The incoming cable specification for a 25000KVA transformer — answer only the cable specification.
Based on the 25000 kVA transformer capacity you provided, combined with Article 3.0.1 of GB 50052-2009 "Code for Design of Power Supply and Distribution Systems" (the supply voltage shall be determined according to the power consumption capacity) and the ampacity selection principles of GB 50217-2018 "Standard for Design of Cables of Electric Engineering," this capacity has far exceeded the economically applicable range of 10 kV supply. Typically, a supply voltage of 35 kV or higher is required. The cable specifications corresponding to two common schemes are provided below:
Scheme 1: 35 kV Supply (Recommended Scheme)
- Cable Type: YJV-26/35kV single-core or three-core XLPE-insulated power cable.
- Recommended Specification: YJV-26/35 1×630mm² (multiple single-core cables in parallel, commonly 2–3 per phase) or YJV-26/35 3×400mm² (three-core cable; multiple cables in parallel are required when the ampacity of a single cable is insufficient).
- Basis: At 35 kV, the rated current is approximately 412 A (I=S/√3U=25000/1.732/35≈412 A). Considering a reserved margin (at 80% load factor), the ampacity shall be ≥515 A. The ampacity of a single 1×630mm² copper-core cable laid in air is approximately 900–1000 A (25℃), which meets the requirement; the ampacity of a three-core 3×400mm² cable is approximately 600–700 A, which can meet the requirement with a single cable.
- Cable Type: YJV-8.7/15kV single-core or three-core cable.
- Recommended Specification: YJV-8.7/15 1×630mm² (multiple single-core cables in parallel, requiring 4–5 per phase) or YJV-8.7/15 3×400mm² (three-core cable requiring 3–4 in parallel).
- Basis: At 10 kV, the rated current is approximately 1443 A (I=25000/1.732/10≈1443 A). The ampacity of a single 1×630mm² cable is approximately 900–1000 A, so 2 per phase (total ampacity approximately 1800–2000 A) would be required; however, for multiple cables in parallel, correction factors shall be considered (Article 3.7.5 of GB 50217-2018), and the actual ampacity will decrease. It is recommended to use 4–5 per phase to ensure safety.
1. Voltage Level Priority: For a 25000 kVA transformer, a 35 kV incoming line should be the first choice; the 10 kV scheme requires approval by the local power supply department (usually the upper limit of single-circuit 10 kV supply capacity is approximately 10000–12000 kVA, Article 3.2.2 of GB 50053-2013).
2. Number of Cables and Laying Method: The final specification shall be comprehensively calculated in combination with the cable laying method (cable tray, conduit bank, direct burial), ambient temperature, and correction factors for multiple cables in parallel (Articles 3.7.3–3.7.5 of GB 50217-2018). It is recommended to commission a professional design institute to issue a cable cross-section calculation report.
3. Protection and Grounding: 35 kV cables shall be provided with grounding conductors (cross-section ≥25mm² copper core) and shall meet the grounding requirements for metallic shields in Article 3.8.1 of GB 50217-2018.
Please refer to the formal construction drawings of the design institute; the above are recommended specifications based on the codes.