The AT feeding system represents a sophisticated approach to railway electrification, leveraging advanced transformer technology and optimal electrical configurations to enhance power delivery efficiency and system reliability. Its design considerations cater to the specific needs of modern railway operations, ensuring seamless integration with signalling, communication, and control systems for safe and efficient train operations.

Components of AT Feeding System

1. Auto Transformer: The core component of the AT feeding system is the auto transformer. Unlike conventional transformers with separate primary and secondary windings, an auto transformer has a single winding with taps at various points. This allows for voltage regulation and step-up/down functions efficiently.
2. Neutral Point Connection: In the AT feeding system, the neutral point of the transformer is connected to the railway track (rail). This connection serves as the return path for the rail current back to the power feeding system. By utilizing the rail as part of the electrical circuit, the AT system reduces impedance issues and improves overall efficiency.
3. Feeding Line: The feeding line carries the AC voltage (typically 25 kV for conventional railways and 2x25 kV for high-speed railways) from the substations to the railway overhead catenary system. It is designed to handle the power demand of trains while ensuring stable voltage supply.
4. Substation Equipment: Each substation along the railway route houses the AT feeding system equipment. This includes transformers, switchgear, protection devices, and control systems. The equipment ensures proper voltage regulation, fault protection, and operational control of the feeding system.
5. Cooling Systems (if applicable): Larger capacity AT feeding systems may require cooling systems such as radiators to dissipate heat generated during operation. This ensures the transformers and other components operate within safe temperature limits, enhancing reliability and longevity.

Operational Principles

• Voltage Regulation: The auto transformer allows for voltage adjustment as needed to maintain consistent voltage levels along the railway line, ensuring optimal power delivery to trains.
• Rail Current Return: By connecting the neutral point to the rail, the AT system actively returns the rail current to the feeding line. This configuration minimizes electromagnetic interference and improves system efficiency.
• Power Absorption: The AT system enhances the ability of the railway tracks to absorb and distribute power effectively, accommodating varying loads and operational conditions of trains.

Advantages of AT Feeding System

• Efficiency: By utilizing an auto transformer and actively returning rail current, the AT feeding system reduces power losses and improves overall efficiency compared to traditional feeding systems.
• Reduced Interference: Minimizing inductive interference ensures clear communication signals for signalling and control systems alongside the railway tracks.
• Versatility: The AT feeding system is adaptable to different railway configurations and power requirements, supporting both conventional and high-speed rail networks.
• Reliability: Robust design and advanced protection systems ensure reliable operation under varying load conditions and environmental factors.
• Maintenance: Depending on the capacity, some AT systems may require minimal maintenance (e.g., smaller installations without radiators), reducing operational costs over the system's lifespan.

Applications

• AT feeding systems are essential for electrified railway networks worldwide, supporting efficient and sustainable transportation solutions.
• They are particularly crucial for high-speed railways like Shinkansen in Japan and other advanced rail networks where reliable and efficient power supply is critical.