Enhancing Indian Railways: The 2x25kV PSI System for 160 km/h Speed Potential

Enhancing Indian Railways: The 2x25kV PSI System for 160 km/h Speed Potential

As Indian Railways strives to enhance the speed and efficiency of its network, the implementation of the 2x25kV Power Supply Installation (PSI) system stands out as a critical advancement. With a commitment to upgrading existing routes to support speeds of up to 160 km/h, the Ministry of Railways has outlined comprehensive guidelines to facilitate this transition.

The Need for Speed: Upgrading to 160 km/h

The impetus for this upgrade comes from a directive by the Railway Board, which highlighted the necessity of enhancing railway routes. Following a series of consultations and technical evaluations, the Research Designs and Standards Organisation (RDSO) has revised and finalized the guidelines to ensure the successful implementation of these upgrades.

Increased Capacity

• High-Speed Rail: 2x25 kV is essential for high-speed rail lines, supporting speeds above 250 km/h.
• Heavy Freight: This system can handle the heavy loads of modern freight trains more effectively than lower voltage systems.

Improved Efficiency

• Reduced Transmission Losses: Higher voltage systems reduce energy losses over long distances, making them more efficient.

Enhanced Reliability

• Redundancy: The dual 25 kV system provides a level of redundancy, increasing reliability and minimizing downtime.
• Stability: More stable power supply supports modern, sensitive signaling and communication systems.

The 2x25kV System: A Technical Overview

In the 2x25kV system, power is supplied from the Traction Sub Station (TSS) at 50kV and utilized at 25kV through the use of Auto-Transformers (AT) of adequate capacity. This system includes an additional conductor, known as the feeder wire, which is similar to the return conductor in traditional systems. The center point of the Auto-Transformer is connected to the earth/rail, facilitating +25kV voltage between the Overhead Equipment (OHE) and the rail, and -25kV between the earth/rail and the feeder wire. This arrangement allows for higher efficiency and greater power supply over long distances.

Why the 2x25kV System?

The choice of the 2x25kV system is rooted in its global recognition as the optimal solution for high-density routes requiring substantial power. This system feeds power at 50kV from the Traction Sub Station (TSS) and utilizes it at 25kV through auto-transformers, thus minimizing voltage drops and enhancing efficiency. The key advantages include:

• Reduced Voltage Drop: For a given spacing of traction substations, the 2x25kV system experiences less voltage drop, making it ideal for high-power requirements.
• Increased Efficiency: The system can handle larger power demands efficiently, supporting the operational needs of modern, high-speed trains.
• Global Standard: It is widely used internationally and has been adopted by the Dedicated Freight Corridor Corporation of India Limited (DFCCIL) for its reliability and effectiveness.

Implementation Strategy

To transition to the 2x25kV system, the RDSO has detailed the installation and commissioning of Traction Sub Stations (TSS), Sectioning and Paralleling Posts (SP), and Sub-Sectioning and Paralleling Posts (SSP) at strategic locations. This phased approach ensures that the system can support the increased speed potential without compromising safety or reliability.

Key Technical Specifications

Traction Substations (TSS), Sectioning and Paralleling Posts (SP), and Sub-Sectioning and Paralleling Posts (SSP):

• TSS: Equipped with auto-transformers and necessary switchgear to handle 50kV input and distribute 25kV output.
• SP/SSP: Function as sectionalizing points, enhancing operational flexibility and reliability by isolating sections in case of faults.

Scott and V-Connected Schemes:

• Scott Connected Scheme: Utilizes a two-transformer setup to manage load balancing and improve system stability. This scheme is particularly effective in mitigating phase unbalances and enhancing power quality.
• V-Connected Scheme: Employs a three-transformer configuration, simplifying the installation, while still providing adequate voltage regulation for medium to high-speed operations.

Integration with Existing Systems

The implementation plan includes a boundary Sectioning and Paralleling Post (SP) that acts as an interface between the existing 1x25kV and the new 2x25kV systems. This interface ensures seamless power transition and distribution across the upgraded and existing segments of the railway network. The proposed integration is designed to handle the increased load without overburdening the Auto-Transformers at the boundary posts.

