5.05 MVA Railway Transformers-132/2*1.22+2.36 KV | South Africa 2025

Engineered for the long haul: Precision Traction Transformer.

01 General

1.1 Project Description

5050 kVA traction transformer was delivered to South Africa in 2025. The rated power of the transformer is 5050 kVA with ONAN cooling. The primary voltage is 132 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°/d-15°/d.

Operating at 50Hz, the transformer has a primary voltage of 132kV and a secondary voltage of 2×1.22kV (for traction) plus a 2.36kV/100kVA tertiary winding (for auxiliary transformers). Copper windings (continuous disc for HV, spiral for LV) offer strong mechanical strength, withstanding 30-minute 2x, 1-minute 3x, and 10-second 3.5x overloads (tripping at 4.25x load).

Adapted to South Africa’s environment (0-1800m altitude, -10℃ to +55℃ temperature, 10%-90% humidity, heavy pollution), the transformer features a durable tank constructed from ≥6mm steel plate (16mm thick base) and galvanized radiators with protective paint, ensuring corrosion resistance and long-term reliability.

Equipped with a capsule conservator, moisture absorber, and monitoring devices, it maintains optimal insulation (LI60AC20kV for LV/tertiary windings).

Safety and operability are prioritized through a comprehensive suite of accessories: an off-load tap changer (±2×2.5% with lockable operation), gas relay with alarm and trip contacts, overload thermal relay (with temperature compensation and 115℃ trip setting), pressure relief valve, and IP55-rated terminal box. Compliance with strict dimensional constraints-such as live parts being 3950mm above ground and bushing height not exceeding 2.7m-ensures seamless on-site installation and compatibility with existing high-voltage busbars.

With full insulation on all windings, mechanical strength optimized for fault current resistance, and adherence to international quality standards, this traction transformer is ideally suited for high-reliability power supply in railway traction systems, industrial facilities, and other critical infrastructure projects, delivering efficient, safe, and consistent performance even in challenging environments.

1.2 Technical Specification

5050kVA traction transformer specifications type and data sheet

1.3 Drawings

5050 kVA railway transformers diagram drawing and size.

02 Manufacturing

2.1 Oil Conservator

The oil conservator, also known as the expansion tank, is a cylindrical vessel mounted above the main tank of a traction transformer. Its primary function is to accommodate the thermal expansion and contraction of the insulating oil. As the oil heats up during operation, it expands and flows into the conservator; as it cools, the oil level recedes. This system maintains a positive pressure and prevents air from entering the main tank. The conservator is equipped with an oil level indicator for visual monitoring and is connected to the main tank via piping. It incorporates a silica gel breather to dehydrate any air entering the space above the oil, thereby preserving the oil’s dielectric properties and preventing moisture ingress.

2.2 Hot-Dip Galvanized Radiator

The hot-dip galvanized radiator is a critical cooling component for railway transformers. Constructed from steel sheets formed into fin-type structures, it is submerged in molten zinc to create a robust, adherent coating. This galvanization provides exceptional corrosion resistance, essential for withstanding harsh outdoor environments, moisture, and contaminants encountered in railway applications. The radiators efficiently dissipate heat loss from the transformer, maintaining optimal operating temperature. Their durable zinc coating ensures long service life with minimal maintenance, directly contributing to the transformer’s reliability and operational availability.

2.3 Marshalling Box

The marshalling box of the railway transformers acts as a centralized wiring hub for the unit: it houses multiple terminal blocks (for organizing signal/power line connections), protective components (like breakers and relays), and labeled terminals. This compact enclosure streamlines wiring management, simplifies debugging and maintenance, and boosts operational safety by neatly consolidating circuit connections in a clearly identified setup.

2.4 Air Breather

The air breather is a vital accessory mounted on the oil conservator of a traction transformer. Its primary function is to prevent moisture from entering the transformer during the “breathing” cycle-when air is drawn in as the insulating oil cools and contracts. The breather typically consists of a transparent container filled with silica gel desiccant, which changes color (often from blue to pink) as it absorbs moisture from the incoming air. An integral oil seal or baffle system ensures all incoming air passes through the desiccant, effectively drying it. This process protects the insulating oil and solid insulation from degradation, thereby maintaining the transformer’s dielectric strength and operational reliability in varying environmental conditions.

2.5 Earthing Terminal For The Core

The earthing terminal for the core is a robust, corrosion-resistant external connection point on the transformer tank. Its sole function is to provide a permanent, low-impedance ground connection for the transformer’s magnetic core. By bonding the core laminations to the earth, it safely bleeds off any static charges or dangerous potentials induced by stray fluxes, preventing internal arcing and ensuring operational safety. This single-point grounding is essential for the reliable and secure performance of the traction transformer in the railway system.

2.6 Off-Circuit Tap Changer

The off-circuit tap changer of railway transformers is an unloaded-operation component: it adjusts winding turns (when the transformer is de-energized) to fine-tune output voltage, and consists of three-phase switches linked by a mechanical mechanism. Before energization, it is critical to verify the three-phase switches are synchronized-this involves checking their position indicators or mechanical linkages to confirm all phases sit at the same tap position, which avoids winding imbalance, local overloads, or equipment damage, ensuring accurate voltage regulation and safe operation.

03 Testing

Check of ratio and polarity of built-in current transformers is a routine test for the traction transformer (conducted at 8℃ oil temperature), targeting its built-in current transformers. It verifies that the nominal ratios (e.g., 50/1, 50/5 for Phase A) match the measured ratios across Phase A/B and different types (LR-132, LRB-132), confirms correct polarities (marked “- (correct)”), measures DC resistances (e.g., 0.3985Ω for Phase A’s LR-132), and checks that insulation resistances are ≥5GΩ-ensuring the current transformers meet parameter standards and support reliable current monitoring/protection for the traction transformer.

04 Packing and Shipping

05 Site And Summary

As the core power conversion component of rail transit systems, the railway transformers underpins the safe, efficient and stable operation of locomotives and EMUs. Engineered for rugged rail operating conditions, it delivers uncompromising performance, low loss and long-term reliability. We keep advancing design and manufacturing technologies to tailor traction transformer solutions that match the evolving needs of global rail transit, powering the smooth and sustainable journey of rail mobility worldwide.