The Total Noise: EN 50121-2 System Emission Standards

Introduction to EN 50121-2

A railway line is a massive, moving electromagnetic generator. The combination of high-voltage overhead lines, the pantograph drawing varying currents, and the sparks from wheel-rail contact creates a complex field of interference. EN 50121-2, titled “Railway applications – Electromagnetic compatibility – Part 2: Emission of the whole railway system to the outside world,” is the environmental guardian of the standard series.

Unlike other parts of the series that test individual components in a lab, EN 50121-2 looks at the “Big Picture.” It sets the limits for the maximum electromagnetic noise a railway line is allowed to emit into the surrounding environment, ensuring that a passing train doesn’t disrupt the TV signals of nearby houses or the sensitive equipment of a hospital located next to the tracks.

Snippet Definition: What is EN 50121-2?

EN 50121-2 is a European standard that specifies the limits for electromagnetic emissions (radiated fields) from the whole railway system—including the rolling stock, the infrastructure, and the power supply—into the external environment. It defines the measurement methods (e.g., antenna placement at 10 meters from the track) and permissible levels for both magnetic fields (low frequency) and electric fields (radio frequency).

The “Whole System” Approach

EMC is usually tested on a device in a shielded room. EN 50121-2 is unique because it tests the real world. It recognizes that interference isn’t just caused by the train; it’s the interaction between the Train (source) and the Infrastructure (antenna).

• Traction Power: The return current flowing through the rails creates a magnetic field loop.
• Pantograph Arcing: As the pantograph bounces on the wire, it creates high-frequency radio noise (broadband interference).
• Substations: Switching operations in traction substations contribute to voltage transients.

Measurement Protocol

The standard mandates strict geometry for validation tests to ensure repeatability.

• Antenna Distance: Measurements are typically taken at 10 meters from the center of the track. This represents the boundary where “public” space begins.
• Antenna Height: Specific heights are defined for measuring H-fields (loop antenna) and E-fields (biconical/log-periodic antennas).
• Traffic Conditions: Measurements are often taken during the passage of trains at maximum speed and during maximum acceleration/braking (when current draw is highest).

Comparison: EN 50121-2 vs. EN 50121-3

Understanding the hierarchy is crucial for compliance.

Frequency Ranges and Limits

EN 50121-2 divides the spectrum into two main battles:

1. Low Frequency (9 kHz – 150 kHz)

Dominated by the Magnetic Field (H-field) generated by the massive currents (thousands of Amperes) powering the train. Limits are set to prevent interference with sensitive legacy equipment or inductive loops.

2. High Frequency (150 kHz – 1 GHz)

Dominated by the Electric Field (E-field). The primary culprit here is the “sparking” (arcing) between the catenary and pantograph. If the contact quality is poor, the railway becomes a giant radio jammer. EN 50121-2 sets limits (in dBµV/m) to protect AM/FM radio, emergency services, and cellular networks.