Laz Tunnel – Modern Infrastructure for Reliable Power Supply

The backup power supply project for the “Laz” tunnel on the E-763 highway (Preljina–Požega section) and the accompanying transformer stations TS1, TS2, TS3, and TS4 represent key elements of modern infrastructure that ensure stable and reliable power supply under all conditions, including interruptions in the main grid supply.

Tunel Laz Srbija

Overview of Transformer Stations (TS1, TS2, TS3, and TS4)

These four transformer stations have been designed and constructed to achieve maximum security, fault tolerance, and energy efficiency. Their primary role is to support the operation of the “Laz” tunnel by providing reliable power to all critical consumers, including ventilation systems, hydrotechnical installations, and UPS devices.

TS1 and TS4 are outdoor transformer stations, while TS2 and TS3 are indoor transformer stations located within the vehicle passageway.

The primary power supply comes from the 35/10 kV substation “Pakovraće,” while the backup power supply comes from the 35/10 kV substation “Krstac.” In addition to the two network power supply routes, backup power is also planned for all priority consumers via UPS devices and a Diesel Electric Generator (DEA) in the event of a power outage from both network supply routes. The backup power supply from the DEA is designed to supply all four transformer stations on the 10 kV side through a step-up transformer of 10/0.4 kV and ensure power to all priority consumers in the tunnel.

TS1: Reliability and Automation

  • SF6 medium-voltage switchgear with Easergy P3U30 digital protective relays.

  • Modular rectifier systems (110 VDC) and Zigbee sensors for monitoring temperature and humidity.

  • Automatic control via PLC controllers supporting IEC 61850 protocols.

TS2: Flexibility and Safety Innovations

  • Modular low-voltage switchgear of the Prisma Spacial SFP type.

  • Integrated arc detection sensors and real-time environmental monitoring.

  • Hermetically sealed SF6 circuit breakers with triple protection and voltage presence indicators.

TS3: Environmental Solutions and Digital Control

  • Hermetically sealed SF6 systems designed to minimize environmental impact.

  • Advanced PLC controllers and digital relays for precise control and monitoring.

  • Robust design for operation under demanding weather conditions.

TS4: Energy Efficiency and Innovation

  • Automated control and fault detection systems.

  • Advanced Zigbee sensors for monitoring key parameters such as temperature, humidity, and electrical arcs.

  • Modular rectifiers and high-capacity busbars.

Key Elements of the Backup Power Supply for the “Laz” Tunnel

Design of Electrical Installations

  • Installation of an oil transformer with a capacity of 3150 kVA and ONAN cooling, equipped with a Buchholz relay for internal fault protection

  • Implementation of an oil collection pit for environmentally safe oil containment in case of leaks.

  • Cable connections executed with medium-voltage cables (3x XHE 49-A 1×150/25 mm²).

Backup Power Supply via Diesel Electric Generator (DEG)

  • Diesel electric generator with a capacity of 2750 kVA, G3 performance class according to ISO 8528, with the following features:

    • Electronically regulated diesel engine with redundant startup.
    • Class H alternator with automatic voltage regulation (+/- 1%).
    • A daily fuel tank with a capacity of 2000 liters, providing autonomy of 4.3 hours at 82% load.
    • 4000 A protective switch with thermal-magnetic protection.

Protection and Automation System

  • Overvoltage protection integrated in accordance with technical standards.

  • Easergy P3 devices connected to the SCADA system, enabling precise monitoring and remote control.

  • A centralized control system synchronizes all backup power elements.

Ventilation and Thermal Control

  • DEG rooms equipped with motorized fans for heat dissipation, with additional fans activated by thermostats.

  • Ventilation ducts designed to minimize vibrations and noise.

Operational Scenarios During Power Outages

  • Automatic switching to the DEG in the event of a power outage, with detailed scenarios for returning to grid power.

  • Priority power supply for ventilation systems, pedestrian and vehicle passage ventilation, basic lighting, signaling, and emergency lighting.

Transformer stations TS1, TS2, TS3, and TS4, together with the implemented backup power supply, represent a synthesis of engineering precision and technological innovation. This project ensures the reliable operation of the “Laz” tunnel while meeting the highest standards of safety and sustainability.

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