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01 General
1.1 Project Description
5 MVA railway traction transformer was delivered to South Africa in 2025. The rated power of the special transformer is 5 MVA with ONAN cooling. The primary voltage is 132 kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 2*1.22+1.22 kV, they formed a vector group of Y/d+15°/d-15°/d, Yd11.
This railway traction transformer is designed for modern rail transit systems, combining excellent performance with multiple protection features. It is equipped with an off-load tap changer with an operating handle and lockable provision, ensuring convenient and safe operation. The transformer utilizes high-efficiency heat-dissipating radiators with hot-dip galvanizing and paint, enhancing its corrosion resistance. An oil conservator with a desiccant and oil level gauge allows real-time monitoring of the oil’s health status. The single-float gas relay, featuring alarm and trip contacts, responds swiftly to fault conditions. Overload thermal relays offer overload protection, featuring a load-temperature relationship and ambient compensation, with trip activation at specified temperatures. The device includes a pressure release valve to prevent pressure anomalies, adopts IP55-rated terminal boxes to withstand harsh environments, and includes current transformers for precise current monitoring. This transformer’s design ensures reliability and safety in railway and other traction applications.
1.2 Technical Specification
5 MVA railway traction transformer specifications type and data sheet
| Delivered to | South Africa |
| Year | 2025 |
| Type | Traction transformer |
| Standard | IEC60076 |
| Rated Power | 5000kVA |
| Frequency | 50HZ |
| Vector group | Yd±15°,Yd11 |
| Phase | 3 |
| Cooling Type | ONAN |
| Primary Voltage | 132 kV |
| Secondary Voltage | 2*1.22+1.22 kV |
| Winding Material | Copper |
| Impedance | 8.5% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5%@primary side |
| No Load Loss | 7.7kW |
| On Load Loss | 26.5kW |
1.3 Drawings
5000 kVA railway traction transformer diagram drawing and size.
02 Manufacturing
2.1 Core
| The core is made of high-quality silicon steel sheets, which have excellent magnetic permeability and low loss, ensuring high efficiency and stability. The laminated structure design reduces eddy current loss and further enhances insulation performance and energy utilization efficiency through the use of insulating materials between the layers. The core is designed in a closed-loop shape to form a closed magnetic circuit and enhance magnetic field utilization while considering heat dissipation performance to maintain an appropriate operating temperature under high loads, thereby prolonging service life. Additionally, the core is designed to reduce electromagnetic interference, ensuring stability without affecting surrounding equipment. Its assembly process is precisely engineered to ensure tight integration of components, minimizing mechanical vibrations and noise, and improving structural strength and stability. |  |
2.2 Winding
 | Connection: Yd ± 15° (The low-voltage winding and the tertiary winding are both connected in delta, with the capacity of the low-voltage tertiary winding being 100 kVA) All windings are fully insulated. High-voltage winding: Star connection Low-voltage primary winding: Delta connection Low-voltage secondary winding: The low-voltage secondary winding should be connected in delta, with the configuration comprising two independent delta windings, phase-shifted by 15°. There are a total of six phases in the secondary winding, each with an output voltage of approximately 1220 volts. The secondary winding should be designed to be compatible with a twelve-pulse rectifier unit. The high-voltage winding should use continuous disc windings, while the low-voltage winding should use helical windings. The transformer is required to be used in areas with severe lightning strikes. Lightning arresters should be installed between the high-voltage bus and the grounding of the substation. The neutral point of the main star winding does not need to be brought out. The transformer windings must have sufficient mechanical strength to withstand fault currents. |
2.3 Tank
| The fuel tank is made of steel plates with a thickness of ≥6mm, and the top cover of the fuel tank is connected by bolts. The transformer oil tank is grey, the oil pillow is white, and the paint thickness is at least 125 microns. On the main oil tank, there is one pipe with a faucet on the side close to the oil pillow and one on the opposite side, which is used to connect the oil filter. The height is suitable for ground operation, with one side at a higher position and the other at a lower position (if necessary, this side can be combined with the oil drain valve). The faucet has an internal thread of 50mm. |  |
2.4 Final Assembly
