As a core component of the power distribution network, the design and implementation of the grounding system for distribution transformers are directly critical to the safe and stable operation of the grid, as well as the protection of personnel and equipment. To ensure the reliable operation of transformers, a complete and code-compliant grounding installation must be established. This article provides a systematic explanation of the technical requirements, functional principles, and engineering practices for grounding points.

I. Core Functions and Configuration Principles of Grounding Points

Generally, a distribution transformer requires at least two independent grounding electrodes with their respective down conductors:

1.  Transformer Tank (Protective) Grounding

       Primary Purpose: To provide a low-impedance path for the discharge of fault currents and lightning currents, preventing the tank from becoming energized due to insulation failure or lightning surge overvoltage, thereby ensuring the safety of operating personnel.

       Technical Requirements: The grounding resistance must comply with national or industry standards (e.g., DL/T 621), typically requiring a value not exceeding 4Ω. In areas with high soil resistivity, resistance reduction measures (such as using resistance-reducing agents, deep-well grounding, or extended grounding grids) are necessary.

       Implementation: The transformer tank is reliably connected to pre-buried grounding electrodes (e.g., angle steel, steel pipes, or copper-clad steel rods) via galvanized flat steel or copper cables. All connection points must utilize exothermic welding or dedicated clamps to ensure a permanent, low-resistance, and corrosion-resistant electrical connection.

2.  Neutral Point (System) Grounding

       Primary Purpose: To stabilize the system potential relative to earth, providing a path for unbalanced currents; facilitating the rapid detection and clearance of single-phase ground faults in coordination with relay protection devices; and limiting system overvoltage levels (e.g., arcing ground overvoltage).

       Technical Requirements: The neutral point grounding method (solid grounding, resistance grounding, Petersen coil/arc suppression coil grounding, etc.) depends on the design of the power supply system. The grounding resistance value must be determined based on system short-circuit current calculations to ensure the proper operation of protective devices.

       Implementation: A dedicated ground conductor is run from the neutral point to an independent grounding electrode. This grounding system should, where possible, be connected to the protective grounding grid at a single point to eliminate potential differences.

II. Special Conditions Requiring Additional Grounding Points

Beyond the two basic grounding points mentioned above, the following complex conditions necessitate consideration for adding or reinforcing grounding measures:

   Areas with High Soil Resistivity: When the measured grounding resistance cannot meet requirements, it is necessary to add grounding electrodes to form a composite grounding grid or install ring-type grounding and voltage grading conductors to improve grounding performance.

   Presence of Strong Electromagnetic Interference or Sensitive Electronic Equipment: To prevent ground-line noise coupling, a dedicated signal ground for secondary control circuits or monitoring equipment may sometimes be required, maintaining appropriate isolation from the main grounding grid.

   Flammable, Explosive, or High-Risk Environments: In areas such as chemical plants or gas stations, the grounding system must also consider explosion-proof requirements and static electricity dissipation paths, potentially requiring a denser grounding mesh.

   Large or Critically Important Transformers: To ensure redundant safety, the tank may require dual ground down conductors, connected to separate grounding electrodes to prevent failure from a single ground path break.

III. Full Lifecycle Management of the Grounding System

A professional grounding project encompasses not only installation but the entire process of design, construction, testing, and maintenance:

1.  Design Phase: Site soil resistivity measurements are required. Simulation calculations and design are performed based on geological conditions, system parameters, and safety standards.

2.  Construction and Acceptance: Construction must strictly follow drawings, and final measurement must be conducted using a ground resistance tester, with complete records retained. All welded joints should receive anti-corrosion treatment.

3.  Regular Maintenance and Inspection: Grounding installations can degrade due to corrosion, soil changes, or external damage. It is recommended to perform re-testing of grounding resistance and inspection of connection points every 1-3 years, especially before the thunderstorm season.

IV. Summary and Recommendations

In summary, the grounding of a distribution transformer is far more than a simple "two-point ground"; it is a comprehensive technical solution based on system safety, equipment protection, and environmental conditions. The minimum configuration consists of two independent grounds for the tank and neutral point, but actual engineering must involve refined design and validation tailored to the specific site context.

Best Practice Recommendations:

- Strictly Adhere to Codes and Standards: Base all work fundamentally on national standards, industry regulations, and equipment manufacturer requirements.

- Emphasize Geological Surveys: Accurate soil resistivity data is essential prior to grounding design.

- Ensure Construction Quality: Use qualified materials and workmanship; critical connection points must be robust and reliable.

- Establish Inspection Records: Implement regular testing and condition assessments to achieve full lifecycle management of the grounding system.

A well-designed grounding system acts as the "invisible guardian" for the safe operation of electrical equipment, and its importance cannot be overstated. Through scientific design, standardized construction, and ongoing maintenance, the long-term stable operation of distribution transformers can be maximally ensured, enhancing the overall power supply reliability of the distribution network.