Core Power Supply Requirements for High-Frequency Melting Furnaces

The power supply for a high-frequency melting furnace (often called a "Medium-Frequency Power Supply" or "Frequency Conversion Power Supply") is not just a simple power unit but a complete electrical energy conversion and control system. Its requirements can be summarized into the following key areas:

1. Power and Capacity Requirements

• Sufficient Rated Power: The power supply's rated power (kilowatts, kW) must match the furnace's capacity (kilograms per heat) and the required melting speed (kilograms per hour).

  • Rule of Thumb: Typically, a configuration of 300-500 kW per ton is needed for a reasonable melting speed. For example, a 500 kg furnace usually requires a 150 kW to 250 kW power supply.

  • Insufficient Power leads to very slow melting speeds, low production efficiency, and increased energy consumption per unit.

• Power Regulation Capability: The power supply should have a wide range and smooth power regulation functionality.

  • Start-up Phase: Lower power is needed to prevent excessive electromagnetic force impact on the cold charge and to protect the furnace lining.

  • Melting Phase: Full power operation for rapid melting.

  • Holding/Refining Phase: Reduced power is required for precise temperature control.

2. Frequency Requirements

• Frequency Selection is Critical: The output frequency (Hertz, Hz) of the power supply directly affects the "stirring effect" and thermal efficiency of melting.

  • High Frequency (Typically 1 kHz - 10 kHz):

    • Advantages: Strong skin effect, fast heating speed, especially suitable for small capacity furnaces (<500 kg) and melting high resistivity materials (e.g., gold, silver, copper, iron-chromium-aluminum). High thermal efficiency.

    • Disadvantages: Relatively weak electromagnetic stirring force.

  • Medium Frequency (Typically 150 Hz - 1 kHz):

    • Advantages: Strong electromagnetic stirring force, conducive to uniform alloy composition, temperature uniformity, and slag flotation. Suitable for larger capacity furnaces and melting steel, iron, etc.

    • Disadvantages: Slightly lower heating efficiency compared to high frequency for small charge sizes.

• Frequency Stability: The power supply should maintain stable output frequency during changes in the load (furnace charge) to ensure continuous resonant conditions and efficient energy transfer.

3. Power Quality and Efficiency Requirements

• High Power Conversion Efficiency: The intrinsic conversion efficiency (AC → DC → AC) of the power supply itself should be as high as possible (typically >95%) to reduce energy loss during operation.

• High Power Factor: Modern high-frequency power supplies commonly use capacitor compensation to ensure the system power factor remains above 0.95. This not only reduces losses from reactive power and lowers line load but also avoids penalties from the power supply company.

• Low Harmonic Pollution: Rectifier circuits using Silicon Controlled Rectifiers (SCRs) or IGBTs generate harmonics, which feed back into the grid and can affect other equipment. High-quality power supplies should be equipped with input filter devices or use technologies like 12-pulse/24-pulse rectification to meet strict grid requirements for harmonic distortion (THD), such as compliance with IEEE 519 standards.

4. Stability and Protection Requirements

• Strong Load Adaptability: During the melting process, the charge's shape, state, and electromagnetic characteristics constantly change. The power supply must automatically track and maintain the resonant state of the load circuit to ensure stable power output.

• Comprehensive Protection System: The power supply must have multiple protection functions, which are the cornerstone of safe operation. These include:

  • Overcurrent Protection: Prevents damage to power components due to short circuits or overloads.

  • Overvoltage Protection: Protects against grid fluctuations or operational overvoltages.

  • Phase Loss Protection: Prevents the power supply from operating with a missing phase.

  • Water Pressure/Temperature Protection: Interlocked with the cooling system to ensure key components like IGBTs, capacitors, and coils are not damaged by overheating.

  • Load Short-Circuit/Open-Circuit Protection: Handles extreme operating conditions.

5. Grid Connection Requirements

• Input Voltage: Depending on the power level, common ratings are 380V, 660V, 10kV, etc. The power supply should operate normally within a grid voltage fluctuation range of ±10%.

• Grid Capacity: The factory transformer capacity must be sufficient to withstand the high inrush current when the melting furnace starts and runs. Otherwise, it can cause a sharp drop in grid voltage, affecting other equipment on the same line.

Brief Comparison of Different Power Supply Types

Practical Checklist for Selecting a Power Supply

When selecting or evaluating a power supply for your melting furnace, consider the following questions:

• Define Production Needs:

  • What metal(s) will be melted primarily? What is their resistivity? (Determines frequency orientation)

  • What is the maximum capacity per heat? What is the target melting cycle? (Determines power size)

• Evaluate Power Supply Performance:

  • Does the power supply's rated power and output frequency range meet my needs?

  • What are the power supply's conversion efficiency and power factor? (Directly impacts electricity costs)

  • Is necessary filtering equipment included to meet grid harmonic standards?

• Check Protection and Compatibility:

  • Are the protection functions comprehensive (overcurrent, overvoltage, water temperature, etc.)?

  • Is the power supply compatible with my existing furnace body (coil, capacitors)?

  • Is the control interface user-friendly? Can it be easily integrated into my production system?

• Verify External Conditions:

  • Can my factory's grid voltage and transformer capacity support the operation of this power supply?

  • Can the cooling water system's quality and flow rate meet the power supply's heat dissipation requirements?

Conclusion

In summary, a high-frequency melting furnace requires its power supply to have appropriate power and frequency, extremely high power conversion efficiency, stable output performance, and comprehensive, reliable protection functions. Choosing a power supply that perfectly matches your production process is key to achieving efficient, energy-saving, safe, and economical operation. In modern applications, the IGBT Medium Frequency Power Supply has become the preferred solution for most scenarios due to its excellent overall performance.