The power supply system plays a crucial role in the vacuum induction melting furnace (VIM) by ensuring stable, efficient, and safe melting processes. The system includes the following key modules:
- Rectification and inversion module
- Capacitor station
- Output isolation transformer
- Stirring system (for homogenizing and degassing the molten steel)
For a 6-ton VIM, the power supply system’s output power range is between 1600kW and 2000kW, with a frequency range of 200Hz to 300Hz. It uses a single-phase output solid-state medium-frequency power supply. The system is powered by a 2200kVA three-phase 50Hz input transformer, providing efficient power support to the furnace.
1. Power Characteristics and Stability of the Power Supply System
The melting power supply runs at full power during the melting phase (without stirring), ensuring the power factor is greater than 0.9. This is essential for improving system efficiency and minimizing energy waste. A stable and reliable power supply system is designed to smoothly start up under various load conditions (idle, light load, and heavy load), maintaining stable operation throughout.
The design also emphasizes minimizing the impact on the power grid. Harmonic components are reduced to limit pollution to the grid. The power supply system features an automatic frequency tracking function, ensuring that maximum power output is maintained throughout the melting process. The melting speed can be adjusted through power control.
Additionally, the system is equipped with complete protection circuits and safety interlock alarms. These features enable quick response to potential faults, ensuring that the equipment remains safe and operational. The high reliability of the design guarantees stable performance even during long, continuous operations.
2. Stirring Function Requirements and Design
To improve the internal quality of alloy ingots and ensure proper degassing and alloy homogenization, large vacuum induction furnaces typically require a stirring function. Electromagnetic stirring is the most commonly used technology, which generates rotational motion in the molten steel through an electromagnetic field. This promotes the complete mixing of the molten steel and the removal of gas.
There are two main types of electromagnetic stirring technology:
1) Three-Phase Power Frequency Stirring
Three-phase power frequency stirring is a mature and widely applied electromagnetic stirring technology, particularly suitable for large furnaces. Its main characteristics include:
- Good capacity adaptability: Three-phase power frequency stirring is suitable for furnaces of various sizes, especially large ones. It effectively enhances the uniformity of the molten steel.
- High maturity: The technology has been widely used and provides stable performance and reliable operation.
In three-phase power frequency stirring, the induction coil usually consists of three groups of windings, forming a balanced magnetic field. This design ensures that the molten steel is adequately stirred during the melting process, improving melting quality.
2) Single-Phase Stirring (UDS)
Single-phase stirring (UDS) technology is a new method invented in the United States, typically used in smaller furnaces. Its characteristics include:
- Lower manufacturing cost: Compared to three-phase power frequency stirring, single-phase stirring is more cost-effective, making it suitable for smaller furnaces that need to reduce costs.
- Weaker stirring effect: While single-phase stirring offers some stirring capability, its performance is not as strong as three-phase power frequency stirring, especially in larger furnaces.
In single-phase stirring, the induction coil typically consists of two or three groups, with two groups being more common. (e.g., Inductotherm uses two groups, while AJAX may use two or three). Despite its slightly weaker stirring performance, single-phase stirring still provides effective mixing for smaller furnaces and offers cost advantages.
3. Comprehensive Characteristics of the Power Supply System
Vacuum induction furnaces above 6 tons typically use three-phase power frequency stirring, which provides stronger stirring force, particularly suitable for large furnace operations. The power supply system design not only ensures furnace stability during high-power operation. But also effectively reduces the impact of higher-order harmonics, ensuring the equipment remains friendly to the power grid. Additionally, the system’s frequency auto-tracking function ensures that the power output remains optimal during the melting process, improving efficiency and shortening the melting cycle.
Overall, the design of the power supply system ensures the efficient and safe operation of the equipment by selecting the right power control, stirring mode, and protection mechanisms. Whether under light or heavy loads, or in different furnace configurations, the power supply system provides stable electrical support, advancing the vacuum induction melting furnace towards higher efficiency and reliability.
