550kV/750kV UHV transformers

550kV/750kV UHV transformers utilize Siemens design software to comprehensively optimize and verify core, winding, active part, lead, and tank components, ensuring exceptional product performance. Superior process equipment, meticulous material selection, and efficient manufacturing result in transformers featuring compact size, light weight, low losses, low partial discharge, and low noise. The products offer superior quality, energy efficiency, environmental friendliness, convenient installation and maintenance, reliable operation, and effectively reduced operating costs.

The YT-500000/750GY transformer produced by our company has obtained KEMA certification, fully complying with international electrical equipment standards and technical specifications.

Featuring stable and reliable performance, our products are widely applicable to global power grid construction, large-scale AI computing centers, renewable energy (wind/solar) power plants, and high-end industrial parks, perfectly suited for core industries such as power engineering contracting, grid operation, and renewable energy development.

The structural characteristics of the components of the YT-500000/750GY are as follows:

1. Core: The core is a single-phase four-leg unequal magnetic reluctance type (MO type). The core cross-section is rationally optimized via computer programs. The core lamination utilizes high-permeability premium silicon steel sheets with a full-mitered step-lap design, ensuring favorable no-load performance while demanding high machining precision. The advanced two-piece lamination technology eliminates the need for upper yoke stacking, substantially lowering the exciting current and reducing no-load losses. The core legs and yoke frames are bound with epoxy resin non-woven fiberglass adhesive tape, ensuring safety and reliability. The core is completely insulated from the clamping components and grounded via a bushing on the tank to prevent the formation of short-circuit turns.

2. Windings: The interior of the windings adopts continuous shielding, equipped with transposed conductors and radial/axial oil ducts to ensure effective winding heat dissipation and lower winding temperature rise.

The high-voltage (HV) and low-voltage (LV) windings adopt a two-leg series structure, while the medium-voltage (MV) winding adopts a two-leg parallel structure, thereby reducing the external dimensions of the transformer and facilitating transportation. The windings are made of high-grade oxygen-free copper with low resistivity. The HV winding employs a wound-type plus inserted-shield continuous type, featuring improved potential gradient distribution at the end line segments under impulse voltage; the MV winding is an inserted-shield continuous type; and the LV winding is a single-helical type. The amp-turn distribution of the windings is optimized, enhancing radial support and axial compression forces. Windings processed through overall assembly and constant-pressure drying techniques significantly improve the transformer's short-circuit surge current withstand capability.

1. Insulation Structure: The main insulation structure of the transformer windings incorporates a thin paper tube embedded with a small-oil-gap insulation design. In this structure, the paper tube thickness is less than 4 mm, the oil gap width is less than 15 mm, and electrostatic rings are positioned at the winding ends to improve the impulse voltage distribution across adjacent sections and uniformize the electric field at the winding ends. The transformer utilizes a cylindrical pressing-screw device for clamping, which not only ensures continuous pressure on the windings but also prevents damage to the transformer caused by electromagnetic energy generated during short circuits. Both the jacking devices between the transformer and the oil tank, and the transformer positioning devices, undergo special treatment to achieve complete insulation between the transformer and the tank, avoiding the formation of short-circuit turns.

2. Leads: The high-voltage terminal is located at the center outlet, with two branch circuits connected in series via an equipotential pipe. The outlet utilizes Weidmann molded insulation components for insulation to ensure the quality of the leads.

3. Tank: The main tank features a bell-type structure, with the lower section being a box-type structure. The main tank body is reinforced with corrugated folded plates and braced with core reinforcements. Copper shielding and magnetic shielding layers are provided on the tank to effectively shield stray magnetic flux from entering the tank, reduce stray losses, and prevent local overheating.

750kV Class 260MVA ~ 380MVA Single-Phase Transformer

750kV Class 750MVA ~ 1140MVA Three-Phase Transformer

750kV Class 500MVA ~ 700MVA Single-Phase Three-Winding autoTransformer

550kV/750kV UHV Transformer Structural Diagram

（For structural illustration purposes only. Actual design details may differ）

1.HV Primary Bushing    2. Bushing Turret    3.Conductor Tip   4. MV bushing    5.Buchholz Relay   6.Conservator 7. Conservator Shutter Valve   8. On-load tap changer selector switch    

9. On-load tap changer(OLTC)   10.Voltage regulating winding   11.High and low voltage windings（Five-column three-winding）12.Voltage regulating winding  

13.Cooling System   14.Lead  Terminals   15.Lead Connectors 16.HV neutral bushing  17.Oil Tank   18. Oil Tank Base

500kV Oil-Immersed Single-Phase Double-Winding Off-Circuit Tap-Changing Power Transformer

500kV Oil-Immersed Three-Phase Double-Winding Off-Circuit Tap-Changing Power Transformer

FAQs about UHV Transformer:

1. What is the fundamental working principle of 500kV and 750kV UHV transformers?

500kV and 750kV ultra-high voltage (UHV) transformers operate on the core principle of electromagnetic induction. An alternating current flowing through the primary high-voltage winding creates a time-varying magnetic flux inside a high-permeability laminated silicon steel core. This magnetic flux induces an electromotive force in the secondary winding, allowing efficient step-up or step-down voltage transformation between massive power grids while minimizing energy losses over long-distance bulk power transmissions.

