What Is Ground Resistance?
The grounding resistance is the resistance encountered when the current flows from the grounding device to the ground and then flows to another grounding body or diffuses to a distance. The ground resistance value reflects the good degree of contact between the electrical device and the "ground" and the size of the ground network.
Ground resistance
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- Ground
- Many household appliances, especially large appliances such as refrigerators, washing machines, air conditioners, etc. use three-core power cords. In fact, as long as there are two neutral wires and live wires, the appliances that use ordinary commercial power can work normally. The extra wire is the ground wire, which means that these appliances must be grounded.
- The introduction of grounding technology was originally a protective measure to prevent electrical or electronic equipment from being struck by lightning. The purpose was to pass the lightning current generated by lightning.
- There are many factors affecting the ground resistance: the size (length, thickness), shape, number, burial depth, surrounding geographical environment (such as flat land, ditch, and sloping field are different) of the ground electrode, soil humidity, texture, and so on. In order to ensure the good grounding of the equipment, it is necessary to use a meter to measure the grounding resistance.
- The measurement methods of ground resistance can be divided into: voltage and current meter method, ratio meter method and bridge method. According to the specific measuring instrument and the number of poles, it can be divided into: manual ground resistance meter method, clamp ground resistance meter method, voltage and current meter method, three-pole method and four-pole method.
- When measuring the ground resistance, some factors cause the ground resistance to be inaccurate:
- (1) The soil composition around the ground network is inconsistent, the geology is different, the density is different, and the degree of wetness and dryness is different. It has dispersibility, and the stray current on the ground surface, especially overhead ground wires, underground water pipes, cable sheaths, etc., has a special impact on the test Big. Solution: Take different points for measurement and take the average.
- (2) The direction of the test line is wrong, and the distance is not long enough. Solution: pinpoint the test direction and distance.
- (3) The resistance of the auxiliary ground electrode is too large. Solution: Sprinkle water on the ground pile or use a resistance reducing agent to reduce the grounding resistance of the current pole.
- (4) The contact resistance between the test clip and the ground measurement point is too large. Solution: Polish the contact points with a file or sandpaper, and fully clamp the polished contacts with a test lead clip.
- (5) Impact of interference. Solution: Adjust the pay-off direction, try to avoid the direction of great interference, and reduce the meter readings.
- (6) Instrument usage problems. Battery is low. Solution: Replace the battery.
- (7) The accuracy of the instrument decreases. Solution: Recalibrate to zero.
- The accuracy of the ground resistance test value is one of the important factors in determining whether the ground is good. Once the test value is inaccurate, it will either waste manpower and material resources (the measured value is too large), or it will bring hidden safety hazards to the grounding equipment (the measured value is too small). [2]
- (1) The measurement of grounding resistance is sometimes performed in the field. Therefore, the measuring instrument should be sturdy and reliable, with its own power supply, light weight, small size, and strong adaptability to harsh environments.
- (2) More than 20dB anti-interference ability, can prevent stray current or electromagnetic interference interference in the soil.
- (3) The meter should have an input impedance greater than 500kW in order to reduce the measurement error caused by the contact resistance between the auxiliary pole probe and the soil.
- (4) The frequency of the measurement signal in the instrument should be between 25Hz and 1kHz. The frequency of the measurement signal is too low and too high, which is likely to cause polarization effects, or the increase of the induction effect between the test lead wires, so that the inductance or capacitance between the leads , Resulting in a larger measurement error, that is, the pole error.
- (5) When the power consumption allows, the test current should be increased as much as possible. A larger test current is beneficial to improve the anti-interference performance of the instrument.
- (6) The meter should be simple to operate, and the reading should preferably be displayed digitally to reduce the reading error.