The Voltage Rules: EN 50163 and Railway Supply Systems

What is EN 50163?

EN 50163 is the fundamental European Standard titled “Railway applications – Supply voltages of traction systems.” It specifies the main characteristics of the voltages measured at the pantograph (or contact shoe) of the rolling stock and at the substation busbars.

In a railway network, the voltage is never constant. It fluctuates due to line losses, the number of trains accelerating, and the energy fed back during regenerative braking. EN 50163 establishes the “rules of the road” for these fluctuations, defining the nominal voltages ($U_n$) and the permissible permanent and non-permanent variations. It ensures compatibility between the infrastructure (Fixed Installations) and the train (Rolling Stock).

Standard Nominal Voltages

The standard defines the specific voltage systems authorized for use in Europe. Any train or electrification project must adhere to one of these standardized values to ensure interoperability.

• DC Systems: 600 V, 750 V (Trams/Metros), 1500 V, 3000 V (Mainlines).
• AC Systems: 15 kV at 16.7 Hz (Central Europe), 25 kV at 50 Hz (High Speed/Standard).

Understanding Voltage Limits ($U_{min}$ to $U_{max}$)

EN 50163 introduces specific terminology to describe the operating range:

$U_n$ (Nominal Voltage): The ideal designated value (e.g., 25 kV).
$U_{min1}$ / $U_{max1}$: The lowest and highest voltages that can occur permanently (indefinitely). The train must perform normally within this range.
$U_{max2}$: The highest non-permanent voltage (short duration). This typically occurs during regenerative braking when a train pumps energy back into the line. The system can only tolerate this for a limited time before protection devices trip.

Comparison: Operating Ranges for Common Systems

The following table illustrates the permissible ranges for the most common traction systems defined in the standard.