The development of steam turbine generators, including gas turbine generators and combined-cycle gas turbine generators, represents a remarkable journey in the evolution of the global power industry. Over more than 100 years, the single-unit capacity of generators has increased from several hundred kilowatts to more than one million kilowatts, driven by continuous advances in science, engineering, and manufacturing technologies.

The growth of generator capacity has been closely linked to the rapid development of industrial production, agriculture, and increasing electricity demand worldwide. The expansion of power grids has further accelerated the development of large-capacity generating units, which play an important role in improving grid stability and reliability.

In addition, under market-oriented energy systems, improving power generation efficiency and reducing operating costs have become key drivers for the development of high-capacity and high-efficiency generator units.

Today, advanced steam turbine generator technologies have achieved significant breakthroughs:

• The capacity of 4-pole generators for nuclear power plants has reached 1600 MVA;

• The capacity of 2-pole steam turbine generators has reached 1200 MW;

• Gas turbine generators and combined-cycle power generation systems continue to develop toward larger capacity and higher efficiency.

Key Factors Driving Generator Capacity Growth

The apparent power output of a generator is closely related to several important parameters, including:

• Effective length of the stator core;

• Inner diameter of the stator core;

• Stator linear load;

• Air-gap magnetic flux density;

• Synchronous speed.

The generator capacity can also be considered proportional to the length and diameter of the rotor.

The size of the rotor is directly affected by the performance of metallic materials, as well as the capabilities of large-scale forging and manufacturing technologies. Therefore, increasing generator capacity requires continuous breakthroughs in material and manufacturing processes, including:

• Improving large rotor forging capabilities;

• Developing higher-performance metal materials;

• Applying advanced insulation materials;

• Optimizing generator structural design.

Another critical approach to increasing generator capacity is the application of advanced cooling technologies to improve heat transfer and heat dissipation performance.

Cooling Technology: The Driving Force Behind Larger Generators

During operation, generators produce significant amounts of heat. As unit capacity increases, effectively removing heat becomes one of the most important technical challenges limiting generator development.

The history of generator development shows that every major improvement in cooling technology has enabled a new increase in generator capacity.

Advanced cooling systems help improve:

• Current density of stator and rotor windings;

• Overall generator efficiency;

• Equipment reliability;

• Maximum power output.

Development of Cooling Technologies for Overseas Steam Turbine Generators

Over the past century, leading global electrical equipment manufacturers have continuously improved generator cooling technologies. The development process has generally progressed through several stages:

Air Cooling → Hydrogen Cooling → Water-Hydrogen Cooling → Full Water Cooling

Due to differences in stator and rotor ventilation structures among manufacturers, generator capacities may vary even when using the same cooling technology.

1. Air Cooling

In the early stage of steam turbine generator development, air cooling was widely used as the primary cooling method.

Advantages:

• Simple structure;

• Easy maintenance;

• Reliable operation.

However, as generator capacity increased, the heat dissipation capability of air cooling became insufficient, limiting further increases in unit capacity.

2. Hydrogen Cooling

To improve cooling performance, hydrogen cooling technology was introduced for large generators.

Compared with air, hydrogen has:

• Higher thermal conductivity;

• Lower density;

• Lower ventilation losses.

These advantages significantly improve cooling efficiency and reduce operating losses, allowing steam turbine generators to achieve much higher capacities.

Hydrogen cooling has become one of the most important technologies for large-scale turbine generators.

3. Water-Hydrogen Hybrid Cooling

With further increases in generator capacity, hydrogen cooling alone could no longer meet heat dissipation requirements.

Water-hydrogen hybrid cooling combines:

• Water cooling for stator windings;

• Hydrogen cooling for rotor and core components.

By applying different cooling methods to different heat-generating areas, this technology greatly improves heat transfer capability and enables further increases in generator capacity.

4. Full Water Cooling

Full water cooling utilizes the excellent thermal conductivity of water to directly cool major heat-generating components inside the generator.

Advantages include:

• Higher heat transfer efficiency;

• Stronger cooling capability;

• Support for higher power density designs.

Full water cooling has become an important direction for the development of ultra-large-capacity generators.

Future Development of Large Power Generation Equipment

The evolution from air cooling to hydrogen cooling, water-hydrogen hybrid cooling, and full water cooling demonstrates that cooling technology innovation has always been a key factor driving increases in generator capacity.

In the future, with the growth of renewable energy integration, intelligent power systems, and large-scale energy projects, power generation equipment will continue to develop toward:

• Higher efficiency;

• Larger capacity;

• Lower energy losses;

• Smarter operation and control.

The integration of advanced cooling technologies, new materials, and intelligent control systems will continue to improve the performance of large-scale generators and provide more reliable and efficient power solutions for global energy development.