 | 1. Winding installation: Install the high-voltage winding on the core, paying attention to the winding layers, the number of turns and the connection method (such as star or Angle connection). Subsequently, install the low-voltage primary winding and secondary winding, ensuring that the phase and connection method of the windings are correct. Finally, install the low-voltage third winding to ensure that it meets the power supply requirements of the auxiliary transformer. 2. Hoisting and oiling of the live part: Hoist the live parts (windings and cores) of the transformer to the designated positions and ensure correct alignment. Install accessories such as lightning arresters, relays, terminal boxes, etc After the hoisting is completed, oil should be injected to ensure that the transformer is fully filled with oil inside to guarantee insulation and cooling. |
03 Testing
1. Routine test-Leak Testing With Pressure For Liquid-Immersed Transformers (Tightness Test)
2. Routine test-Measurement of dissolved gasses in dielectric liquid from each separate oil compartment except diverter switch
3. Routine test-Check Of Core And Frame Insulation For Liquid Immersed Transformers With Core Or Frame Insulation
4. Routine test-Measurement of voltage ratio and check of phase displacement
5. Routine test-Measurement of winding resistance
6. Routine test- Check of ratio and polarity of built-in current transformers
7. Routine test-Measurement Of D.C Insulation Resistance Between Each Winding To Earth And Between Windings
8. Routine test-Measurement of dissipation factor (tanθ) of the insulation system capacitances
9. Routine test-Determination of capacitances windings to earth and between windings
10. Routine test-Measurement of No-load Loss and Current
11. Routine test-Measurement of no-load loss and current at 90 % and 110 % of rated voltage
12. Routine test-Measurement of Short-circuit Impedance and Load Loss
13. Routine test-Full wave lighting impulse test for the line terminals .(LI)
14. Type test-Determination of sound level (IEC 60076-10) for each method of cooling for which a guaranteed sound level is specified
15. Special test-Measurement of frequency response (Frequency Response Analysis or FRA)
16. Routine test-Applied Voltage Test (AV)
17. Routine test-Induced Voltage Withstand Test with PD measurement. (IVPD)
18. Routine test- Auxiliary Wiring Insulation Test.(AuxW)
19. Routine test-Measurement of dissolved gasses in dielectric liquid from each separate oil compartment except diverter switch compartment.(After test)
20. Type test-Temperature-rise type test
21. Routine test-Measurement of dissolved gasses in dielectric liquid from each separate oil compartment except diverter switch compartment.(After test)
04 Packing and Shipping
4.1 Packing
| 1. Wrap the oil drain valve of the main body with something like cling film and stick a seal underneath to prevent it from being opened at domestic and foreign ports. 2. Protective measures are adopted for terminal boxes, accessory boxes and other accessories to prevent damage from impact during sea transportation. 3. Factory documents: Our company’s test report, our company’s transformer manual, and accessory manual. 4. After packaging, confirm the final size and make a packing list. 5. Two copies of each shipping mark should be printed and pasted on the upper left corner of the adjacent sides of the package. |  |
4.2 Shipping
 | Transporting a 5MVA transformer to Durban port under CIF (Cost, Insurance, and Freight) terms involves several steps. First, the transformer’s packaging must comply with maritime standards, and relevant documents such as the packing list, commercial invoice, and bill of lading should be prepared. Next, a suitable shipping company is selected, and arrangements are made for the safe loading of the transformer into a shipping container. During the maritime transport process, the carrier is responsible and provides insurance coverage for any transport risks. Upon arrival in Durban, timely customs clearance procedures should be completed, and specialized equipment used to unload the transformer. Finally, an inspection of the transformer’s appearance and functionality is conducted to ensure there was no damage during transport. Under CIF terms, the seller assumes all costs and risks associated with the transportation until the transformer safely reaches the destination port. |
05 Site And Summary
In conclusion, our railway traction transformer are engineered to meet the demanding needs of modern transportation systems, providing reliable performance and exceptional efficiency. With advanced technology and robust construction, these transformers ensure optimal energy management and enhanced operational safety for rail and metro applications. As a trusted partner in the industry, we are committed to delivering high-quality products that not only meet but exceed our customers’ expectations. Choose our traction transformers for a sustainable and efficient solution that powers the future of transportation.
