Ground resistance tester Victor 4108application

lPurpose of grounding
Grounding is an electrical safety measure taken to ensure the normal operation of electrical equipment and personal safety. Commonly used methods include protective grounding, working grounding, lightning protection grounding, shielding grounding, anti-static grounding, etc. A good grounding system can introduce potential leakage currents, static charges, and lightning currents that may occur on electrical and other production equipment into the ground, thereby avoiding personal electric shock and potential accidents such as fires and explosions.


lDefinition of Grounding Resistance
A good grounding system should have a sufficiently small grounding resistance. Ideally, the grounding resistance should be zero, but in reality, the grounding resistance is not zero. Figure 1 shows a simple grounding system, which consists of the grounded body (the grounded electrical equipment machine) and the grounding electrode in contact with the ground, as well as the grounding wire that connects them electrically.
The grounding resistance of this system includes the following three types of resistors:
① The conductor resistance of the grounding wire and grounding electrode itself
② Contact resistance between the surface of the grounding electrode and the soil in contact with it
③ The resistance of the soil around the grounding electrode
Among these three factors, ③ has a greater impact on grounding resistance, and the resistance of soil is the main part of grounding resistance, also known as earth resistance. Therefore, measuring soil resistance will be particularly important.
Figure 1




lPrinciple of Grounding Resistance Measurement
VICTOR 4108 uses the potential drop method to test ground resistance.

The current I generated by the AC source U flows through the measured grounding resistance RE and the auxiliary grounding electrode RH, and then returns to the current source U. In this way, the measured grounding resistance RE has a voltage Ue, which can be detected and measured by the probe S. Due to the high impedance of the voltage measurement circuit, the influence of the resistance RS of the voltage pole can be ignored. The current I is measured through an internal current measurement circuit. Therefore, the measured grounding resistance is RE=Ue/I.
In the actual testing process, due to the impact of power frequency on the measurement circuit, the measurement data is inaccurate. Therefore, the frequency of the AC source cannot be 50Hz/60Hz, and other frequency points should be selected to ensure the accuracy of the measurement data. VICTOR 4108 not only uses digital filtering algorithms for power frequency 50Hz/60Hz interference suppression, but also utilizes four different AC source frequencies of 94Hz, 105Hz, 111Hz, and 128Hz to greatly suppress power frequency interference. These four frequencies can be manually or automatically set. When using automatic setting, the instrument can automatically select the appropriate frequency based on the current interference noise, making the measured data more accurate and reliable.




lTesting of soil resistivity
Measuring soil resistivity can help us understand the local soil resistance and provide important design information when selecting sites for substations, communication stations, etc., so that the designed grounding resistance can meet the requirements of these occasions.
VICTOR 4108 tests soil resistivity using the method developed by Wenner (F. Wenner) and the 4-pole method. By simply setting the ground pile spacing parameter, VICTOR 4108 can automatically calculate the soil resistivity. Press the "MEMU" button to enter the system menu , select the "Length" setting item, and set the interval between 1-30m, such as 20m.
Perform connection testing according to the following diagram.


Press the "TESE" button, VICTOR 4108 will calculate according to the following formula,
ρ＝2paR
ρ: The average value of soil resistivity (W · m)
a: Distance between grounding rods (m)
R: Measure resistance (W)
The display screen shows the soil resistivity as the result, and also displays the current interference voltage, interference frequency, and other information to facilitate further analysis of the measured soil resistivity.
Tip: When the noise symbol "" is displayed on the screen, the measured soil resistivity will be inaccurate and needs to be retested until the noise symbol is no longer displayed. Only then will the measured soil resistivity be considered valid data.
lMeasurement of Grounding Resistance of High Voltage Iron Towers

When measuring the grounding resistance of a high-voltage iron tower, we need to measure the grounding resistance of the high-voltage iron tower, and sometimes we also need to measure the grounding resistance of each bracket grounding wire of the high-voltage iron tower. During testing, we usually need to disconnect the overhead grounding wire. Because there are overhead grounding wires on high-voltage towers, it connects all high-voltage towers together, which means that it connects the grounding resistance of all high-voltage towers in parallel. In order to measure the grounding resistance of a certain high-voltage tower, its overhead grounding wire must be disconnected before measurement can be carried out; If you want to measure the grounding resistance of a certain bracket of a high-voltage iron tower, you not only need to disconnect the overhead ground wire, but also disconnect the grounding wires on the high-voltage iron tower base one by one before measuring (there is more than one grounding wire on the high-voltage iron tower base). This measurement method is difficult to operate in practical situations and requires a lot of manpower and material resources to conduct testing. However, VICTOR4108 only needs to be paired with a clamp head to test the grounding resistance of high-voltage towers or a certain bracket grounding wire without disconnecting the overhead and grounding wires.
Test the connection according to the following diagram
As shown in the above figure, VICTOR 4108 adopts the electrode selection method, which first measures the grounding resistance value of each bracket grounding wire. Since the total resistance of the high-voltage tower is the parallel resistance of all support grounding wires, the total resistance R of the high-voltage tower can be calculated according to the following formula_total



Tip: When the noise symbol "" is displayed on the screen, the measured grounding resistance will be inaccurate and needs to be retested until the noise symbol is no longer displayed. The measured grounding resistance value is considered valid data.


lMeasurement of Grounding Resistance Without Rod

When measuring the grounding resistance of a single branch in a multi grounding system, VICTOR 4108's "rodless" testing method provides a perfect solution. It can measure the grounding resistance of a single branch without disconnecting other grounding systems or finding a suitable location for installing auxiliary electrodes.
Its working principle is as follows:



In a grounding system, the sum of the parallel grounding resistances of all branches is much smaller than the grounding resistance of a single branch. So there is the following formula:

If the parallel connection of R1... Rn resistors is much smaller than the measured ground resistance Rx:

then.
According to the above principle, VICTOR 4108 should be connected and tested according to the following diagram



VICTOR 4108 is equipped with two current clamps. One clamp inputs the induced voltage into the grounding system network, while the other clamp measures the current of the measured branch according to the formulaYou can calculate the grounding resistance of a certain branch.