In all power generation, transport and distribution systems it is possible to install an electrode or electrodes in the soil in order to earth the equipment and equipment within it. This study is generally called grounding. In this way, a return path to the fault current is shown in the problems in the electrical energy system. Earthing can be done in various ways. However, it is essential that the grounding system should not be able to show high resistance. Otherwise, the voltage on the machinery and equipment running on electricity cannot go into the ground and this puts people in danger for the safety of people and property. Nothing on earth is more abundant than earth. Sometimes the soil is the foundation of a building, and sometimes it is the food that gives people food. The area that concerns the engineers is the electrical (conductivity and resistance) aspect.
The grounding resistance (earth resistance) is the reaction of the earth during the electric current. Soil is actually a weaker conductor than conductors such as copper. However, if the field is large enough for the current, the resistance is low and the soil may become a good conductor. Therefore, there is a resistance between the conductors in the system and the soil. Before the installation of the facility, these measurements are made and the installation is performed after the necessary calculations and preparation. Earth resistance (specific resistance) 1 m³ is the resistance of the soil. The value depends on the structure of the soil and the rate of water in it. The resistance of a electrode to ground depends on the resistivity of the soil. The table contains a few examples. Insulation of each conductor against ground is measured by insulation tester (insulation megeri) while earth resistance tester (earth megeri) and conductors are isolated against each other. In short, all insulation resistance measuring devices (megers) are specially manufactured portable ohm meters.
For this reason, in order to avoid possible problems in the electrical system or to minimize the potential losses, the grounding resistances of the existing power stations, transformer stations or transformers in the system should be measured at regular intervals within a program. As a result of these measurements, the grounding resistance levels above the limit values must be reduced to normal values. The accepted limit grounding resistances for various electrical devices are as follows: 1 Ohm in large power stations and transformer stations 10 Ohm.
Factors Affecting Soil Resistance
Megger device is widely used in grounding resistance measurements. This device is based on AC voltage drop when operatingr. With the Megger device, an alternating voltage different from the mains voltage frequency is sent to the ground. The same frequency voltage taken from the soil is monitored and measured. During the measurement of the earth resistance, the ground is made in the ground. There are three electrodes in the classic earth meers: earth electrode (E), current electrode (C) and potential electrode (P). However, two piled measurements are more widely used.
Within the framework of electrical safety inspections, our company carries out the measurements of soil resistance in accordance with relevant legal regulations, standards and test methods published by domestic and foreign organizations. The following standard is taken into account in these studies:
- TSE K 187 Neutral earthing resistors
In the meantime, TSE continues to work on the following two standards:
- TST 2017114895 Neutral grounding resistors
- TST 2016114274 Measurement methods and evaluation of resistivity and earth propagation resistance in electrical systems (Electrical) (studies on this standard are in progress)
