What are the grounding requirements for 10 kV substations (or distribution stations)?

According to the relevant provisions of the "Code for Construction and Acceptance of Grounding Devices in Electrical Installations" (GB 50169), the grounding devices of 10kV substations (distribution stations) should meet the following main requirements:

◦ General Principle: Working grounding, protective grounding, lightning protection grounding, etc., should share a single grounding device, and its grounding resistance value should meet the minimum requirement among them.

◦ Conventional Requirements: The grounding resistance of an effective grounding system (usually used for 110kV and above) is generally required to be R ≤ 0.5Ω. For 10kV systems that are ungrounded, grounded via an arc suppression coil, or grounded via high resistance, the grounding resistance value of the substation must meet the following formula, and should generally not exceed 4Ω:

▪ R ≤ 120 / I (Formula 1)

◦ Equalization and Step Voltage: The grounding grid edge should be closed, and an equalization strip should be laid inside to reduce step voltage and contact voltage. High-resistivity pavement or buried equalization strips can be used at entrances and exits.

◦ All non-energized metal parts of electrical equipment, including metal casings, metal frames, cable armor, switchgear frames, transformer neutral points and casings, metal enclosures of distribution equipment, and cable trays/protective pipes, must be reliably grounded.

◦ Each piece of electrical equipment should be connected to the grounding trunk line or grounding grid with a separate grounding wire. Connecting multiple devices in series on a single grounding wire is prohibited.

◦ Independent lightning rods should have independent centralized grounding devices, and their grounding resistance should not exceed 10Ω.

◦ The underground connection point of the independent grounding device to the main grounding grid, from the transformer neutral point or the underground connection point of the main grounding grid for 35kV and below equipment grounding wires, should be no less than 15m along the length of the grounding conductor to prevent lightning backflashover.

◦ Metal pipes, cable sheaths, and metal pipelines entering and exiting buildings within buildings should be connected to the main equipotential bonding terminal block or grounding grid near the entrance to achieve equipotential bonding.

In summary, the core of grounding in a 10kV substation is to construct a low-resistance, continuous, reliable, and well-equalized integrated grounding network, ensuring effective connection of all grounded components to guarantee personal safety, reliable equipment operation, and effective lightning protection. Specific design and construction must strictly adhere to approved construction drawings and relevant national standards.

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 Shaanxi West Power Tongzhong Electrical Co., Ltd.
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