5 MVA Model Railway Transformer-66/1.22 KV | South Africa 2025

Traction Transformer: Energizing Future Mobility.

01 General

1.1 Project Description

5 MVA traction transformer was delivered to South Africa in 2025. The rated power of the transformer is 5000 kVA with ONAN cooling. The primary voltage is 66 kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 1.22 kV, they formed a vector group of Y/d±15°d11.

Structurally designed for durability, the model railway transformer adopts a free-breathing configuration with a silicone grain breather to maintain oil quality, while its bolted tank cover enhances sealing performance. The galvanized radiators not only provide efficient heat dissipation but also offer excellent corrosion resistance, complementing the ONAN (Oil Natural Air Natural) cooling method that guarantees reliable operation under continuous load. Both high-voltage and low-voltage windings are crafted from copper, delivering superior electrical conductivity, minimal energy loss, and long-term operational stability.

In terms of performance, the transformer exhibits impressive efficiency-reaching up to 99.37% at 1.0 power factor and 99.22% at 0.8 power factor (at 75℃)-with low iron loss (6000 Watts) and full-load copper loss (25400 Watts at 75℃), resulting in a total load loss of 31400 Watts. Its full-load impedance stands at 8.15% (reactance: 8.13%), and the voltage regulation is optimized to 0.51% (1.0 PF) and 5.3% (0.8 PF) at 75℃, ensuring precise voltage control. With winding temperature rise limited to 50℃ and top oil temperature rise to 45℃, the transformer effectively mitigates thermal stress, extending its service life and meeting the rigorous requirements of traction power supply systems for safety, efficiency, and consistency.

1.2 Technical Specification

5000kVA traction transformer specifications type and data sheet

1.3 Drawings

5000 kVA traction transformer diagram drawing and size.

02 Manufacturing

2.1 Oil Conservator

The oil conservator is a sealed expansion tank connected to the main tank, designed to accommodate the natural expansion and contraction of the insulating oil due to temperature changes during operation. By maintaining a constant oil level and minimizing the oil’s exposure to air, it effectively prevents oxidation and moisture ingress. This crucial function ensures the long-term stability of the oil’s dielectric properties, safeguards the internal insulation, and significantly enhances the overall reliability and service life of the transformer.

2.2 Winding Temperature Indicator

The Winding Temperature Indicator (WTI) is a critical monitoring device for a traction transformer. It simulates the hottest spot temperature within the winding, which is higher than the measured top-oil temperature. Using a sensor bulb in the oil and a matched heating element connected via a capillary tube, the WTI accurately reflects the real thermal condition of the windings. It provides vital temperature readings and typically triggers alarms and, if necessary, trip commands to prevent insulation degradation and ensure the transformer operates reliably within its safe thermal limits.

2.3 Breather

The breather, or moisture absorber, is an essential protective device for a traction transformer. Mounted on the conservator’s air pipe, it contains a charge of silica gel desiccant. As the transformer breathes due to oil expansion and contraction, all incoming air is drawn through this breather. The silica gel actively absorbs moisture from the air, preventing it from entering the oil conservator and contaminating the insulating oil. This crucial function protects the transformer’s internal insulation system from degradation, ensuring dielectric strength and long-term operational reliability.

2.4 Terminal Box

The terminal box is a secure enclosure mounted on the traction transformer’s tank, housing the external electrical connections for the high-voltage and low-voltage windings. It provides a protected interface where insulated bushings terminate, and cables from the railway’s power system are connected. Its primary functions are to ensure safe, reliable electrical connections, protect the terminals from environmental factors like moisture and dust, and offer vital safety barriers for personnel during operation and maintenance, thereby ensuring the overall electrical integrity and safety of the transformer.

2.5 Hot-Dip Galvanized Radiator

The hot-dip galvanized radiator is the core cooling component of a model railway transformer. It consists of a series of finned panels or tubes that provide a large surface area to dissipate heat from the insulating oil into the surrounding air. The key feature is its hot-dip galvanized steel surface, which provides exceptional corrosion resistance. This robust protection is crucial for ensuring long-term structural integrity and optimal heat transfer efficiency, especially when the transformer operates in harsh or humid environments, thereby guaranteeing stable and reliable performance.

2.6 Active Part Drying

The active part drying is a critical manufacturing process for the traction transformer’s core-and-coil assembly (active part). It involves removing residual moisture from the cellulose insulation (paper and pressboard) and the core laminations through controlled heating under high vacuum. This rigorous process ensures the insulation achieves an extremely low and stable moisture content, which is fundamental for establishing high dielectric strength, preventing partial discharges, and guaranteeing the transformer’s long-term reliability and operational lifespan under demanding railway conditions.

03 Testing

The Full-Wave Lightning Impulse Test is a rigorous high-voltage type test applied to the line terminals of a traction transformer. It simulates a severe lightning strike by applying a standard 1.2/50 µs voltage impulse. This test verifies the integrity and strength of the main insulation system, particularly the windings and bushings, under extreme transient overvoltage conditions. Passing this test is crucial to prove the transformer’s ability to withstand real-world lightning surges, ensuring reliable protection for the railway power supply system.

04 Packing and Shipping

4.1 Packing

4.2 Shipping

05 Site And Summary

At SCOTECH, our model railway transformer are meticulously designed and manufactured to deliver uncompromising performance, exceptional reliability and extended service life. They are perfectly tailored to meet the rigorous operational requirements of high-speed railways, urban metros and other electrified rail transit systems. Adhering to the principles of technological innovation, stringent quality control and customer-centricity, we strive to be your most trustworthy partner for rail traction power solutions. We look forward to building long-term win-win cooperation with global customers, and jointly promoting the high-quality and sustainable development of the rail transit industry.