A transmission tower grounding resistance value measurement system and measurement method based on multi-frequency measurement

Abstract

The invention discloses a transmission tower grounding resistance value measurement system and a measurement method based on multi-frequency measurement, which relate to the technical field of lightning protection and grounding of electric power systems. The system is composed of a power supply module, an MCU main control unit, a sinusoidal voltage generation circuit module, a current detection circuit module and a phase detection circuit module; the power supply module supplies power to the entire system; the sinusoidal voltage generation circuit module is composed of a DDS signal generation module, a drive circuit and a voltage transformer; the current detection circuit module is composed of a current transformer, a high-precision resistor and a filter module; the phase detection circuit module detects the phase difference between voltage and current; the transmission tower grounding resistance value measurement method based on multi-frequency measurement of the invention can obtain a plurality of measurement data by multi-frequency measurement, and adopt a weighted average method to calculate according to the influence of each frequency on the discharge of a transmission line, so as to obtain the final grounding resistance value, and the data is more accurate and the measurement result is more meaningful.

Description

Technical Field

[0001] The invention relates to the technical field of lightning protection and grounding of electric power systems, in particular to a transmission tower grounding resistance value measurement system and a measurement method based on multi-frequency measurement. Background Art

[0002] Lightning protection technology for transmission lines is the key to the safe operation of power grid systems. Accurately measuring the grounding resistance of transmission line towers is of great significance for lightning protection of transmission lines and is related to the safe and stable operation of transmission lines. At present, the grounding inspection and maintenance of power lines relies on workers to measure the grounding resistance. The existing workers use the three-pole method and the clamp meter method to measure the grounding resistance. Among them, the three-pole method is a traditional grounding resistance measurement method with high measurement accuracy and is suitable for the measurement of various grounding devices. However, this method must disconnect the grounding body from the grounding electrode during measurement. The clamp meter method uses a non-contact measurement method. Its advantage is that there is no need to arrange current electrodes and voltage electrodes during measurement. As long as the clamp meter is clamped on the grounding lead of the line tower, the grounding resistance can be measured.

[0003] The measurement principle of the clamp meter is to use the ratio of voltage to current to measure the grounding resistance of the tower. Therefore, its measurement accuracy depends on the accuracy of the voltage transformer sensing the tower voltage and the accuracy of the current measured by the current transformer. The general clamp meter functions are relatively simple, and no in-depth research has been conducted on the issue of improving the accuracy of the above two circuits. Since the voltage and current measurement accuracy is not high, and the measured resistance value is the ratio of voltage to current, and the influence of the AC phase is not taken into account, the measured grounding resistance value deviates greatly from the actual resistance value. At present, there are two problems with the clamp meter measuring the tower grounding resistance:

[0004] First, during the measurement, only the ratio of voltage to current was measured without considering the phase factor, and the phase of AC voltage and current is a very important technical parameter; second, the clamp meter used to measure the grounding resistance of the transmission line did not consider the discharge interference factor, and the discharge interference of the transmission line will obviously affect the measurement accuracy.

[0005] Therefore, it is urgent to study a method for measuring the grounding resistance of transmission towers with high measurement accuracy to ensure the lightning protection performance and safe and stable operation of transmission lines. Summary of the invention

[0006] To solve the above problems, the purpose of the present invention is to provide a transmission tower grounding resistance value measurement system and measurement method based on multi-frequency measurement, which is based on the clamp meter method, adopts multi-frequency measurement, fully considers the phase relationship between voltage and current, and considers the influencing factors of transmission line discharge interference, thereby improving the measurement accuracy of the transmission line tower grounding resistance and ensuring the lightning protection performance and safe and stable operation of the transmission line.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] A transmission tower grounding resistance measurement system based on multi-frequency measurement, which consists of a power supply module, an MCU main control unit, a sinusoidal voltage generation circuit module, a current detection circuit module and a phase detection circuit module;

[0009] The power module supplies power to the entire system;

[0010] The MCU main control unit is used to control the DDS module to generate multi-frequency sine wave signals and adjust the output amplitude and initial phase on the one hand; on the other hand, it uses its built-in AD module to directly measure data and obtain current values; and finally obtains the resistance data of the measured object through calculation;

[0011] The sinusoidal voltage generation circuit module is composed of a DDS signal generation module, a drive circuit and a voltage transformer; the DDS signal generation module is programmed by a DDS chip to achieve sinusoidal wave output, and its output frequency, amplitude and phase are all controlled by MCU programming, and the drive circuit is used to increase the output power, thereby driving the voltage transformer output;

[0012] The current detection circuit module is composed of a current transformer, a high-precision resistor and a filter module. When measuring the ground loop resistance value, the current data is read back through the current transformer and converted into a voltage value through a high-precision resistor. The filter module is used to filter the interference around the tower. The filtered signal is directly sent to the MCU, and the value is read by the AD module.

