through the variable isolation transformer T1. The grounding resistance measuring unit includes a grounding device simulation resistor R0, an amplifying resistor R1, a protection resistor R2 and a voltage sampling circuit. The grounding device simulation resistor R0, the amplifying resistor R1 and the protection resistor R2 are arranged in series in sequence. The voltage sampling circuit is arranged in parallel at both ends of the grounding device simulation resistor R0 and the amplifying resistor R1. The resistance compensation unit is connected to the amplifying resistor R1 through the transformer T2; The resistance compensation unit includes a compensation power supply module, a voltage data acquisition module, a voltage data processing module, and a voltage control module. The specific working steps of the resistance compensation unit are as follows: The voltage data acquisition module is used to collect the voltage data in the ground resistance measurement unit, and then transmit the collected voltage data to the voltage data processing module; the voltage data processing module is used to receive the voltage data, calculate the shunt current, obtain the compensation voltage data, and send it to the voltage control unit. After receiving the voltage data, the voltage control unit controls the compensation power supply unit to adjust the voltage output; Assume that the input voltage of the power supply device is V. After passing through the variable isolation transformer T1, the input voltage of the grounding resistance measurement unit is N1V, where N1 is the transformation ratio of the variable isolation transformer T1. The simulated resistance value of the grounding device is obtained as follows: , where R1 is the amplifying resistor, R2 is the protection resistor, and V0 is the voltage sampling result of the voltage sampling circuit; The voltage data processing module includes the following steps: S1, preprocessing: performing denoising and interpolation processing on the voltage sampling results of n conduction cycles in a voltage sampling cycle of the voltage acquisition unit to generate a stable voltage value Vs; S2, calculate the shunt current: The current of the grounding device simulation resistor R0 is set to I1, the current through the voltage sampling circuit is set to I2, the current through the protection resistor is set to I3, and the total impedance of the sampling circuit is set to Rg. Then the magnitude of the shunt current I2 is I2= ; S3, construct compensation algorithm: Due to the existence of the total impedance Rg of the sampling circuit, the actual voltage sampling value U of the voltage sampling circuit is U=I1*(grounding device simulation resistance R0+R1), and the compensation resistance value Rt is calculated according to the following formula: Rt= ; Then calculate the compensation voltage Ut of the compensation power supply: Ut=I1*[ ],in *I2; Calculate the compensation voltage Us output by the compensation power supply unit: , where N2 is the transformation ratio of transformer T2; The specific process of denoising is as follows: Based on the collected voltage data, a V0-t function x(t) is established, where t is time, and the voltage data is Fourier transformed. The transformation formula is: , where f is the frequency, j is the imaginary unit, is a constant, and d represents a small change; Preset the frequency value x, obtain the value where X(f) is less than x, and then perform inverse Fourier transform on it to obtain the denoised voltage data and time function f(t). The transformation formula is: Where X(f) is the frequency domain function after Fourier transformation; The specific process of interpolation is as follows: Linear interpolation is performed on the denoised voltage data, and the formula is: , where f(t) is the estimated voltage at time t, t0 is the first independent variable value among the known data points, t1 is the second independent variable value among the known data points, the function value of f(t0) corresponding to t0 is the known voltage value at the independent variable value t0, the function value of f(t1) corresponding to t1 is the known voltage value at the independent variable value t1, t is the interpolation point, and the stable voltage value of the plateau period in the f(t) function is taken as Vs.

2. A quality inspection system for power system installation according to claim 1, characterized in that: The switching circuit is composed of multiple MOS tubes.

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