5 MVA Transformers For Train Sets-88/2*1.22+2.36 KV | South Africa 2025

Precision power transfer for smooth acceleration: Traction Transformer.

01 General

1.1 Project Description

5000 kVA transformers for train sets was delivered to South Africa in 2025. The rated power of the transformer is 5000 kVA with ONAN cooling. The primary voltage is 88 kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 2*1.22+2.36 kV, they formed a vector group of Y/d±15°d11.

With a rated capacity of 5000kVA, the transformer operates at a primary voltage of 88kV and a secondary voltage configuration of 2×1.22kV (for traction) plus a 2.36kV tertiary winding (100kVA) dedicated to powering auxiliary transformers. It adheres to a 50Hz frequency standard, featuring copper windings (continuous disc-type for high-voltage and spiral-type for low-voltage) that ensure excellent electrical conductivity and mechanical robustness against fault currents. The ONAN (Oil Natural Air Natural) cooling system efficiently dissipates heat, complemented by thermal rise limits (≤50K for windings, ≤40K for top oil) to guarantee long-term stability even under heavy loads.

Notably, the transformer is built to withstand extreme load conditions: 2x load for 30 minutes, 3x load for 1 minute, and 3.5x load for 10 seconds (tripping at 4.25x load), making it compatible with twelve-pulse rectifier units. Equipped with an NLTC (No-Load Tap Changer) with ±2×2.5% voltage regulation (lockable for safety), it accommodates voltage fluctuations (±5% normally, -15% in special cases) and minimizes harmonic interference. Its robust design includes a ≥6mm steel tank (16mm base plate), fully insulated windings, and components like gas relays, overload thermal relays, and surge arresters to ensure operational safety.

Adaptable to harsh environments (altitude 0-1800m, temperature -10℃ to +55℃, 10%-90% relative humidity, heavy pollution), this traction transformer combines reliable performance, durability, and safety features, making it an ideal solution for South Africa’s railway traction power needs.

1.2 Technical Specification

5000kVA transformers for train sets specifications type and data sheet

1.3 Drawings

5000 kVA transformers for train sets diagram drawing and size.

02 Manufacturing

2.1 LV Bushing

The low-voltage (LV) bushing is a critical insulating feedthrough device that provides a secure, sealed passage for the transformer’s low-voltage winding leads to exit the tank. It is designed to safely conduct high current from the internal windings to the external traction network cables while maintaining excellent electrical insulation against the grounded tank. Constructed with a porcelain housing, it features a central copper conductor and is filled with insulating material. Its robust design ensures reliable performance under the mechanical vibrations and thermal cycles characteristic of railway operation, making it a vital interface for power output.

2.2 Tertiary Bushing

The traction transformer includes a dedicated delta-connected tertiary winding, typically rated for auxiliary power supply. This low-voltage winding, often created via a tap from the main secondary winding or as a separate coil, provides an isolated three-phase source. It is brought out through individual bushings to specifically feed auxiliary transformers, such as those rated for 100 kVA at 2.36 kV, which power onboard auxiliary loads.

2.3 HV Bushing

The HV bushing of the 5MVA traction transformer is designed for 88kV operation, featuring a minimum diameter of 19mm to ensure sufficient mechanical strength for external connections. With the live part’s total height from the ground not exceeding 2.7m (matching the on-site high-voltage busbar height), it adopts full insulation and is suited for areas with severe lightning strikes (compatible with surge arresters installed between the HV bus and substation grounding). It provides reliable insulation and connection for the high-voltage side while meeting the harsh environmental and operational requirements of the traction system.

2.4 Marshalling Box

The marshalling box of this traction transformer acts as a centralized auxiliary electrical interface unit, encased in a robust metal enclosure with a latching access door. Its interior houses multiple terminal blocks, compact control components (such as small relays or protection modules), and a built-in light to ease on-site maintenance work. Boasting an IP55 protection rating to withstand harsh traction-site conditions (including heavy pollution, fluctuating temperatures, and varying humidity), it incorporates corrugated hoses at the bottom for sealed, organized cable routing, while internal labeling helps simplify wiring identification. This unit centralizes the transformer’s control, signal, and auxiliary circuit connections, securing reliable electrical contact while streamlining upkeep-aligning with the rigorous operational demands of railway traction systems.

2.5 Hot-Dip Galvanized Radiator

The hot-dip galvanized radiator of the transformers for train sets is a core cooling component, featuring a durable hot-dip galvanized coating that grants strong corrosion resistance-ideal for withstanding harsh traction-site conditions (heavy pollution, temperature swings, and high humidity). Built as a finned structure to enhance heat exchange efficiency, it pairs with the transformer’s ONAN cooling system to dissipate heat from windings and top oil, keeping temperatures within safe operational limits. Its robust galvanized construction also tolerates railway-related vibrations, ensuring steady, long-lasting cooling performance to support the transformer’s heavy-load operations.

2.6 Oil Drain Plug

The oil drain plug for transformers for train sets is a critical accessory, usually made of cast steel or brass, mounted on the lower part of the transformer tank. It adopts threaded connection for stable installation and is equipped with a sealing ring to prevent transformer oil leakage. Primarily used for controlled oil drainage during maintenance (e.g., oil replacement, inspection) and safe oil sampling, it often has anti-theft structures-such as a cylindrical body with a wave-shaped special hole and central boss (needing a dedicated tool to operate) or a lock ring with padlock-to avoid unauthorized access. Compatible with transformer oil, it works within -20°C to 110°C and under nominal pressure ≤1.6MPa.

03 Testing

This test measures the insulation integrity of the windings by applying a DC voltage between each winding and earth, as well as between isolated windings, using a megohmmeter. The measured resistance value, often in the range of hundreds or thousands of megohms, indicates the quality and dryness of the solid insulation. The trending of results and the polarization index (PI) or dielectric absorption ratio (DAR) are critical for assessing insulation condition, helping to detect contamination, moisture ingress, or degradation in accordance with standards such as IEC60076.

04 Packing and Shipping

05 Site And Summary

In conclusion, the traction transformer stands as a critical and robust component within railway electrification systems. Its reliable operation is ensured through a combination of rugged design, high-quality materials, and stringent manufacturing standards, enabling it to withstand the demanding conditions of traction service-including thermal cycling, mechanical vibrations, and electrical stresses. Proactive and predictive maintenance, supported by diagnostic tests such as insulation resistance measurements and oil analysis, is fundamental to maximizing its service life and preventing failures. Ultimately, the performance and health of the traction transformer are paramount for guaranteeing the safety, efficiency, and continuous availability of electric rail transportation.