[0013] The phase detection circuit module detects the phase difference between voltage and current.

[0014] Preferably, the MCU main control unit is an MSP430 single chip microcomputer.

[0015] Preferably, the DDS signal generating module is an AD9850 module.

[0016] Preferably, the current signal and the voltage signal of the phase detection circuit module are both formed into a square wave shaping circuit by an OP07 operational amplifier, and the phase is captured by the MCU.

[0017] Preferably, the current detection circuit module uses ADG708 as an 8-to-1 mode switch, and directly sends the current to the AD port of the single-chip microcomputer after filtering.

[0018] Preferably, the power supply module provides 3.3V voltage for the MCU main control unit, and provides ±5V or ±15V voltage for the current detection circuit module, the sinusoidal voltage generation circuit module and the phase detection circuit module.

[0019] The present invention also includes a method for measuring the grounding resistance of a transmission tower based on multi-frequency measurement, comprising the following steps:

[0020] Step 1: No voltage is applied to the voltage transformer, and the current transformer reads the current I of the tower grounding down conductor at N frequencies. i , (i=1, 2...N), this current is the induced discharge current of the transmission line tower, which is the interference current in the general measurement process;

[0021] Step 2: Remove 10% to 20% of the data with larger values ​​measured in step 1, and determine the weighted value q for the remaining M data. i , the specific formula is as follows:

[0022]

[0023] Among them I j To read the current of the tower grounding down conductor at M frequencies;

[0024] In the weighted value q i In the formula, the larger the measured current value is, the smaller the weighted value is, and the sum of the weighted values ​​of M data is 1;

[0025] Step 3: According to the working principle of the loop method, measure the loop resistance |Z at M frequencies i |, where i=1, 2...M, calculate the grounding resistance value of the measured tower ;

[0026] Step 4: According to the working principle of phase difference measurement, measure the phase difference φ at each frequency i , i=1, 2...M, and then use the phase difference and |Z i | Calculate R i , the formula is as follows:

[0027] ;

[0028] Step 5: Weighted average The value is as follows:

[0029] .

[0030] Preferably, the specific process of step three is as follows:

[0031] set up is the grounding resistance value of the measured tower, are the grounding resistance values ​​of the remaining towers respectively;

[0032] When the voltage is applied to the grounding device of the tower under test by the clamp meter method and the induced current is measured, the loop resistance R loop The calculation formula is as follows:

[0033] ;

[0034] In general, if the grounding resistance values ​​of other towers are qualified, , that is, the loop resistance is the grounding resistance value of the measured tower, but the data error of this processing method may be large, so the following processing method is adopted;

[0035] Since the transmission line is inductive and there is an equivalent capacitance between it and the earth, the loop resistance R loop The equivalent circuit resistance Z loop It means that the calculation formula is

[0036] ;

[0037] Where f is the measurement frequency, ω is the angular frequency of the measurement signal, and ; L is the equivalent inductance of the overhead ground wire of the transmission line, ; C is the equivalent capacitance of overhead ground wire of transmission line to ground; X C is the equivalent capacitive reactance of the overhead ground wire of the transmission line to the ground, ;

[0038] For a specific frequency, the loop resistance Z loop That is |Z|. M frequencies are used to measure the circuit under test, and M Z values ​​are obtained, which are recorded as |Z i |, i=1, 2…M.

[0039] Preferably, in step 4, according to the phase difference measurement working principle, the phase difference φ is measured at each frequency i , where i=1, 2...M, the specific steps are as follows:

[0040] Step 4.1, using a zero-crossing comparator, convert the voltage and current sinusoidal signals into square waves respectively, and the two paths use circuits with exactly the same parameters;

[0041] Step 4.2: Use the microcontroller to collect the rising edge time t of the voltage signal u and the current signal rising edge time t i ;

[0042] Step 4.3, if the current measurement frequency is f, then its period T is 1 / f, and the phase difference is

[0043] .

