1. Basic Standards

Product model: KS11-M-1250/10(6), or as specified by the customer. (Example: K—mining use; S—three-phase; 11—performance level; M—general mining type; 1250—rated capacity in kVA; 10(6)—high-voltage side voltage rating in kV.)

Standards: Design, manufacturing, testing, and acceptance shall fully comply with the IEC 60076 series of standards. In addition, they shall also comply with the relevant national standards of the target country (e.g., AS, BS, GOST, etc.; such requirements must be clearly specified).

Rated capacity: 1250 kVA.

Number of phases and frequency: Three-phase, 50 Hz or 60 Hz (must be specified in accordance with the grid requirements of the target country).

2. Rated Voltage and Voltage Regulation

High-voltage side (HV): 10 kV or 6 kV, 6.6 kV, 11 kV, etc. Must be compatible with the primary voltage of the project site’s power grid.

Tap range: ±2 × 2.5% or ±5%, with no-excitation manual voltage regulation (or on-load tap changing as required).

Low-voltage side (LV): 0.4 kV (400 V) or 0.69 kV (690 V). For a 1250 kVA transformer, a 690 V output is strongly recommended, as it can significantly reduce the low-voltage-side current, thereby lowering cable investment and losses.

Connection group designation: Dyn11. This connection configuration provides a stable neutral point and suppresses third-harmonic currents, making it the preferred choice for international mining projects.

3. Performance Parameters

Impedance voltage (Uk%): 6% (standard value; may also be specified as 5.5% or 6.5%, subject to calculation in conjunction with the system short-circuit capacity).

Cooling method: ONAN (oil-immersed self-cooling).

Insulation level:

High-voltage winding: Lightning impulse withstand voltage (LI) 75 kV, power-frequency withstand voltage (AC) 35 kV (for a 10 kV system).

Low-voltage winding: lightning impulse withstand voltage (LI) 5 kV, power-frequency withstand voltage (AC) 3 kV.

4. Losses and Energy Efficiency

No-load loss (Po): not more than 1,350 W. This is a key economic performance indicator; the supplier shall clearly specify the silicon steel sheet grade (e.g., 27ZH100 or higher).

Load loss (Pk at 75°C): not greater than 12,000 W. Full copper windings are explicitly required.

No-load current (Io): not greater than 0.8%.

Energy efficiency class: shall comply with IEC 60076-20 or the EU CoC Tier 2 standard and above (where applicable).

5. Structural Requirements

Core: Made from high-quality, high-permeability, low-loss cold-rolled grain-oriented silicon steel sheets, with a stepped lamination structure and a skewed-joint lap joint process.

Windings: The high-voltage winding is either layer-type or continuous-type, while the low-voltage winding is either helical-type or foil-type. The conductor material is 100% electrolytic copper.

Insulating Oil: High-quality mineral insulating oil compliant with IEC 60296. For environmentally friendly projects, natural ester (vegetable) insulating oil may be specified.

Oil tank and conservator: corrugated or flat-type oil tank with a detachable oil reservoir. The conservator is equipped with a glass oil level gauge, a desiccant breather (silica gel), and an oil filling valve.

Protection rating: Enclosure IP54 (dustproof and splash-proof) or higher. The coating system consists of an epoxy zinc-rich primer, an epoxy micaceous iron oxide intermediate coat, and a polyurethane topcoat, meeting the C4-M marine/industrial corrosion environment requirements.

Protection and Monitoring:

Gas relay: equipped with light-gas (alarm) and heavy-gas (trip) contacts.

Pressure relief valve: operating signal contact.

Thermometers: Oil Surface Temperature Indicator (OTI) and Winding Temperature Indicator (WTI), both equipped with PT100 resistance sensors, 4–20 mA analog output, and two pairs of independent alarm/trip contacts.

Terminals: High-voltage terminals shall be equipped with porcelain bushings or composite insulating bushings. Low-voltage terminals shall be copper busbar terminals, with clearly specified dimensions (e.g., 4 × 100 mm or determined by current rating).