One and two-point method: This method is suitable for small grounding devices, such as metal pipe systems, and requires that the pipe joints have not been insulated and can only measure the resistance value of a single vertical ground pole. To measure the ground resistance using the two-point method, it is necessary to ensure that the resistance of the ground electrode to be measured is much larger than the resistance of the measured current electrode. The measurement results are the sum of the resistances of the two. Power systems basically no longer use this method with high reliability and error.
The two-point method is to add an auxiliary electrode to the two-point method, which can be used to roughly measure the grounding resistance of a small grounding device. The three-point method for measuring ground resistance uses two experimental electrodes, and the two point method respectively measure the series ground resistance between the experimental electrode and the grounding device. By solving the problem, the ground resistance of the ground electrode is obtained.
3. The compensation method was gradually recognized in the 1960s. This method is mainly used to measure ground resistance. At present, IEEE/GB and other institutions and standards recommend the use of the potential drop method. However, this method requires repeated measurement and production of complex potential drop curves, which is large in workload and is inconvenient to on-site operation. In order to solve these problems, many domestic and foreign researchers have developed many derivative methods based on the potential drop method, among which the three-pole method is one of them. There are two commonly used ground resistance measurement methods in my country: 0.618 method and 30° method, which are the most commonly used methods in the three-pole method. When performing triode measurement, it is necessary to make the grounding body to be measured contact with the conductive electrode, and perform potential difference measurement, and calculate the resistance value of the grounding body to be measured through the measurement results. The measured potential difference is the potential difference between the grounding body to be measured and the auxiliary voltage pole.
In order to reduce the influence of changes in the auxiliary electrode, the measurement electrode and the electrode to be measured, the mutual inductance between the measurement wire, the stray current, and the changes in soil resistivity caused by horizontal and vertical stratification on the actual measurement results of ground resistance due to ground resistance , the researchers developed a variety of measurement methods based on the three-pole method.
4. The four-pole method adds an auxiliary voltage electrode on the basis of the three-pole method. This electrode is located near the electrode under the side, which can effectively eliminate the mutual inductance on the leads.
5. The large current method often has large currents in the grounding body, especially in the grounding networks of substations and power plants. These currents may cause errors to occur, which affects the accuracy of measurement and calculation.
In order to avoid the influence of interfering current, high current method is usually used at home and abroad to measure. This method improves the signal-to-noise ratio by passing a large current of tens of amperes into the current electrode to reduce the impact of stray current on the measurement results.
Even if the four-pole method and the high-current method can effectively eliminate interference and improve measurement accuracy, they require a large amount of power supply, generally speaking, disconnect a distribution line to power the measurement equipment. Since this affects the daily work and life of the user on the distribution line and limits the power outage time, repeated measurements become difficult to achieve.
6. Frequency conversion method In recent years, research on ground resistance measurement has been mainly focused on frequency conversion method. Compared with traditional methods, the frequency conversion method has obvious advantages. Its current injection volume and voltage are small, it has good safety, and can effectively eliminate the influence of interfering current, thereby improving the accuracy of measurement. In addition, it is easy to achieve multiple repeated measurements, eliminating the influence of accidental factors and having high measurement efficiency.