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　　What causes excessive grounding resistance of transformers

　　(1) The material of the grounding device is unqualified. Due to non-standard embedding of grounding bodies, unqualified installation process, loose connections between grounding bodies and grounding wires, and excessively dry soil, the grounding resistance may become too large.

　　(2) Due to insufficient understanding of the importance of the transformer grounding wire, the cross-section of the neutral line may be selected too small, or due to external damage, theft of the grounding wire, etc., it may lead to disconnection of the grounding wire or excessive grounding resistance.

　　Preventive measures to avoid excessive grounding resistance of transformers

　　(1) Strict construction techniques and standardize the embedding of grounding bodies. Grounding devices are generally made of steel pipes, angle steel, flat steel, and steel stranded wires. The embedding depth should not be less than 0.5~0.8m. The construction of the grounding device should generally be carried out simultaneously with the foundation construction, with specific requirements as follows.

　　① The depth of the grounding trench should meet the design requirements, generally 0.5~0.8m, and in arable land, it should be laid below the tillage depth. The width of the grounding trench is generally 0.3~0.4m, and all debris that may affect the contact between the grounding body and the soil should be removed from the trench.

　　② The specifications of the steel pipe and the depth of penetration into the soil should meet the design requirements. The grounding body should be driven vertically into the ground and fixed to avoid increasing the street resistance. In mountainous areas and areas with high soil resistivity, tubular grounding devices should be minimized, and surface-buried grounding devices should be adopted instead.

　　③ The grounding down-conductor should be laid along the pole and led down, as short and straight as possible to reduce its impulse reactance. The grounding down-conductor is fixed to the tower with supports, and the straight-line distance between supports is usually 1.0~1.5m, with 0.1m for turning parts. Electrician's Home

　　④ Except for the disconnection point reserved for measuring grounding resistance, the grounding down-conductor should not have any other joints. The connections of the grounding device should ensure contact and be welded. The connection between the grounding down-conductor and the reserved disconnection point for measuring grounding resistance should be bolted, and the connecting bolts should be galvanized for rust prevention.

　　⑤ After the grounding body is laid, backfill soil should be used, and debris such as stones that may affect the contact between the grounding body and the soil should not be buried.

　　(2) Select an appropriate position on the neutral line of the transformer and perform multiple-point repeated grounding of the neutral line. In this way, when the neutral line breaks at a certain point, due to multiple grounding, the neutral line current can still return to the transformer neutral point through the earth, the potential of the neutral line remains zero, and the voltage of each phase load remains the normal phase voltage.

　　(3) Install a residual current operated protective device after the user's electricity meter. When the user installs the protective device, if the grounding resistance at the transformer grounding point is too large, the earth potential will no longer be zero. At this time, a current will flow through the protective device and the earth to the transformer grounding point. This current will cause the protective device to operate and disconnect the grounding point, preventing the rise of the earth potential. In addition, after installing the protective device, when a person touches the phase wire, the protective device will also operate, thereby ensuring personal safety.