2. What are the primary application stages and fields for these UHV transformers?

These transformers are predominantly deployed in extra-high and ultra-high voltage power transmission stages, acting as core nodes in backbone regional power grids, long-distance inter-provincial bulk power links, and large-scale renewable energy integration hubs. They are vital for evacuating massive power outputs from mega-hydroelectric power stations, nuclear plants, and vast solar-wind energy bases to densely populated urban consumption centers located hundreds of kilometers away.

3. Why are 750kV transformers typically designed with single-phase configurations rather than three-phase?

Due to extreme physical size, massive unit weight, and strict transport clearance constraints imposed by roads and railways, 750kV UHV power transformers are usually manufactured as single-phase units. Three single-phase units are then banked together on-site to form a complete three-phase transformer bank. This modular approach eases logistical bottlenecks, simplifies heavy lifting, enhances structural reliability, and optimizes internal electromagnetic symmetry and thermal dissipation.

4. What are the critical insulation requirements for 500kV and 750kV transformer coils?

Because they operate under severe electrical stress, these transformers utilize advanced oil-paper insulation systems featuring thin paper tubes with minimized oil gaps and electrostatic shielding rings. The solid insulation must exhibit exceptional dielectric strength, maintaining moisture levels below 1% and oil contamination below 10 ppm. This setup ensures uniform electric field distribution and prevents partial discharges or breakdown under lightning and switching impulses.

5. How are thermal management and cooling handled in UHV transformers?

UHV transformers generate substantial heat from copper and core iron losses. To maintain safe operating temperatures, they utilize sophisticated cooling systems such as Oil Forced Air Forced (OFAF) or Oil Forced Water Forced (OFWF). Internal axial and radial oil passages within transposed conductor windings ensure unimpeded fluid circulation, preventing localized hot spots and keeping winding temperature rises well within thermal class safety thresholds.

6. What core manufacturing processes are critical for reducing no-load losses?

The magnetic core utilizes high-grade grain-oriented silicon steel sheets processed with full inclined joints and advanced step-lap lamination technologies. Cores are often designed with a multi-limb or unequal MO structure, where limbs and yokes are tightly bound with epoxy fiberglass tape. This precise mechanical construction drastically lowers the magnetic reluctance, minimizes core vibration, curtails excitation current, and significantly reduces overall no-load power losses.

7. What role does the vacuum drying and oil-impregnation process play during production?

Vacuum drying and oil impregnation are mandatory manufacturing stages to eliminate residual moisture and microscopic air pockets trapped within dense cellulose insulation matrices. Transformers undergo prolonged heat-cycle vacuum processing before being impregnated with ultra-pure, degassed transformer oil under deep vacuum. This process maximizes breakdown voltage limits, ensures absolute insulation integrity, and prevents catastrophic internal short circuits during live grid operations.

8. How do manufacturers protect UHV transformers against severe short-circuit electromagnetic forces?

During sudden grid faults, immense short-circuit currents generate radical electrodynamic forces capable of deforming windings. To resist this, UHV transformer windings undergo constant-pressure drying and integral assembly processes. They are structurally reinforced using high-density pressboard cylinders, heavy-duty clamping plates, and hydraulic or screw-jacking compression devices that permanently lock the windings in place against severe radial and axial forces.

9. How is stray magnetic flux managed within the massive steel transformer tanks?

High-capacity 500kV and 750kV units produce intense leakage magnetic fields that can induce eddy currents and cause dangerous localized overheating on conventional steel tank walls. To mitigate this, manufacturers line the interior walls of bell-shaped tanks with carefully positioned copper shields and electromagnetic magnetic shunts. These conductive and ferromagnetic paths safely absorb stray flux lines, drastically reducing stray load losses and protecting the structural shell.

10. What specialized testing procedures must these transformers pass before factory dispatch?

Prior to delivery, UHV transformers must endure rigorous factory acceptance testing (FAT) inside specialized high-voltage test laboratories. Essential diagnostics include lightning and switching impulse voltage tests, partial discharge measurement under high-frequency setups, temperature-rise verification, short-circuit withstand evaluations, and dissolved gas analysis (DGA) baseline checks to guarantee long-term field reliability under harsh grid conditions.