5 MVA Traction Transformers-132/1.22 KV | South Africa 2025

Traction Transformer - Power in Motion.

01 General

1.1 Project Description

5000 kVA traction transformer was delivered to South Africa in 2025. The rated power of the transformer is 5000 kVA with ONAN cooling. The high voltage is 132 kV with ±2*2.5% tapping range (NLTC), the low voltage is 2*1.22+0.635 kV, they formed a vector group of Y/d±15°d11.

Tailor-made for the harsh operating conditions in South Africa, the 5MVA traction transformer serves as the core guarantee for rail transit traction power supply systems, integrating precise parameter configuration and excellent environmental adaptability with high-reliability design and customized technical solutions to perfectly match the complex on-site operating requirements.

In terms of core parameters, the transformer has a rated capacity of 5000kVA, a primary voltage of 132kV, and a secondary side adopting 2×1.22kV dual delta-connected windings (compatible with twelve-pulse rectifiers, providing six-phase output), paired with a 0.635kV/150kVA tertiary winding (equipped with independent bushings to supply power to the auxiliary transformer). Operating at 50Hz, it uses high-conductivity copper for windings to ensure efficient and stable power transmission. The connection group is designed as Ydd±15°, with a 15° phase shift between the dual low-voltage windings, which effectively optimizes the power quality of the traction system while minimizing the impact of harmonic interference through special design.

Targeting the harsh on-site conditions in South Africa-including heavy pollution, voltage fluctuations (±5% under normal conditions, -15% under special circumstances), a wide temperature range (-10℃ to +55℃), high altitude (0-1800m), and relative humidity of 10%-90%-the product features a fully insulated winding structure, a fuel tank made of ≥6mm thick steel plate (16mm thick base plate), hot-dip galvanized anti-corrosion radiators, combined with a conservator with bladder and breather, achieving strong moisture resistance, corrosion protection, and insulation protection. It can withstand lightning impulse of HV/LV1/LV2 550/60kV and has sufficient mechanical strength to resist the impact of fault currents, ensuring stable operation under extreme conditions.

In terms of performance, the transformer adopts ONAN (Oil Natural Air Natural) cooling. The winding temperature rise does not exceed 65℃ under continuous full-load operation after reaching thermal equilibrium and stable temperature. It can easily cope with short-term overload challenges: the temperature rise is controlled within 70℃-100℃ under operating conditions of 3x load for 1 minute, 3.5x load for 10 seconds, and 2x load for 30 minutes, with automatic tripping protection at 4.25x load, balancing operational safety and overload flexibility. Key accessories include an NLTC off-circuit tap changer (±2×2.5% adjustment with padlockable function), a single-float gas relay (with alarm and trip contacts), a winding temperature indicator with ambient temperature compensation (set to trip at 115℃), and a terminal box with IP55 protection class. Additionally, the bushing height is optimized to match the on-site 2.7m high-voltage busbar installation requirements, with an observation window/manhole on the top for easy maintenance, and oil filter connection pipes reserved on the side of the fuel tank, comprehensively improving operational and maintenance convenience.

From the winding structure design (continuous disc-type for high voltage, spiral-type for low voltage) to material selection and load-bearing capacity, this traction transformer is fully customized for the particularities of traction power supply systems. It not only meets the compatibility requirements of twelve-pulse rectifiers but also provides independent guarantee for auxiliary power supply through the tertiary winding, making it an ideal traction power supply solution with anti-interference, harsh environment resistance, and high safety redundancy for the South Africa project.

1.2 Technical Specification

5000 kVA traction transformer specifications type and data sheet

1.3 Drawings

5000 kVA traction transformer diagram drawing and size.

02 Manufacturing

2.1 Core

The core of a traction transformers is constructed from laminated, high-permeability, low-loss materials-cold-rolled grain-oriented silicon steel. Designed to be robust and compact, it withstands the frequent impact loads and mechanical vibrations inherent in rail operation. The laminations are often assembled with fully lapped and staggered joints to minimize magnetic reluctance and no-load losses. Effective clamping and damping measures are integral to its design, ensuring a stable and efficient magnetic path for reliable voltage transformation and power transfer under demanding conditions.

