Electrical power supply in tunnels

Tunnels—whether road, rail, or waterway—constitute a constrained underground environment, often without direct access to an energy grid. Nevertheless, they must accommodate installations that require electrical power: standard and emergency lighting, ventilation, signalling, detection and communication systems, power outlets, pumping systems, and more.

• Very long distances – Several kilometres in the case of some tunnels. When using conventional 400 V low voltage, voltage drop and Joule losses become unacceptable beyond 500–800 m, or require oversized cable cross-sections.
• Harsh environment – Permanent humidity, water splashes, potentially corrosive atmosphere, dust, vibrations.
• Installation and operational constraints – Limited space, difficult access, requirement for 24/7/365 availability, infrequent and rapid maintenance, often carried out at night.

1. At the tunnel entrance, a substation steps up the voltage.
2. Power is distributed over several kilometres using very small cable cross-sections with negligible losses.
3. Every 1 to 2 km, watertight step-down transformers reduce the voltage to 230 V or 400 V, exactly where the energy is consumed.

1. Currents divided by 10 → Cable cross-sections are significantly reduced and costs kept under control.
2. Flexible, localised distribution — Fine adaptation to the tunnel layout, its length, the type of equipment, and its distribution.
3. Transformers are 100% watertight (IP68), dry-type or filled with vegetable oil.
4. Enhanced corrosion protection, resistance to shocks and vibrations.
5. Reduced maintenance, service life exceeding 30 years.

1. Permanent and emergency lighting
2. Ventilation and smoke extraction
3. Pumping systems
4. Variable message signs (VMS), signalling, video surveillance
5. Fire detection, radio communication, and supervision systems
6. Power outlets for worksites and technical rooms

1. Braus Tunnel: Power supply for communication relays distributed over 6 km.
2. Inelfe Tunnel: Tunnel lighting over more than 8 km during the construction phase.
3. Fréjus Tunnel: Lighting and safety systems over 12 km during the construction phase.

Contact our tunnel power supply experts. We carry out a free, customised study and provide you with the most reliable and cost-effective solution, regardless of the type or length of your tunnel.

Request a study → contact@augier.com