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The traction transformer is a highly specialized core equipment designed exclusively for electrified railways (high-speed rail, bullet trains, standard rail) and urban transit systems (subway, light rail). Traction transformers deliver stable power conversion under complex line operating conditions, and its primary function is to step down high-voltage grid power (110kV/220kV) to the precise voltage required by electric locomotives (27.5kV/55kV). Beyond voltage conversion, the traction power transformer achieves critical electrical isolation, phase transformation, and dynamic three-phase grid load balancing. Built to endure extreme, frequent short-circuit impacts and massive short-term overloads, it is the beating heart of modern transportation infrastructure.
Core Parameters:
• Rated Capacity: 10MVA ~ 63MVA (Supports 1.5x~2.0x short-term massive overload).
• Voltage Configuration: Grid side 110kV/220kV stepped down to Traction side 27.5kV/55kV.
• Special Vector Groups: V/v, Scott, YNvd, YNd11 optimized for transit load balancing.
Product Features
Traction power transformer utilizes specialized connection groups (like Scott or V/v) to transform three-phase grid power into two-phase or single-phase traction power, drastically reducing negative sequence currents on the public grid. As core substation hardware, traction transformers are purpose-built to handle volatile railway power supply scenarios.
This traction power transformer is engineered for the violent load fluctuations of accelerating locomotives. Capable of safely enduring short-term overloads of 1.5 to 2.0 times its rated capacity without overheating, all traction transformers undergo rigorous overload endurance testing before delivery.
Traction networks face frequent pantograph arcing and short-circuits. The reinforced mechanical core and rigid winding structure of a standard traction power transformer effortlessly absorb brutal electromagnetic shockwaves, a key structural advantage shared by all heavy-duty traction transformers.
Adheres strictly to high-voltage standards (e.g., 110kV Class with LI250kV/AC95kV withstand levels), guaranteeing zero electrical breakdown under massive high-speed rail voltage surges.
Available with On-Load Tap Changers (OLTC) or Off-Circuit Tap Changers (OCTC), allowing substations to maintain precise contact-line voltages despite varying train distances and grid fluctuations.
Equipped with ONAN, ONAF, or high-tier OFAF cooling systems to rapidly extract intense heat generated during rush-hour traffic peaks, ensuring non-stop transit operations.
Key Specifications (Traction Transformer)
| Parameter | Typical Value | Description |
| Rated Capacity | 10MVA ~ 63MVA | Heavy-duty capacity engineered specifically for electrified railway substations. |
| Rated Voltage | HV: 110kV / 220kV LV: 27.5kV / 55kV | Steps down national transmission grids to dedicated overhead catenary line voltages. |
| Phase Configuration | 3-Phase Grid to 1-Phase/2-Phase | Solves the complex problem of feeding single-phase trains from a three-phase public grid. |
| Vector Group | V/v, Scott, YNvd, YNd11 | Specialized phase-shifting connections to maximize grid balance and isolate harmonics. |
| Short-Circuit Impedance | 8% ~ 12% | Purposefully elevated impedance to blunt the severe impact of frequent railway short-circuits. |
| Overload Capability | 1.5x ~ 2.0x Rated Capacity | Safely powers multiple trains accelerating simultaneously within the same power sector. |
| Insulation Level | LI250kV / AC95kV (110kV Class) | Massive dielectric strength to survive lightning strikes and switching overvoltages. |
Full Series Technical Reference (Traction Platform: 10MVA ~ 63MVA)
| Rated Capacity (MVA) | High Voltage (kV) | Low Voltage (Traction) (kV) | Impedance (%) | Cooling Method | Typical Application |
| 10 | 110 / 220 | 27.5 / 55 | 8.0 ~ 10.5 | ONAN / ONAF | Urban Light Rail / Subway Depots |
| 16 | 110 / 220 | 27.5 / 55 | 8.0 ~ 10.5 | ONAN / ONAF | Standard Electrified Railways |
| 20 | 110 / 220 | 27.5 / 55 | 8.5 ~ 10.5 | ONAF | Intercity Commuter Railways |
| 31.5 | 110 / 220 | 27.5 / 55 | 10.0 ~ 10.5 | ONAF | High-Speed Rail (HSR) Substations |
| 40 | 110 / 220 | 27.5 / 55 | 10.0 ~ 12.0 | ONAF / OFAF | HSR Main Hubs |
| 50 | 110 / 220 | 27.5 / 55 | 10.5 ~ 12.0 | ONAF / OFAF | Heavy Haul Freight Railways |
| 63 | 110 / 220 | 27.5 / 55 | 10.5 ~ 12.0 | OFAF | Ultra-Heavy Haul / Major Transit Hubs |
* The table above illustrates standard traction transformer capacities. Actual weights, dimensions, and precise impedance values are rigorously customized based on the specific railway's catenary design (e.g., AT power supply vs. direct power supply) and grid integration constraints.
FAQ
Traction transformers face a unique electrical physics problem: the national power grid provides Three-Phase AC power, but electric trains run on Single-Phase AC power via the overhead catenary wire. Pulling massive amounts of power from just one phase of a three-phase grid would cause severe "three-phase unbalance," destabilizing the local power grid and damaging other generators.
1) V/v Connection: This uses two single-phase transformers connected in a V-shape. It takes three-phase power from the grid and outputs two separate single-phase lines. One line feeds the trains going "North," and the other feeds the trains going "South." This partially balances the load across the three grid phases.
2) Scott Connection: This is a highly advanced mathematical winding configuration. It flawlessly converts a balanced three-phase input into two independent, 90-degree phase-shifted, single-phase outputs of equal voltage. If the train traffic in both directions is equal, the Scott transformer draws perfectly balanced power from the three-phase grid, entirely eliminating "negative sequence currents" and protecting grid stability.
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E-mail: junqiu.wang@czguanghui.cn
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