[0044] Preferably, the measurement frequency f is 50-5000 Hz.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] The invention discloses a transmission tower grounding resistance measurement system based on multi-frequency measurement. Based on the loop method, a clamp meter is used to measure the loop resistance value by adopting multi-frequency, thereby overcoming the factor that single frequency measurement is affected by the induced current of the transmission line. Before the measurement, the frequency spectrum distribution of the discharge current of the transmission line is first measured, thereby avoiding the discharge interference of the transmission line as much as possible. A programmable DDS signal generation chip is used, and the automatic adjustment and control of the frequency can be realized through single-chip microcomputer programming.

[0047] The invention discloses a transmission tower grounding resistance measurement method based on multi-frequency measurement, which can obtain a plurality of measurement data by multi-frequency measurement, and adopt a weighted average method to calculate the final grounding resistance value according to the influence of each frequency on the discharge of the transmission line; on the one hand, during data processing, several frequencies with the largest interference are removed, and other frequencies are calculated by weighted average according to the interference conditions, thereby improving the measurement accuracy; on the other hand, the influence of the inductive factor of the overhead ground wire of the transmission line and the equivalent capacitance between the earth is fully considered, and multi-frequency multiple measurements are adopted to form a specific calculation formula to solve the resistance value, so that the data is more accurate and the measurement result is more meaningful. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the composition of the transmission tower grounding resistance value measurement system for multi-frequency measurement;

[0049] Figure 2 Circuit diagram for sinusoidal voltage generation;

[0050] Figure 3 is a phase detection circuit diagram;

[0051] Figure 4 is the current detection circuit diagram;

[0052] Figure 5 It is the equivalent model diagram of the grounding system;

[0053] Figure 6 This is the equivalent circuit model diagram considering inductance and capacitance. DETAILED DESCRIPTION

[0054] The object of the present invention is to provide a transmission tower grounding resistance value measurement system and measurement method based on multi-frequency measurement. The present invention is further described below in conjunction with specific embodiments.

[0055] Example 1

[0056] A transmission tower ground resistance measurement system based on multi-frequency measurement, such as Figure 1As shown, it is composed of a power module, an MCU main control unit, a sinusoidal voltage generating circuit module, a current detection circuit module and a phase detection circuit module; the power module supplies power to the entire system; the MCU main control unit provides a 3.3V voltage, and provides ±5V or ±15V voltage for the current detection circuit module, the sinusoidal voltage generating circuit module and the phase detection circuit module; the size of the voltage provided is determined by the requirements of the chip.

[0057] The MCU main control unit is used to control the DDS module to generate multi-frequency sine wave signals and adjust the output amplitude and initial phase on the one hand; on the other hand, it uses its built-in AD module to directly measure data and obtain current values; and finally obtains the resistance data of the measured object through calculation;

[0058] The sinusoidal voltage generation circuit module is composed of a DDS signal generation module, a drive circuit and a voltage transformer; the DDS signal generation module is programmed by a DDS chip to achieve sinusoidal wave output, and its output frequency, amplitude and phase are all controlled by MCU programming, and the drive circuit is used to increase the output power, thereby driving the voltage transformer output;

[0059] The current detection circuit module is composed of a current transformer, a high-precision resistor and a filter module. When measuring the ground loop resistance value, the current data is read back through the current transformer and converted into a voltage value through a high-precision resistor. The filter module is used to filter the interference around the tower. The filtered signal is directly sent to the MCU, and the value is read by the AD module.

[0060] The phase detection circuit module detects the phase difference between voltage and current;

[0061] The MCU main control unit of this embodiment is preferably an MSP430 single-chip microcomputer, which has a low power consumption mode, a phase capture function, and a built-in AD module.