2.2 Winding

The continuous winding of a traction transformers is usually made of copper enameled flat wire or continuously transposed conductor (CTC). It is wound in a continuous disc shape without inter-disc joints, featuring low AC loss and uniform heat dissipation; by optimizing insulation design to control voltage stress, it can also meet the mechanical strength requirements under working conditions like 3.5 times overload. This structure is commonly adopted for high-voltage windings, which can adapt to 12-pulse rectifiers, providing a stable magnetoelectric path for efficient energy conversion in traction systems while complying with full insulation requirements to ensure operational safety.

2.3 Tank

The tank is made of steel plates with a thickness of ≥6mm (the base plate thickness is 16mm), and its top cover is connected by bolts. The outer surface is painted gray with a paint thickness of no less than 125 microns. The interior of the tank is filled with transformer oil, which provides insulation and heat dissipation for the iron core and windings. It cooperates with detachable hot-dip galvanized radiators with paint to achieve cooling, and is connected to the white bladder oil conservator at the same time to ensure the transformer body is always immersed in oil. The main tank is equipped with one pipe with a faucet (with 50mm internal thread) on both the oil conservator side and the opposite side, which is used for connecting the oil filter and suitable for ground operation-one pipe is arranged at a high position, and the other at a low position (the low-position one can be combined with the oil drain valve if necessary). The tank is also equipped with protective devices such as a pressure relief valve, and needs to be compatible with bushings whose live parts are no more than 2.7m above the ground, so as to meet the operational requirements in areas with heavy pollution and severe lightning strikes in South Africa, as well as under the 3.5x load condition.

03 Accessories

3.1 Hot Dip Galvanized Radiator

This detachable radiator features a hot-dip galvanized base with an additional paint coating, is compatible with the traction transformer’s ONAN cooling system to assist in heat dissipation, and is designed to adapt to South Africa’s harsh operating conditions (heavy pollution, temperature range of -10~+55℃, and 3.5x load scenarios) while ensuring long-term corrosion resistance and structural stability.

3.2 Winding Temperature Indicator

The winding temperature indicator (regarded as an overload thermal relay) is designed to protect the traction transformer from overload, featuring a load-temperature (approximating the winding’s hottest spot temperature) correlation and ambient temperature compensation function; it is equipped with a trip contact set at 115℃ (based on 45℃ ambient temperature + 70℃ maximum temperature rise) and has electrical parameters of 110V DC and 6A, which is adaptable to the transformer’s harsh operating conditions such as 3.5x load to ensure safe operation.

3.3 Terminal Box

The terminal box of this traction transformer features an IP55 protection rating, effectively preventing dust ingress and low-pressure water splashing, and is engineered to adapt to harsh on-site conditions in South Africa (including heavy pollution, a temperature range of -10~+55℃, and 10%-90% relative humidity). It serves to protect internal electrical connections, ensuring reliable wiring and signal transmission for the transformer even under extreme operating conditions such as 3.5x load, thus safeguarding the equipment’s stable operation.

04 Testing

This 5000kVA 132/2×1.22+0.635kV traction transformers has completed a series of routine tests in accordance with relevant power transformer standards, including a 24-hour pressure tightness test at 30kpa with no leakage, insulation oil tests (dissolved gas and moisture content detection), insulation resistance, dielectric loss and capacitance measurements of the iron core and windings, voltage ratio and phase displacement verification, winding resistance, short-circuit impedance, no-load and load loss tests, ratio and polarity check of built-in current transformers, applied voltage test, induced voltage withstand test with partial discharge (PD) measurement, and auxiliary wiring insulation test. All test results comply with technical requirements, and the transformer is ultimately deemed qualified, capable of meeting its operational condition needs.

05 Packing and Shipping

06 Site And Summary

This 5000kVA 132/2×1.22+0.635kV traction transformer is designed and manufactured in strict compliance with relevant power transformer standards. It is adapted to the harsh on-site conditions in South Africa, including heavy pollution, severe lightning strikes, and a temperature range of -10~+55℃, boasting core characteristics such as 3.5x load withstand capacity, full insulation, and high mechanical strength. The design of key components and structures fully meets operational requirements. Verified through a series of routine tests, all indicators including sealing performance, insulation level, voltage ratio accuracy, and loss control comply with technical specifications, and the transformer is ultimately deemed qualified. Capable of stably adapting to 12-pulse rectifier units, this transformer provides efficient and safe energy conversion support for the traction system, fully satisfying the reliability and durability demands of on-site operation.