Discussion on Construction Techniques for the 20 kV Power Supply System in High-Speed Railways

1. Project Overview
This project involves the construction of the new Jakarta–Bandung High-Speed Railway, with a mainline length of 142.3 km, including 76.79 km of bridges (54.5%), 16.47 km of tunnels (11.69%), and 47.64 km of embankments (33.81%). Four stations—Halim, Karawang, Padalarang, and Tegal Luar—have been constructed. The Jakarta–Bandung HSR mainline is 142.3 km long, designed for a maximum speed of 350 km/h, with a double-track spacing of 4.6 m, including approximately 83.6 km of ballastless track and 58.7 km of ballasted track. The traction power supply system adopts the AT (Autotransformer) feeding method. 

External power supply uses a voltage level of 150 kV, while the internal power distribution system uses 20 kV. The catenary wrist arms and positioning devices for the high-speed railway adopt China’s standardized and simplified design. China Railway Electrification Bureau is responsible for material procurement, construction of the entire power and traction power supply system for the Jakarta–Bandung HSR in Indonesia, as well as the external power connection portion funded by provisional sums.

2.20 kV Distribution Substation Design Scheme
2.1 20 kV Main Electrical Connection and Operating Mode
The 20 kV main busbar adopts a single-busbar configuration segmented by a bus-tie circuit breaker with automatic bus transfer. A 20 kV through-feeder bus section is provided, which, after passing through a voltage regulator, feeds out the 20 kV comprehensive load through-feeder line and the 20 kV primary through-feeder line. The neutral point of the voltage regulator is grounded via a small resistor, and no bypass switch is installed for the voltage regulator. 

Under normal operation, both power sources supply simultaneously with the bus-tie circuit breaker open. If one power source fails, the incoming circuit breaker on the de-energized side opens, and the bus-tie circuit breaker automatically closes, allowing the other power source to carry the full substation load. A reactive power compensation device is installed on the 20 kV through-feeder bus section, ensuring the power factor on the incoming side of the substation is no less than 0.9 after compensation.

2.2 Layout Plan
All distribution substations are co-located with station-area operational and living buildings on the ground floor, except for the Tegal Luar EMU Depot substation, which is independently built as a single-story structure. No cable interstitial floors are provided. The ground floor includes rooms for the voltage regulator (for primary and comprehensive through-feeders), reactive power compensation, neutral grounding equipment, communication machinery, spare parts storage, high-voltage switchgear, control room, tool room, and rest area. Cables within the substation are laid in cable trenches. 

Connections between the voltage regulator room, reactive power compensation room, neutral grounding equipment room, and the high-voltage room are made via pre-embedded conduits. Located within the station area, the substation does not have dedicated external access roads or fire lanes. An outdoor integrated utility trench is provided, equipped with cable supports; incoming and outgoing cables are routed through this trench, with power and low-voltage/control cables laid on opposite sides of the trench. Other sections use cable trenches and conduit installations.

3.Construction Preparation

• Site Investigation: Prior to construction, the contractor shall conduct a site survey based on approved design documents and relevant data, and prepare a site investigation report covering terrain, geology, road transport, equipment building conditions, and integrated utility trench routing.

• Construction Drawing Verification: The contractor shall verify approved construction drawings on-site and confirm their accuracy before use. Any discrepancies must be promptly reported to the client, designer, and supervising engineer for resolution.

• Based on the survey and verified drawings, the contractor shall develop a detailed implementation plan and work instruction manual for the distribution substation, clearly defining process standards, quality control requirements, and interface needs for critical procedures, and conduct named QR-code-based technical briefings.

• BIM Optimization: During the early construction phase, BIM technology shall be used to simulate equipment installation and cable routing in the 20 kV distribution substation. This enables optimized layout of equipment and trench/pipeline arrangements within the building, simulated cable routing in indoor and outdoor cable trenches, optimized cable pathways, and precise determination of support bracket locations. BIM’s visualization and simulation capabilities help avoid spatial conflicts during construction and improve efficiency.

4.Process Detail Optimization
4.1 Cable Trench Layout in Distribution Substation
The substation is a single-story structure, and branch cable trenches for individual equipment rooms are eliminated. Between the foundations in the voltage regulator room, reactor room, and small-resistor grounding room and the high-voltage/control rooms, pre-embedded steel conduits are used, extending into the high-voltage room cable trench up to the height of the second-level cable support from the bottom. To facilitate cable pulling, the pre-embedded conduit between the outdoor utility trench and the high-voltage room cable trench is optimized into a trench form, with wall-penetration plates installed at wall crossings.

4.2 Busbar Installation in Voltage Regulator Room
The original single-layer horizontal cable termination support bracket in the voltage regulator room has been optimized by adding angled steel bracing beneath the horizontal bracket to enhance stability and prevent shaking. Cables enter the voltage regulator from the top, with brackets installed at a height of 2,500 mm. The shield layer and armor of high-voltage cable terminations are separately grounded.

