CN105606924A - Impact characteristic measurement correction method for grounding device - Google Patents

Abstract

The invention discloses a method for measuring and correcting the impact characteristics of a grounding device. The method is specifically as follows: in the first step, the grounding electrodes arranged at equal intervals around the grounding device are used as return electrodes; in the second step, the potential reference point is selected at On the return electrode; the third step is to obtain the impact grounding impedance by means of a correction coefficient, the correction coefficient is obtained based on the measured soil model, and the impact grounding impedance is measured; the present invention uses the grounding electrodes arranged at equal intervals around the grounding device as the return electrode , to ensure the uniform distribution of the grounding device to the surrounding; the present invention does not need to arrange the return electrode far away, so the test is convenient, and the impulse current generator is also easier to generate a large current; the present invention obtains the impact by means of correction coefficient Grounding impedance, the correction coefficient is calculated based on the measured soil model, while ensuring the uniform distribution of the grounding device to the surrounding flow, the more accurate measurement of the impact grounding impedance is realized.

Description

A Method for Measuring and Correcting Impulse Characteristics of Grounding Devices

technical field

The invention relates to a method for measuring and correcting a grounding device, in particular to a method for measuring and correcting the impact characteristics of a grounding device, and belongs to the technical field of high-voltage grounding testing.

Background technique

In order to meet the needs of work and safety in the power system, it is often necessary to connect some parts of the power system and its electrical equipment to the earth, which is grounding; the power system grounding can be divided into working grounding and lightning protection grounding in terms of its purpose. There are three types of grounding and protective grounding; among them, lightning protection grounding is to avoid the harm of lightning, and lightning protection equipment such as lightning rods, lightning conductors and lightning arresters must be equipped with corresponding grounding devices to guide lightning current into the earth; due to the wide distribution of transmission lines in power systems , the most vulnerable to lightning strikes, and the lightning current of the transmission line is introduced into the earth through the grounding device of the tower. The operation experience at home and abroad shows that effectively reducing the grounding resistance of the tower is the most effective measure to improve the protection effect of direct lightning strikes on the transmission line. In the design of line towers, the value of the impact grounding resistance of the line tower grounding device directly affects the lightning protection effect of the line. For towers of general height, reducing the impact grounding resistance of towers is an effective measure to improve the lightning resistance level of lines and reduce the tripping rate due to lightning strikes. In order to ensure the lightning protection effect of the transmission line, it is necessary to regularly measure the grounding status of the tower; at present, the power frequency grounding resistance of the tower grounding is usually used to evaluate the grounding status of the tower; the power frequency grounding resistance of the tower grounding is mainly used for discharge work frequency short-circuit current, and the impact characteristics of the grounding device determine the lightning protection effect of the transmission line of the power system; due to the effect of longitudinal inductance, the grounding device only has a limited area to work under the impact, which is different from the grounding resistance and floor area at power frequency The square root of is not consistent, so the impact grounding state of the tower cannot be correctly evaluated by measuring the power frequency grounding resistance of the tower ground. The impulse characteristics of the tower grounding device can be tested by using the impulse current generator, but the current test method mainly follows the three-pole method of the power frequency grounding resistance test. Due to the fact that the return pole of the current under the three-pole method is concentrated in one place, and the impulse current contains a large number of high-frequency components, the current distribution on the grounding device is uneven when measuring the impulse characteristics of the grounding device according to the three-pole method, which is different from the actual situation. The difference is large; different from the power frequency, the characteristics of the grounding device under impact are greatly affected by the current distribution of the grounding device; especially under high impact current, the soil will discharge, which is closely related to the current distribution on the grounding device relevant. Since the discharge is nonlinear, it is necessary to ensure that the current distribution on the grounding device is consistent with the actual situation when testing the impact characteristics of the tower grounding device. In order to achieve this purpose, some research units have used the metal ring surrounding the grounding device under test as the current return pole. Using the metal ring as the current return electrode ensures that the grounding device has a uniform current flow in all directions, but because the metal ring is very close to the grounding device under test, the reverse potential generated on the grounding device is very large, which greatly offsets the The potential of the grounding device causes the test result to be much smaller than the actual value. Theoretical analysis shows that after using the metal ring as the current return electrode, only when the metal ring is infinitely large, the test result is the same as the actual one, otherwise even if the ring is used as the potential reference point, the test result is too small, and the smaller the ring , the smaller it is; because it is difficult to use a large ring in reality, the return electrode group surrounding the grounding device is actually used as the return electrode, but the rest of the return ring is the same, and the above problems still exist, so further improvement is needed.