[0062] The circuit diagram of the sinusoidal voltage generating circuit module of this embodiment is as follows: Figure 2 As shown, the DDS signal generation module is preferably an AD9850 module, wherein the AD9850 has a 40-bit control word, 32 bits for frequency control, 5 bits for phase control, 1 bit for power control, and 2 bits for selecting the working mode. The 40-bit control word can be input to the AD9850 in parallel or serial mode, and its serial data format is shown in Table 1:

[0063] Table 1 Serial control word format of AD9850 module

[0064]

[0065] In Table 1, the output frequency of AD9850 should satisfy the following formula:

[0066]

[0067] Where W is the frequency control word, is the clock frequency of the AD9850 module. The clock crystal of the AD9850 module used in this design is 125MHz. The calculation formula of the frequency control word is:

[0068]

[0069] The relationship between the phase control word and the phase is shown in Table 2:

[0070] Table 2 Relationship between phase control word and phase

[0071]

[0072] The current signal and voltage signal of the phase detection circuit module of this embodiment are both square wave shaped by the OP07 operational amplifier, and the phase is captured by the MCU. The phase detection circuit diagram is shown in FIG. Figure 3 shown.

[0073] The current detection circuit module of this embodiment uses ADG708 as an 8-to-1 mode switch, and directly sends it to the AD port of the single-chip microcomputer after filtering. The circuit diagram is as follows Figure 4 shown.

[0074] Example 2

[0075] A method for measuring the grounding resistance of a transmission tower based on multi-frequency measurement comprises the following steps:

[0076] Step 1: No voltage is applied to the voltage transformer, and the current transformer reads the current I of the tower grounding down conductor at N frequencies. i , (i=1, 2...N), this current is the induced discharge current of the transmission line tower, which is the interference current in the general measurement process;

[0077] Step 2: Remove 10% to 20% of the data with larger values ​​measured in step 1, and determine the weighted value q for the remaining M data. i , the specific formula is as follows:

[0078]

[0079] Among them I j To read the current of the tower grounding down conductor at M frequencies;

[0080] In the weighted value q i In the formula, the larger the measured current value is, the smaller the weighted value is, and the sum of the weighted values ​​of M data is 1;

[0081] Step 3: According to the working principle of loop method measurement, the equivalent model of the grounding system is as follows: Figure 5 As shown, the loop resistance |Z is measured at M frequencies i |, where i=1, 2...M, calculate the grounding resistance value of the measured tower ; The specific process is as follows:

[0082] set up is the grounding resistance value of the measured tower, are the grounding resistance values ​​of the remaining towers respectively;

[0083] When the voltage is applied to the grounding device of the tower under test by the clamp meter method and the induced current is measured, the loop resistance R loop The calculation formula is as follows:

[0084] ;

[0085] In general, if the grounding resistance values ​​of other towers are qualified, , that is, the loop resistance is the grounding resistance of the measured tower. However, since the transmission line is inductive and there is an equivalent capacitance between it and the earth, the equivalent loop circuit model is as follows: Figure 6 As shown, the error of this algorithm may be large; the loop resistance R loop The equivalent circuit resistance Z loop It means that the calculation formula is

[0086] ;

[0087] Wherein, f is the measurement frequency, preferably in the range of 50~5000Hz; ω is the angular frequency of the measurement signal, and ; L is the equivalent inductance of the overhead ground wire of the transmission line, ; C is the equivalent capacitance of overhead ground wire of transmission line to ground; X C is the equivalent capacitive reactance of the overhead ground wire of the transmission line to the ground, ;

[0088] For a specific frequency, the loop resistance Z loop That is |Z|. M frequencies are used to measure the circuit under test, and M Z values ​​are obtained, which are recorded as |Z i |, i=1, 2…M.

[0089] Step 4: First, according to the working principle of phase difference measurement, measure the phase difference φ at each frequency. i , where i=1, 2...M, the specific steps are as follows:

[0090] Step 4.1, using a zero-crossing comparator, convert the voltage and current sinusoidal signals into square waves respectively, and the two paths use circuits with exactly the same parameters;

[0091] Step 4.2: Use the microcontroller to collect the rising edge time t of the voltage signal u and the current signal rising edge time t i ;

[0092] Step 4.3, if the current measurement frequency is f, then its period T is 1 / f, and the phase difference φ i That is

[0093] ;

[0094] Then, using the phase difference and |Z i | Calculate R i , the formula is as follows:

[0095] ;

[0096] Step 5: Weighted average to find R g The value is as follows:

[0097] .

