Analysis of Factors Affecting Ground Resistance Measurement Results

     The article systematically analyzes the influence of various factors on the ground resistance measurement results, such as the position of measuring electrodes, uneven soil resistivity, mutual inductance between leads, metal objects near the underground, internal resistance of the voltmeter, skin effect of the earth, physical properties of the measuring electrodes themselves and interference signals, which has certain guiding significance for the correct measurement of ground resistance values.

　　The grounding resistance value is an important technical indicator of the grounding system. It is an important parameter to measure the effectiveness and safety of the grounding system and to identify whether the grounding system meets the design requirements. The measurement methods recommended in the current regulations are mostly based on ideal conditions such as uniform soil, ignoring the mutual inductance between the measurement leads, ignoring the internal resistance of the voltmeter, and the shape of the grounding electrode being hemispherical. However, in the actual measurement process, the grounding resistance results are often affected by multiple factors, resulting in a certain difference between the measured value of the grounding resistance and the true value. This article systematically summarizes and analyzes the relationship between the grounding resistance measurement results and various influencing factors, which has certain guiding significance for the correct measurement of the grounding resistance value.

　　Measuring electrode position

　　When measuring ground resistance using the three-pole method, there is a potential electrode position that can obtain the true ground resistance value of the ground electrode to be measured. This position is called the potential electrode compensation point. The so-called compensation is to compensate for the reduction in ground impedance caused by the current electrode being close to the ground electrode system.

　　Taking the measurement of grounding resistance by the linear compensation method and the triangular compensation method as an example, as shown in Figure 1, when the positions of point E and point C are fixed, the thick solid line is the position trajectory of the voltage pole C compensation point. As long as the voltage pole C is located on this curve, the true grounding resistance value can be measured. It can be concluded that:

　　1) If the voltage pole is outside the curve, the measured ground resistance value is smaller than the actual ground resistance value.

　　2) If the voltage pole point P is on the curve, the measured ground resistance value is equal to the actual ground resistance value.

　　3) If the voltage pole point P is located inside the curve, the measured grounding resistance value is greater than the actual grounding resistance value.

Figure 1 Movement trajectory of voltage pole P compensation point