Contents of the invention

(1) Technical problems to be solved

In order to solve the above problems, the present invention proposes a method for measuring and correcting the impact characteristics of the grounding device. The correction coefficient is obtained based on the measured soil model, which ensures the uniform distribution of the grounding device to the surroundings, and realizes the shock grounding impedance. more accurate measurement.

(2) Technical solution

The method for measuring and correcting the impact characteristics of the grounding device of the present invention is specifically as follows:

The first step is to use the grounding electrodes arranged at equal intervals around the grounding device as the return electrode;

In the second step, select the potential reference point on the return electrode;

In the third step, the impact grounding impedance is obtained by means of a correction coefficient, which is calculated based on the measured soil model, and the impact grounding impedance is measured.

Further, the first step to the third step are specifically as follows:

In the first step, the apparent resistivity of the soil near the grounding device is tested by the four-pole method;

In the second step, a layered model of soil resistivity is obtained based on the measured apparent resistivity of the soil;

The third step is to collect the data of the grounding device under test;

The fourth step is to arrange 8 return electrodes at equal intervals around the grounding device, each electrode is 0.6-0.8m deep into the ground, and has good contact with the soil, and uses insulated wires to equipotentially connect the 8 return electrodes;

The fifth step is to use a large current impulse generator to inject an impulse current between the grounding device under test and the eight return poles, and measure the current waveform into the ground;

The sixth step is to measure the voltage waveform of the grounding device with the 8 return electrodes as potential reference points;

The seventh step is to find the ratio of the peak value of the voltage waveform to the peak value of the current waveform as the apparent impact grounding impedance of the grounding device;

The eighth step, based on the ground current waveform measured in the fifth step, simulate the impact grounding resistance test results of the grounding device under test in the layered soil model with 8 return electrodes as potential reference points;

In the ninth step, based on the ground current waveform measured in the fifth step, ignoring the existence of 8 return electrodes, simulate the impact grounding of the measured grounding device in the layered soil model with infinity as the potential reference point Resistance test results;

In the tenth step, calculate the ratio of the calculation result in the eighth step to the calculation result in the ninth step, and multiply the ratio by the apparent impact grounding impedance measured in the seventh step to obtain the final impact grounding impedance.

(3) Beneficial effects

Compared with the prior art, the method for measuring and correcting the impact characteristics of the grounding device of the present invention has the following advantages:

The present invention uses the grounding electrodes arranged at equal intervals around the grounding device as the return electrodes, which ensures the uniform distribution of the grounding device to the surroundings; the present invention does not need to arrange the return electrodes far away, so the test is convenient, and the impact current occurs at the same time. It is also easier to generate a large current; the present invention selects the potential reference point on the return electrode, which minimizes the direct error generated by the test; the present invention obtains the impact grounding impedance by means of a correction coefficient, and the correction coefficient is based on the actual measured soil The model is used to find out that while ensuring the uniform distribution of the grounding device to the surrounding flow, the more accurate measurement of the impact grounding impedance is realized.

Description of drawings

Fig. 1 is a schematic diagram of arrangement of return electrodes in Embodiment 1 of the present invention;

FIG. 2 is a schematic diagram of correction coefficients of the impulse grounding impedance test in Embodiment 1 of the present invention.

detailed description

The method for measuring and correcting the impact characteristics of the grounding device of the present invention is specifically as follows:

The first step is to use the grounding electrodes arranged at equal intervals around the grounding device as the return electrode;

In the second step, select the potential reference point on the return electrode;

In the third step, the impact grounding impedance is obtained by means of a correction coefficient, which is calculated based on the measured soil model, and the impact grounding impedance is measured.

