What is a Neutral Section in a railway?

A Neutral Section is an insulated, dead section in the overhead power line that separates two different electrical phases. It prevents short circuits when the train's pantograph passes from one power source to another.

What happens if a train stops in a Neutral Section?

If a train stops directly in a Neutral Section, it cannot draw power to restart. In this scenario, another locomotive (diesel or battery-operated) is usually required to push or pull the stranded train out of the dead zone, or the train may use onboard emergency batteries if equipped for short movements.

How does a train pass through a Neutral Section?

The train uses momentum to coast through. The Automatic Power Control (APC) system opens the main circuit breaker before entering and closes it after exiting, ensuring no electricity is drawn during the transition.

The Power Gap: Understanding the Neutral Section (Phase Break) in Railways

What is a Neutral Section in railways? Discover how this critical “dead zone” separates electrical phases, prevents short circuits, and ensures safe OLE transitions.

December 9, 2025 7:09 pm

What is a Neutral Section?

A Neutral Section (also known as a Phase Break or Dead Zone) is a short, electrically isolated section of the Overhead Line Equipment (OLE) used in railway electrification. Its primary function is to separate two different electrical supplies—such as different phases from adjacent Traction Substations—preventing a bridge-over short circuit as the train’s pantograph passes through.

Why is a Neutral Section Necessary?

In AC electrification systems, power is supplied from the national grid through various substations. These substations often feed the catenary with different phases to balance the grid load. Without a Neutral Section:

The pantograph would momentarily touch two live wires with different phases simultaneously.
This would cause a massive phase-to-phase short circuit (flashover).
It could damage the catenary, the pantograph, and the substation equipment.

How It Works: The APC System

Trains cannot draw power while passing through this dead zone. The process is managed by the Automatic Power Control (APC) system:

Warning: Trackside magnets inform the train that a Neutral Section is approaching.
Cut-Off: The train’s Vacuum Circuit Breaker (VCB) automatically opens, cutting off power to the traction motors.
Coasting: The train coasts (drifts) through the insulated section via momentum.
Re-connection: Once clear of the section, the VCB closes, and power is restored.

Comparison: Phase Break vs. System Break

While they look similar, Neutral Sections serve different purposes depending on the electrical boundary.

Feature	Phase Break (Neutral Section)	System Break
Function	Separates two supplies of the same voltage but different phases (e.g., 25kV AC Phase A vs. Phase B).	Separates two different voltage systems (e.g., 25kV AC vs. 1.5kV DC).
Length	Usually short (Short Neutral Section) or medium length.	Often longer to ensure no accidental arcing between systems.
Operation	Requires VCB open/close (automatic via APC).	Requires pantograph lowering or system switch-over.

Key Components of a Neutral Section

Insulators: Ceramic or composite glass fibre (PTFE) rods inserted into the contact wire.
Track Magnets: Located on sleepers to trigger the APC receiver on the train.
Arc Traps: Devices designed to divert any residual electrical arcs away from the structure.