[0098] Example 3

[0099] A method for measuring the grounding resistance of a transmission tower based on multi-frequency measurement comprises the following steps:

[0100] Step 1: No voltage is applied to the voltage transformer, and the current transformer reads the current I of the tower grounding down conductor at 8 frequencies. i , (i=1, 2...8), this current is the induced discharge current of the transmission line tower, which is the interference current in the general measurement process; the results are shown in Table 3;

[0101] Step 2: Remove 20% of the data with larger values ​​measured in step 1. In this embodiment, I1 and I6 are removed from the data, and the remaining 6 data are used to determine the weighted value q. i , the specific formula is as follows:

[0102]

[0103] Among them I j To read the current of the tower grounding down conductor at 6 frequencies;

[0104] In the weighted value q i In the formula, the larger the measured current value, the smaller the weighted value, and the sum of the weighted values ​​of the 6 data is 1; q i The results are shown in Table 3.

[0105] Step 3: According to the working principle of the loop method, measure the loop resistance |Z at 6 frequencies i|, where i=1, 2...6, calculate the grounding resistance value of the measured tower ; The specific process is as follows:

[0106] set up is the grounding resistance value of the measured tower, are the grounding resistance values ​​of the remaining towers respectively;

[0107] When the voltage is applied to the grounding device of the tower under test by the clamp meter method and the induced current is measured, the loop resistance R loop The calculation formula is as follows:

[0108] ;

[0109] If the grounding resistance values ​​of other towers are qualified, , that is, the loop resistance is the grounding resistance value of the measured tower. The error of this algorithm may be large; but since the transmission line is inductive and there is an equivalent capacitance between it and the earth, the loop resistance R loop The equivalent circuit resistance Z loop It means that the calculation formula is

[0110] ;

[0111] Wherein, f is the measurement frequency, preferably in the range of 50~5000Hz; ω is the angular frequency of the measurement signal, and ; L is the equivalent inductance of the overhead ground wire of the transmission line, ; C is the equivalent capacitance of overhead ground wire of transmission line to ground; X C is the equivalent capacitive reactance of the overhead ground wire of the transmission line to the ground, ;

[0112] For a specific frequency, the loop resistance Z loop That is |Z|. M frequencies are used to measure the circuit under test, and M Z values ​​are obtained, which are recorded as |Z i |, i=1, 2…6, the results are shown in Table 3.

[0113] Step 4: First, according to the working principle of phase difference measurement, measure the phase difference φ at each frequency. i , where i=1, 2...6, the specific steps are as follows:

[0114] Step 4.1, using a zero-crossing comparator, convert the voltage and current sinusoidal signals into square waves respectively, and the two paths use circuits with exactly the same parameters;

[0115] Step 4.2: Use the microcontroller to collect the rising edge time t of the voltage signal u and the current signal rising edge time t i ;

[0116] Step 4.3, if the current measurement frequency is f, then its period T is 1 / f, and the phase difference φ i That is

[0117] ; Phase difference φ i The results are shown in Table 3;

[0118] Then, using the phase difference and |Z i | Calculate R i , the formula is as follows:

[0119] ; R i The results are shown in Table 3;

[0120] Step 5: Weighted average to find R g The value is as follows:

[0121] ; R g The results are shown in Table 3.

[0122] Table 3 Actual detected data and processed data results

[0123]

[0124] It can be seen from the results in Table 1 that the data |Z1|~|Z8| measured by the existing loop method is the loop resistance, which is also considered to be the grounding resistance of the measured tower. There is a large gap between the R value obtained by this method and the value, and it is greatly affected by the measurement frequency. The present invention fully considers the influence of the inductive factor of the overhead ground wire of the transmission line and the equivalent capacitance between the earth, adopts multi-frequency and multiple measurements, forms a specific calculation formula to solve the resistance value, and the data is more accurate.

Claims

1. A transmission tower ground resistance measurement system based on multi-frequency measurement, characterized in that: It consists of a power supply module, an MCU main control unit, a sinusoidal voltage generation circuit module, a current detection circuit module and a phase detection circuit module; the power supply module supplies power to the entire system; The MCU main control unit is used to control the DDS module to generate multi-frequency sine wave signals and adjust the output amplitude and initial phase on the one hand; on the other hand, it uses its built-in AD module to directly measure data and obtain current values; and finally obtains the resistance data of the measured object through calculation; The sinusoidal voltage generation circuit module is composed of a DDS signal generation module, a drive circuit and a voltage transformer; the DDS signal generation module is programmed by a DDS chip to achieve sinusoidal wave output, and its output frequency, amplitude and phase are all controlled by MCU programming, and the drive circuit is used to increase the output power, thereby driving the voltage transformer output; The current detection circuit module is composed of a current transformer, a high-precision resistor and a filter module. When measuring the ground loop resistance value, the current data is read back through the current transformer and converted into a voltage value through a high-precision resistor. The filter module is used to filter the interference around the tower. The filtered signal is directly sent to the MCU, and the value is read by the AD module. The phase detection circuit module detects the phase difference between voltage and current.

