1. Definition and Core Principles

A high-voltage transformer is a static electrical device that elevates or reduces AC voltage through electromagnetic induction. Its primary function is to boost low-voltage electricity (e.g., 10 kV) generated by power plants to ultra-high voltages (above 110 kV) for long-distance transmission, then step it down to safe usage levels (e.g., 220 V) for end-users. This process relies on ​Faraday's Law of Electromagnetic Induction: when AC flows through the primary winding, it generates an alternating magnetic flux in the core, inducing an electromotive force (EMF) in the secondary winding. The voltage ratio strictly follows the ​turns ratio formula​ (U₁/U₂ = N₁/N₂). For example, if the primary winding has 1,000 turns and the secondary 10,000 turns, the output voltage increases tenfold.

2. Core Structural Analysis

(1)Core​
Constructed from laminated 0.23–0.35 mm thick high-permeability silicon steel sheets coated with insulating varnish to minimize eddy current losses. Modern cores adopt a "step-lapped" design, reducing magnetic resistance by 30% and no-load losses by 15% 

(2) Windings​

· ​Primary winding: Typically wound with twisted copper wire to withstand high voltages (up to 1,000 kV), featuring thin conductor cross-sections but insulation layers exceeding 5 mm.

· ​Secondary winding: Uses continuous twisted copper for low-voltage, high-current applications, with cross-sectional areas up to 10 times that of the primary.

(3)Cooling Systems​

· ​Oil-immersed: Transformer oil serves dual roles as insulation (dielectric strength ≥30 kV/mm) and coolant, maintaining oil temperatures below 85°C.

· ​Dry-type: Employs Nomex paper insulation with forced-air or SF₆ cooling, ideal for sensitive environments like subways and data centers 

3. Classification and Applications

In the ±800 kV UHVDC project on the Qinghai-Tibet Plateau, transformers operate at -40°C and 4,500 m altitude. Vacuum oil filling and nitrogen expansion compensation technologies prevent insulation oil solidification, ensuring stable grid performance 

4. Technical Challenges and Innovations

(1) Loss Control​
Modern transformers use ​amorphous alloy cores​ (1/5 the iron loss of silicon steel) and AI-driven smart voltage regulation, reducing no-load losses to <15 kW/10 MVA. State Grid’s latest standards mandate ≥98% efficiency for 110 kV transformers.

(2)Insulation Breakthroughs​
Epoxy resin vacuum impregnation achieves partial discharge levels below 5 pC. ±1,100 kV transformers feature segmented bushings with 7.2 m creepage distances.

(3) Smart Upgrades​
Integrated fiber-optic temperature sensors (±0.5°C accuracy), vibration monitors (10 kHz sampling), and AI algorithms enable >92% fault prediction accuracy. China Southern Power Grid has deployed digital twin systems in 2,000 transformers.

5. Maintenance and Safety Protocols

· ​Routine Testing: Insulation resistance tests every 3 years (standard >1,000 MΩ), winding DC resistance deviation <2%.

· ​Oil Chromatography: Monitor H₂ and CO levels; total hydrocarbon increases >10% trigger immediate shutdowns.

· ​Lightning Protection: Install 10 kA arresters with ≤4 Ω grounding resistance.

6. Future Trends

With rising renewable energy adoption, high-voltage transformers are evolving toward ​modular designs​ (60% shorter installation times), ​multi-terminal interconnections​ (supporting parallel VSC-HVDC operations), and ​carbon footprint tracking​ (40% lifecycle emission reductions). By 2030, the global market is projected to exceed $80 billion, with China accounting for over 45% of demand.