The S11 series 10kV/6kV to 400V dual high voltage oil immersed transformer is designed for applications that require reliable operation under two different primary voltage levels (10kV or 6kV) while maintaining a constant secondary output of 400V. Its unique winding structure allows seamless voltage switching and fine‑tuning without changing the turns per volt or output voltage.

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1. Key Design Features

1.1 Series‑Parallel Sections for Voltage Conversion

The transformer contains an even number of series‑parallel sections and several tap sections. All series‑parallel sections have identical dimensions. Their taps are led to a series‑parallel switch via cables. By operating this switch, you can connect the sections in series or parallel – enabling the transformer to switch between 10kV and 6kV primary voltage.

1.2 Tap Sections for Voltage Fine‑Tuning

The tap sections are connected to a tap changer. By cutting off or adding some tap sections, the number of effective turns increases or decreases. Therefore, you can achieve precise voltage fine‑tuning.

1.3 Constant Turns Per Volt & Output Voltage

When the transformer operates under either high‑voltage input (10kV or 6kV), the combination of series‑parallel switching and tap adjustment ensures:

• The turns per volt remains constant.
• The output voltage stays at the required 400V.

This design eliminates the need for a separate transformer for each primary voltage – saving cost and space.

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2. Technical Advantages

Feature	Benefit
Dual high‑voltage capability (10kV & 6kV)	One transformer covers two grid voltages
Series‑parallel switching	Simple, robust voltage conversion
Tap sections for fine‑tuning	Precise output voltage regulation
Constant turns per volt	Stable performance under both inputs
Oil‑immersed construction	Superior cooling, insulation, and overload capacity

✅ Ideal for regions where grid voltage may vary between 10kV and 6kV, or for applications that need to operate from two different supply voltages.

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3. Typical Applications

• Industrial plants with dual voltage supply
• Utility distribution networks (upgrading from 6kV to 10kV)
• Renewable energy collection (wind/solar) with flexible grid connection
• Mining and remote sites where voltage levels fluctuate

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4. Why Choose the S11 Series?

• Efficiency: S11 series meets low‑loss standards (lower than S9/S10).
• Reliability: Oil‑immersed design ensures long life in harsh environments.
• Flexibility: One transformer handles two primary voltages.
• Easy maintenance: Conventional oil‑immersed construction with simple tap changing mechanism.