Understanding Traction Substation Transformers

Traction Substation Transformers

Traction substation transformers are critical components in railway electrification. They step down high-voltage power from the grid to a suitable voltage for railway traction systems. These transformers ensure stable and efficient power supply for electric trains.

1. Function & Purpose

Step down high-voltage AC power from transmission lines (e.g., 132 kV, 110 kV, 66 kV, 33 kV) to the required railway traction voltage (e.g., 25 kV AC, 750V DC, 1500V DC).
Provide electrical isolation between the power grid and the railway system.
Improve power quality and reliability for smooth train operations.

2. Types of Traction Substation Transformers

A. Single-Phase Traction Transformers (For AC Railways)

Used in AC electrified railways (typically 25 kV, 50 Hz or 60 Hz).
Step down from high-voltage three-phase grid to single-phase 25 kV for trains.
Often connected in a Scott-T or V/V configuration to balance the load on the three-phase grid.

B. Rectifier Transformers (For DC Railways)

Used in DC railway systems (like metros and trams running on 750V, 1500V, or 3000V DC).
Step down AC voltage and supply it to rectifiers, which convert it to DC.
Designed to handle harmonics and pulsed loads from rectifiers.

C. Autotransformers (For 2×25 kV Systems)

Used in high-speed and long-distance railways with 2×25 kV AC systems.
Reduce voltage drop over long distances and improve efficiency.
Connected in series with the overhead catenary to provide better power transmission.

3. Key Features & Design Considerations

✅ High Efficiency – Designed to minimize energy losses.
✅ Thermal Management – Equipped with efficient cooling (ONAN, ONAF, OFAF).
✅ Electromagnetic Compatibility (EMC) – Minimizes interference with signaling systems.
✅ Load Handling – Designed to withstand fluctuating and regenerative loads.

4. Applications in Different Railway Systems

🚆 High-Speed Railways – Use single-phase or autotransformer systems (25 kV AC, 2×25 kV AC).
🚋 Metro & Trams – Use rectifier transformers (750V, 1500V DC).
🚄 Conventional Railways – Typically use 25 kV AC traction transformers.