1. Boundary SP Interface: Acts as a transition point between 1x25kV and 2x25kV systems, managing load distribution and voltage levels.
2. Extension of Feed: Allows extension from 1x25kV to 2x25kV and vice versa, with specific attention to the capacity of auto-transformers at the boundary, ensuring they can handle the expected loads without overloading.

The guidelines include specific technical instructions to ensure uniformity and efficiency across the upgraded routes. Some highlights include:

• Auto-Transformers: These are essential for managing the voltage levels and ensuring stable power distribution.
• Feeder Wires: These additional conductors are crucial for reducing voltage drops and enhancing overall system efficiency.
• Capacitor Banks and Reactors: To improve power factor and ensure efficient power usage, the installation of fixed type capacitor banks and reactors is recommended.

Key Components and Technical Data

Scott Connected Transformer Scheme:

1. Configuration and Function: The Scott connected transformer is designed to reduce voltage unbalance and improve power quality. It consists of two windings: the Main and Teaser windings, each feeding one side of the Traction Substation (TSS) independently at a 90-degree phase difference. This configuration is essential for minimizing unbalance at the point of common coupling with the utility. Typically, two Scott connected transformers are installed at a TSS, with one operational and the other on standby, ensuring continuous and reliable power supply.
2. Technical Specifications: Voltage Input: 220kV or 132kV, 3-phase, 50 Hz. Secondary Windings: Two windings providing output at 50kV with 90-degree phase difference. Power Ratings: 60/84/100 MVA (ONAN/ONAF/OFAF), delivering 30MVA power to each side of the TSS in ONAN mode.

V-Connected Transformer Scheme:

1. Configuration and Function: This scheme employs three single-phase transformers connected in an open delta arrangement. Two transformers operate simultaneously while the third remains on standby, providing redundancy and reliability. The system operates at a 120-degree phase difference, which is critical for maintaining system stability and power quality.
2. Technical Specifications: Voltage Input: 220kV or 132kV, 50 Hz. Secondary Windings: Connected to deliver an output voltage of 2x25kV. Power Ratings: Each transformer feeds 38/53/63 MVA (ONAN/ONAF/OFAF) ?power to either side of the TSS in ONAN mode.

Auto-Transformers:

• Auto-transformers are used extensively in both schemes to minimize voltage drop and reduce induced voltages on nearby telecommunication lines. The typical capacities are: 12.3 MVA at TSS and 8 MVA at SP/SSP in the Scott scheme. 16.5 MVA at SP/SSP in the V-connected scheme.

Advantages and Operational Philosophy

Scott Connected vs. V-Connected Scheme:

• Voltage Unbalance: The Scott connected scheme excels in minimizing voltage unbalance, making it the preferred choice in areas where this is a concern.
• Complexity and Cost: While the Scott connected scheme is more complex and costly, its benefits in terms of reduced voltage unbalance justify the investment. Conversely, the V-connected scheme is simpler and more economical, making it suitable for applications where cost is a significant factor.
• Maintenance: The Scott connected transformers require more complex maintenance compared to the simpler V-connected scheme, which further influences the choice based on operational considerations.

Spacing and Load Considerations:

• The spacing of TSS and switching posts (SP/SSP) is designed to optimize power delivery and system reliability: For two-line sections, the spacing is 60-70 km. For three-line sections, the spacing is 50-60 km. For four-line sections, the spacing is 40-50 km.

Future-Proofing the Rail Network

The adoption of the 2x25kV system is a significant step towards modernizing India's rail infrastructure. By upgrading to this advanced power supply system, Indian Railways can ensure a reliable, efficient, and scalable solution that meets current and future demands. This upgrade not only supports the goal of achieving higher speeds but also enhances the overall safety and reliability of the rail network.

Conclusion

The 2x25kV PSI system represents a significant advancement in railway electrification, offering improved power quality, operational flexibility, and reliability. The choice between Scott and V-connected transformer schemes provides railways with options to tailor their infrastructure to specific operational needs and constraints. As we continue to push the boundaries of railway technology, these innovations will play a crucial role in shaping the future of high-speed rail transport.

For more detailed insights and implementation strategies, the full guideline on the 160 kmph PSI system is available for reference. Let's continue to innovate and drive our railways towards a more efficient and sustainable future.