1. Introduction

The copper busbar connection of stator bars and rotor coils in hydro-generators is one of the most critical processes in generator manufacturing and onsite installation. Joint quality directly affects the generator's electrical conductivity, mechanical strength, and longterm operational safety and reliability. With the continuous development of electrical welding technology, mediumfrequency induction brazing has become the most mainstream joint welding method for the end connections and collector rings of large generator units, owing to its advantages of fast heating, controllable quality, and minimal impact on the base metal.

2. Principle of MediumFrequency Induction Brazing

Mediumfrequency induction brazing utilizes the principle of electromagnetic induction: the workpiece is placed in an alternating magnetic field, causing eddy current losses within the copper busbar that generate heat. When the workpiece is heated to an appropriate temperature above the melting point of the brazing filler metal, the filler metal melts and fills the joint gap by capillary action, forming a strong metallurgical bond upon cooling. The essence of this heating method is noncontact selfheating—heat is generated directly within the workpiece rather than conducted from an external heat source.

3. Complete Equipment Composition

Taking the typical LYSD60KW mediumfrequency induction brazing equipment as an example, the complete system mainly consists of the following components:

4. Key Technical Parameters

The core technical parameters of the LYSD60KW equipment are as follows:

5. Technical Advantages

Compared with traditional brazing processes, mediumfrequency induction brazing offers significant advantages:

1. Fast Heating Speed, High Efficiency
Induction heating generates heat directly within the workpiece, eliminating preheating and heat transfer processes. A single joint can be brazed within minutes.

2. Stable and Controllable Quality
By precisely controlling heating power, temperature, and time, welding defects caused by overheating or insufficient temperature can be effectively avoided. Mediumfrequency induction brazing has become the joint welding method with the most easily controllable and assured quality.

3. Minimal Impact on Base Metal
The heating zone is concentrated with a small heataffected zone, preserving the electrical conductivity and mechanical properties of the copper busbar.

4. Energy Saving and Environmental Protection
Compared with older electrontube highfrequency power supplies, energy savings reach approximately 35%; compared with older siliconcontrolled mediumfrequency power supplies, savings reach approximately 20%, with no noise pollution.

5. Strong Adaptability
Suitable for both mass production in manufacturing plants and onsite repair work at power station pits. The handheld coaxial transformer design enables operation in confined spaces.

6. Application Scenarios

Mediumfrequency induction brazing equipment is widely used in the following scenarios:

Hydrogenerator units: Brazing of stator bar joints, butt brazing of field pole coil copper busbars.

Turbogenerator units: Brazing of stator lead joints, butt brazing of rotor winding copper plates.

Wind turbine generators: Brazing of stator and rotor copper busbars.

Large and mediumsized motors: Induction heating brazing of stator coil copper electrodes.

A typical case is the mediumfrequency welding process for stator winding bar electrical joints adopted in the installation of ALSTOM hydrogenerator units at the Three Gorges Power Station, which effectively solved the challenge of onsite welding of large bars in the pit.

7. Key Points of Process Quality Control

The brazing quality directly affects the safe operation of the generator, and the following aspects require strict control:

1. PreBrazing Cleaning
Oxides, grease, and other contaminants on the copper busbar surface must be thoroughly removed.

2. Joint Assembly
Proper and uniform joint clearance must be ensured. The brazing gap and its uniformity are key factors in guaranteeing brazing quality.

3. Temperature Control
Heating temperature should be determined based on the copper busbar material and the melting point of the brazing filler metal. Generally, 3050 °C above the melting point of the filler metal is recommended to ensure full melting and wetting of the base metal while avoiding overheating that could degrade performance. For silverbased filler metals, the brazing temperature is generally controlled between 600 °C and 800 °C.

4. Protection Measures
The equipment features water flow, pressure, and temperature detection and protection functions for the inductor. Automatic shutdown and alarm are triggered when limits are exceeded to prevent overheating damage to the handheld transformer and inductor.

5. PostBrazing Inspection
Includes visual inspection, contact resistance testing (allowable deviation ≤15% of nominal value), insulation resistance testing (≥100 MΩ at DC500 V/1000 V), and ultrasonic flaw detection, among others.

8. Conclusion

Mediumfrequency induction brazing equipment, with its high efficiency, stability, energy savings, and strong adaptability, has become the preferred process equipment for copper busbar connections in hydrogenerator coils. With the continuous advancement of IGBT transistor technology and the improvement of intelligent control levels, induction brazing equipment is evolving toward higher power density, more precise temperature control, and more comprehensive protection functions. For generator manufacturers and hydropower station operation and maintenance units, mastering mediumfrequency induction brazing technology, selecting appropriate equipment, and strictly implementing process specifications are important guarantees for ensuring the longterm safe and stable operation of generators.

The technical parameters in this article are based on the LYSD60KW mediumfrequency induction brazing equipment and are for reference only. For specific selection, please consult equipment manufacturers based on actual working conditions.

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