 All structural supports are connected to the main grounding conductor using flat or round steel bars. Copper busbars connect the cable terminations to the voltage regulator terminals, protected by cross-linked irradiated heat-shrink tubing with phase-color markings. For operational monitoring, an L-shaped stainless-steel mesh barrier with a stainless-steel maintenance door (equipped with an electromagnetic lock that only unlocks when the high-voltage switch is open) is installed. The barrier and door are positioned to ensure personnel safety and maintain required live-part clearances.

4.3 Cable Support Installation
BIM-based cable pre-laying simulation enabled segregated routing: power source side 1, power source side 2, primary through-feeder side, and comprehensive through-feeder side are laid on separate sides of the trench, preventing a fault on one power line from damaging the other. Cable bending radii are respected, and precise positioning of each cable on supports determined the optimal support type and location.

 BIM collision detection adjusted support heights to avoid cable crossovers. All horizontal rungs of supports are aligned on the same plane, with center deviations ≤5 mm. Supports are fixed to pre-embedded steel plates on trench walls, with the bottom of supports ≥150 mm above the trench floor. In the integrated utility trench, cable supports are grounded using 40 mm × 4 mm flat steel, with two grounding leads connected to the integrated grounding system.

4.4 Cable Laying Construction

• Cable Arrangement Principle: Cables of different voltage levels shall be arranged from top to bottom in the order of high-voltage power cables, control cables, and signal cables. Cables of different classifications or the two circuits of primary loads shall not be placed on the same support level.

• Design Refinement: Based on drawings, cable laying techniques allow deeper design refinement, enabling a complete and systematic construction plan that ensures smooth workflow integration and enhances safety and quality control.

• Traction Force Calculation: Traction machines are set at the endpoint, with cable feeders placed approximately every 1 m. Based on experience, an additional 10 cm is added at bends for traction force calculation.

• Site Inspection: Before laying, inspect equipment installation conditions. Ensure traction force remains below the cable’s allowable tensile strength. Conduct safety checks on cable laying machinery and survey the site to confirm cable reel placement; adjust immediately if standards are not met.

• Cable Laying Execution: Prior to laying, prepare labels and numbering based on drawings by qualified technicians. On-site supervision ensures correct cable routing and model usage. During mechanical laying, cables must show no armor flattening, twisting, or sheath damage. Use a crane to position the cable reel, supported by a dedicated payout stand to allow top-end unwinding and prevent ground friction. Install cable pulling grips on terminations before traction. Qualified technicians must supervise equipment operation and feeder machine placement: a main traction machine at the endpoint, feeders spaced 80–100 m apart, and large-radius sheaves at bends.

• Cable Fixing: After laying, fix cables at start/end points and both sides of bends, with fixing intervals of 5–10 m. Apply “lay one, tie one” binding principle and re-secure cables from the start point backward. For cables on trays, hang identification tags at both sides, bends, and intersections; on straight sections, tags every 20 m. Tags must uniformly display cable number, specification, start/end points, and voltage.

• Cable Circuit Inspection: After laying, inspect the entire cable circuit, associated components, and facilities. Verify tag accuracy, check for missing/wrong installations, and confirm quality compliance. To ensure safe operation:

• Install partitions between AC/DC cables or circuits of different voltages when not sharing a tray;

• Ensure all trench covers are in place and trenches are free of obstructions and water;

• Perform insulation withstand and leakage current tests per standards;

• Verify terminal alignment and grid compatibility during acceptance.

4.5 Fire-Retardant and Fireproofing Measures
All penetrations between fire compartments, building entries, floor slabs, and openings beneath HV/LV cabinets must be fire-stopped. Fire-stopping materials must comply with Indonesian standards for performance, test methods, general technical specifications for cable fire-retardant coatings, and technical requirements for flame-retardant cable wraps. Flame-retardant cables are used indoors. Non-flame-retardant cables entering the substation must be wrapped with flame-retardant tape or coated with fireproof paint.

5. Integrated Construction and Maintenance
During construction, operation and maintenance units were involved early to align construction and maintenance standards, laying the foundation for a high-quality, aesthetically pleasing, and eco-friendly HSR. On one hand, close coordination with the taking-over entity during design briefings, specification reviews, and technical liaison meetings helped refine process standards and equipment/material performance requirements based on operational experience. On the other hand, during construction—while meeting design and code requirements—processes were optimized from an operational safety and maintainability perspective, including improvements to cable trenches, cable maintenance access, junction boxes, grounding, protective mesh barriers, and signage, thereby enhancing operational safety and physical quality.

6. Conclusion
In summary, construction technologies for HSR power systems continue to advance, with more engineers applying integrated concepts to HSR projects. Upgrades in electromagnetic technology, rapid optimization of BIM, and improved early-warning systems all support the development of HSR’s “Four-Electrics” (power, signaling, telecom, and traction) integration. This paper aims to provide meaningful insights for the further advancement of these technologies.