The Power Processors: EN 50207 Rolling Stock Converters

Introduction to EN 50207

The electricity collected from the overhead line (e.g., 25kV AC or 1500V DC) is useless to a modern AC traction motor or a passenger’s laptop charger in its raw form. It must be chopped, rectified, inverted, and smoothed. EN 50207, titled “Railway applications – Electronic power converters for rolling stock,” is the bible for the devices that perform this alchemy.

Whether it is the massive Traction Inverter that drives the wheels or the smaller Auxiliary Converter that powers the air conditioning and lights, EN 50207 sets the rules. It ensures that these high-power electronic boxes can withstand the vibration, moisture, and electrical surges of the railway environment while managing the immense heat generated by switching thousands of Amperes.

Snippet Definition: What is EN 50207?

EN 50207 is a European standard specifying the requirements for the design, manufacture, and testing of electronic power converters installed on board railway rolling stock. It covers traction converters, auxiliary converters, and battery chargers. It defines the mandatory testing regime (Type Tests vs. Routine Tests), rating classes, and cooling requirements to ensure reliability and safety. (Note: It is largely equivalent to IEC 61287).

Scope of Application

The standard applies to all power electronic assemblies on the train:

• Line Converters (Rectifiers): Converting AC catenary voltage to DC Link voltage.
• Motor Inverters: Converting DC Link voltage to Variable Voltage Variable Frequency (VVVF) AC to drive the motors.
• Auxiliary Converters (APU): Creating fixed 400V 50Hz AC for hotel loads (HVAC, sockets).
• Battery Chargers: Stepping down voltage to charge the 110V/24V batteries.

The Testing Regime

EN 50207 is famous for its rigorous testing tables. A converter cannot be installed on a train until it survives these trials.

1. Type Tests (Design Validation)

Performed on a single prototype to prove the design works.

• Temperature Rise Test (Heat Run): The most critical test. The converter runs at full load until temperatures stabilize. Sensors verify that the semiconductors (IGBTs) and capacitors do not exceed their thermal limits.
• Short Circuit Test: Simulating a catastrophic failure (e.g., motor short) to prove the protection systems react fast enough to prevent an explosion.

2. Routine Tests (Quality Control)

Performed on every single unit coming off the production line.

• Dielectric Test (Hi-Pot): Applying high voltage to check insulation integrity.
• Functional Test: Verifying the logic and basic operation.

Comparison: EN 50207 vs. EN 50155

These two standards often appear together in specifications.

Technical Challenges Addressed

Cooling Methods: EN 50207 requires clear definition of the cooling medium.

• Natural Convection: Used for small chargers.
• Forced Air: Fans blowing over heatsinks (noisy, prone to dust clogging).
• Liquid Cooling: Water/Glycol pumped through cold plates (efficient, compact, but risk of leaks).

Semiconductor Protection: The standard mandates checks on the “Safe Operating Area” (SOA) of the switching devices (GTOs, IGBTs, or SiC MOSFETs) to ensure they aren’t stressed beyond their limits during switching transients.