Power Quality Optimization Solution for Subway Station Low-Voltage Distribution System

The low-voltage power distribution system (0.4 kV) of subway stations is responsible for supplying power to a wide range of critical loads. These include environmental control systems such as air conditioners and ventilation fans, disaster prevention and alarm systems, communication and signal equipment, as well as escalators and other passenger service facilities. The reliability and stability of the power supply are therefore essential for ensuring safe and efficient subway operation.

With the widespread adoption of variable frequency drive (VFD) technology in subway environmental control systems, especially in inverter chillers and ventilation equipment, Power Quality challenges have gradually emerged during trial operation. These issues not only affect the efficiency of electrical equipment but also pose potential risks to the stable operation of sensitive systems.

During on-site testing and system evaluation, several major Power Quality Problems were identified:

• Harmonic Pollution
  A large number of inverter-driven chillers and ventilation fans operate continuously within the station. These nonlinear loads generate significant harmonic currents, particularly the 5th, 7th, and 11th harmonics. Excessive harmonics lead to overheating of distribution cables, increased system losses, and potential electromagnetic interference to the station’s precision microelectronic signal systems and communication equipment.
• Reactive Power Fluctuations
  The load demand of escalators, air conditioning units, and other station facilities fluctuates greatly with passenger flow and operating conditions. Traditional capacitor-based compensation systems respond slowly to these dynamic changes and may even cause harmonic amplification under certain conditions. As a result, the power factor cannot be maintained at the required standard level, reducing the overall efficiency of the power distribution system.
• Limited Installation Space
  Subway stations are located underground, where installation space for electrical equipment is extremely limited. Power quality treatment equipment must therefore meet strict requirements in terms of compact design, high efficiency, and effective heat dissipation, while still delivering reliable performance in a confined environment.

Field measurements showed that the total harmonic current distortion (THDi) of the system reached 16.4%, with the 5th and 7th harmonics being the dominant components. The overall power factor was approximately 0.85, indicating insufficient reactive power compensation and significant harmonic interference.

To address these challenges, IntonePower provided an advanced power quality solution tailored to the subway station’s operating conditions. After the implementation of the solution, the system performance improved significantly. The current distortion rate was reduced from 16.4% to 1.9%, effectively eliminating harmonic interference within the distribution network. At the same time, the power factor increased to 1.00, achieving precise and dynamic reactive power compensation.

The solution demonstrated excellent compensation performance and successfully resolved both harmonic distortion and reactive power issues on site. As a result, the stability, efficiency, and safety of the subway station’s low-voltage power distribution system were significantly enhanced, ensuring reliable operation of critical subway infrastructure.