Wherein, described method is specifically as follows:

In the first step, the apparent resistivity of the soil near the grounding device is tested by the four-pole method;

In the second step, a layered model of soil resistivity is obtained based on the measured apparent resistivity of the soil;

The third step is to collect the data of the grounding device under test;

The fourth step is to arrange 8 return electrodes at equal intervals around the grounding device, each electrode is 0.6-0.8m deep into the ground, and has good contact with the soil, and uses insulated wires to equipotentially connect the 8 return electrodes;

The fifth step is to use a large current impulse generator to inject an impulse current between the grounding device under test and the eight return poles, and measure the current waveform into the ground;

The sixth step is to measure the voltage waveform of the grounding device with the 8 return electrodes as potential reference points;

The seventh step is to find the ratio of the peak value of the voltage waveform to the peak value of the current waveform as the apparent impact grounding impedance of the grounding device;

The eighth step, based on the ground current waveform measured in the fifth step, simulate the impact grounding resistance test results of the grounding device under test in the layered soil model with 8 return electrodes as potential reference points;

In the ninth step, based on the ground current waveform measured in the fifth step, ignoring the existence of 8 return electrodes, simulate the impact grounding of the measured grounding device in the layered soil model with infinity as the potential reference point Resistance test results;

In the tenth step, calculate the ratio of the calculation result in the eighth step to the calculation result in the ninth step, and multiply the ratio by the apparent impact grounding impedance measured in the seventh step to obtain the final impact grounding impedance.

Example 1:

As shown in Figure 1, in the 40 ohm uniform soil, there are three tested cross-type grounding devices buried, and the elongation poles are 5, 10, and 15 m respectively. Eight return poles are arranged at equal intervals on a circle with a radius of 20m, and the correction coefficient of the impact grounding impedance test shown in Figure 2 is obtained.

The above-mentioned embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the concept and scope of the present invention. Under the premise of not departing from the design concept of the present invention, various modifications and improvements made by ordinary persons in the art to the technical solution of the present invention shall fall within the scope of protection of the present invention, and the technical content claimed in the present invention has been fully described in the claims.

Claims (2)

1. A grounding device impact characteristic measurement and correction method is characterized in that, the method is as follows: The first step is to use the grounding electrodes arranged at equal intervals around the grounding device as the return electrode; In the second step, select the potential reference point on the return electrode; In the third step, the impact grounding impedance is obtained by means of a correction coefficient, which is calculated based on the measured soil model, and the impact grounding impedance is measured. 2. The method for measuring and correcting the impact characteristics of the grounding device according to claim 1, wherein the first step to the third step are specifically as follows: In the first step, the apparent resistivity of the soil near the grounding device is tested by the four-pole method; In the second step, a layered model of soil resistivity is obtained based on the measured apparent resistivity of the soil; The third step is to collect the data of the grounding device under test; The fourth step is to arrange 8 return electrodes at equal intervals around the grounding device, each electrode is 0.6-0.8m deep into the ground, and has good contact with the soil, and uses insulated wires to equipotentially connect the 8 return electrodes; The fifth step is to use a large current impulse generator to inject an impulse current between the grounding device under test and the eight return poles, and measure the current waveform into the ground; The sixth step is to measure the voltage waveform of the grounding device with the 8 return electrodes as potential reference points; The seventh step is to find the ratio of the peak value of the voltage waveform to the peak value of the current waveform as the apparent impact grounding impedance of the grounding device; The eighth step, based on the ground current waveform measured in the fifth step, simulate the impact grounding resistance test results of the grounding device under test in the layered soil model with 8 return electrodes as potential reference points; In the ninth step, based on the ground current waveform measured in the fifth step, ignoring the existence of 8 return electrodes, simulate the impact grounding of the measured grounding device in the layered soil model with infinity as the potential reference point Resistance test results; In the tenth step, calculate the ratio of the calculation result in the eighth step to the calculation result in the ninth step, and multiply the ratio by the apparent impact grounding impedance measured in the seventh step to obtain the final impact grounding impedance.