2. The transmission tower ground resistance measurement system based on multi-frequency measurement according to claim 1, characterized in that: The MCU main control unit is an MSP430 single chip microcomputer.

3. The transmission tower ground resistance measurement system based on multi-frequency measurement according to claim 1, characterized in that: The DDS signal generating module is an AD9850 module.

4. The transmission tower ground resistance measurement system based on multi-frequency measurement according to claim 1, characterized in that: The current signal and voltage signal of the phase detection circuit module are both formed into a square wave shaping circuit by an OP07 operational amplifier, and the phase is captured by the MCU.

5. The transmission tower ground resistance measurement system based on multi-frequency measurement according to claim 1, characterized in that: The current detection circuit module uses ADG708 as an 8-to-1 mode switch, and directly sends the current to the AD port of the single-chip microcomputer after filtering.

6. The transmission tower ground resistance measurement system based on multi-frequency measurement according to claim 1, characterized in that: The power supply module provides 3.3V voltage for the MCU main control unit, and provides ±5V or ±15V voltage for the current detection circuit module, the sinusoidal voltage generation circuit module and the phase detection circuit module.

7. A method for measuring the ground resistance of a transmission tower based on multi-frequency measurement, characterized in that: The following steps are involved: Step 1: No voltage is applied to the voltage transformer, and the current transformer reads the current I of the tower grounding down conductor at N frequencies. i , i=1, 2...N, this current is the induced discharge current of the transmission line tower, which is the interference current in the general measurement process; Step 2: Remove 10% to 20% of the data with larger values ​​measured in step 1, and determine the weighted value q for the remaining M data. i , the specific formula is as follows: ； Among them I j To read the current of the tower grounding down conductor at M frequencies; Step 3: According to the working principle of the loop method, measure the loop resistance |Z at M frequencies i |, where i=1, 2...M, calculate the grounding resistance value of the measured tower ; Step 4: According to the working principle of phase difference measurement, measure the phase difference φ at each frequency i , i=1, 2...M, and then use the phase difference and |Z i | Calculate R i , the formula is as follows: ； Step 5: Weighted average to find R g The value is as follows: 。 8. The method for measuring the grounding resistance of a transmission tower based on multi-frequency measurement according to claim 7, characterized in that: The specific process of step three is as follows: set up is the grounding resistance value of the measured tower, are the grounding resistance values ​​of the remaining towers respectively; When the voltage is applied to the grounding device of the tower under test by the clamp meter method and the induced current is measured, the loop resistance R loop The calculation formula is as follows: ； However, since the transmission line is inductive and there is an equivalent capacitance between it and the earth, the loop resistance R loop The equivalent circuit resistance Z loop It means that the calculation formula is ； Where f is the measurement frequency, ω is the angular frequency of the measurement signal, and ; L is the equivalent inductance of the overhead ground wire of the transmission line, ; C is the equivalent capacitance of overhead ground wire of transmission line to ground; X C is the equivalent capacitive reactance of the overhead ground wire of the transmission line to the ground, ; For a specific frequency, the loop resistance Z loop That is |Z|. M frequencies are used to measure the circuit under test, and M Z values ​​are obtained, which are recorded as |Z i |, i=1, 2…M.

9. The method for measuring the grounding resistance of a transmission tower based on multi-frequency measurement according to claim 7, characterized in that: In step 4, according to the working principle of phase difference measurement, the phase difference φ is measured at each frequency. i , where i=1, 2...M, the specific steps are as follows: Step 4.1, using a zero-crossing comparator, convert the voltage and current sinusoidal signals into square waves respectively, and the two paths use circuits with exactly the same parameters; Step 4.2: Use the microcontroller to collect the rising edge time t of the voltage signal u and the current signal rising edge time t i ; Step 4.3, if the current measurement frequency is f, then its period T is 1 / f, and the phase difference is 。 10. The method for measuring the grounding resistance of a transmission tower based on multi-frequency measurement according to claim 8, characterized in that: The measurement frequency f is between 50 and 5000 Hz.

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