From Handcraft to High-Tech: How Has Transformer Manufacturing Evolved Over a Century?

Introduction

The transformer is often called the workhorse of the electrical grid. It has no moving parts, requires minimal maintenance, and can operate reliably for decades. But behind this apparent simplicity lies a manufacturing process that has evolved significantly over the past century.

From core cutting to insulation drying, each stage of production directly determines a transformer's performance, efficiency, and service life. This article offers a concise look at how transformers are built—and what makes the difference between a unit that lasts twenty years and one that lasts forty.

Chapter One: Core Manufacturing—The Magnetic Heart

The iron core is the magnetic circuit of a transformer. Its quality affects no-load losses, noise levels, and reliability.

Cutting Technology. Modern cores are made from grain-oriented silicon steel. Today's CNC cutting lines achieve positioning accuracy of 0.02 mm and exceed 300 cuts per minute—a significant advance from the manual processes of the 1970s.

Stacking Methods. Traditional manual stacking has given way to automated processes. The embedded yoke technique, for example, saves time by stacking the core column before inserting the lower yoke.

Joint Design. Multi-step joints now replace single-step designs, reducing no-load losses by over 15% and lowering noise by 3 to 4 decibels.

Material Evolution. Steel thickness has dropped from 0.35 mm to 0.20 mm, reducing eddy current losses. Cold-rolled grain-oriented steel remains the mainstream choice for its magnetic properties.

Chapter Two: Winding Manufacturing—The Electrical Circuit

Windings carry current and generate the magnetic field. Their construction directly impacts load losses and short-circuit strength.

Winding Configurations. Early cylindrical windings were hand-wound. Today, modular assembly integrates winding, shaping, and fitting for better consistency. Low-voltage coils increasingly use foil windings, which offer better space utilization and short-circuit performance.

Conductor Materials. Copper provides high conductivity and strength at higher cost. Aluminum is lighter and cheaper but requires larger cross-sections. The insulating enamel must maintain strong adhesion and heat resistance.

Dry-Type Innovations. For resin-cast transformers, new methods allow winding and casting long coils as single units—eliminating the mechanical vulnerabilities of joining separately cast sections.

Chapter Three: Insulation Processing—The Protection System

The insulation system determines a transformer's long-term reliability.

Processing Equipment. Insulation components were once cut manually. Today, gantry CNC machining centers cut, mill, and drill insulation board with millimeter precision.

Critical Materials. High-voltage insulation pressboard was historically a bottleneck material. Domestic manufacturers now produce it self-sufficiently, ending dependence on imports. Supporting materials—insulation paper, blocks, molded components—have formed complete supply chains.

Chapter Four: Drying and Oil Treatment—Core Processes

Moisture is the enemy of insulation. Removing it is critical.

Vapor-Phase Drying. Introduced from Switzerland in the 1980s, this technique uses kerosene vapor under vacuum to dry the transformer assembly. It reduces moisture content below 0.5%, ensuring long-term stability.

Oil Treatment. Transformer oil must be purified. Vacuum spray atomization removes gas and moisture effectively. Treated oil must meet strict standards for breakdown voltage, dielectric loss, and moisture content.

Low-Frequency Heating. A newer field technique circulates current through windings to generate heat internally, drawing moisture out under vacuum. It can reduce paper insulation moisture from 3% to under 1% in eight days—far faster than traditional methods.

Chapter Five: Breakthrough—Superconducting Reactors

In February 2026, the world's first 10 kV/1 Mvar air-core annular superconducting shunt reactor was commissioned in Shanghai.

Technical Advantages. Using superconducting materials with zero resistance and high current capacity, it achieves:

• Footprint under 6 square meters (60% reduction)
• Noise below 60 decibels
• Near-zero stray magnetic field

Application Value. Installed in a central Shanghai substation serving 22,000 households, it solved reactive power imbalance issues and improved voltage stability. The technology required two years of development, overcoming challenges in cryogenic insulation and cooling control.

Outlook: Where Manufacturing Is Headed

Three trends define the future:

Digitization. Digital twins now simulate manufacturing processes before production begins, optimizing quality and efficiency.

Precision. Automation continues to improve consistency across core stacking, winding, and insulation processing.

New Materials. Amorphous alloys, vegetable oil insulation, and superconducting materials are moving from research into practical application.

Conclusion

Transformer manufacturing has evolved from manual craft to precision engineering. From core cutting to insulation drying, each process improvement extends service life and enhances reliability.

For those in the industry, understanding these processes offers practical value: it helps differentiate suppliers, interpret specifications accurately, and address client questions with authority. The global position of Chinese transformer manufacturers rests on complete supply chains and continuously refined manufacturing techniques. Understanding these foundations enables better appreciation of both the product and the market.