The 2x25 kV AT Feeder System: Why Indian Railways is Upgrading Its Traction Network
March 2026 · USTL Technical Team
Indian Railways has undertaken one of the world's most ambitious railway electrification programmes, with over 99% of its broad-gauge network now electrified using the 25 kV AC single-phase system. But electrification is only the beginning. The next phase of modernization involves upgrading the traction power supply system itself — transitioning from the conventional 1x25 kV system to the more efficient 2x25 kV Auto Transformer (AT) feeder system.
What is the 2x25 kV AT System?
In the conventional 1x25 kV system, power is fed to the overhead equipment (OHE) from traction substations typically spaced 40–60 km apart. The return current flows through the running rails and earth, which can cause interference with signaling systems and nearby communication lines.
The 2x25 kV AT system introduces an additional wire — the negative feeder — running parallel to the contact wire. Auto transformers installed at regular intervals (typically every 10–15 km) along the track balance the voltage between the contact wire and the negative feeder. This arrangement effectively doubles the feeding voltage to 50 kV while maintaining 25 kV at the pantograph, allowing for longer feeding distances and significantly reduced return current through the rails.
Why is Indian Railways Making This Transition?
Several factors are driving the shift. First, as train speeds increase and heavier freight loads demand more traction power, the conventional 1x25 kV system faces voltage regulation challenges over long distances. The 2x25 kV system can maintain adequate voltage levels over much longer feeding sections, reducing the number of traction substations required.
Second, the reduced rail return current in the AT system significantly decreases electromagnetic interference with signaling and communication systems — a critical requirement as Indian Railways deploys modern electronic interlocking and communication-based train control systems. Third, the AT system is inherently more energy-efficient due to lower transmission losses, which aligns with Indian Railways' commitment to reduce its carbon footprint and energy costs.
What Does the Upgradation Involve?
Upgrading an existing 1x25 kV section to a 2x25 kV AT system is a complex undertaking. It involves installation of auto transformers at regular intervals along the track, erection of additional OHE masts and structures to carry the negative feeder, modifications to the existing traction substations, and installation of sectioning and paralleling posts.
All of this must be executed while maintaining uninterrupted train operations — one of the most challenging aspects of the work. The construction methodology typically involves working in pre-planned traffic blocks of limited duration, requiring precise coordination between the construction team, railway operations, and signaling departments.
The Opportunity Ahead
The Ministry of Railways has identified several high-density corridors for AT system upgradation. For EPC companies with experience in railway electrification and OHE structure manufacturing, this represents a significant and growing opportunity. The technical complexity of these projects — requiring integration of civil, structural, electrical, and telecommunications disciplines — favours companies with broad engineering capabilities and a track record of working within the railway environment.
As India continues to modernize its railway infrastructure to support higher speeds, heavier loads, and cleaner operations, the 2x25 kV AT system will become the standard for all high-density routes.