Medium Frequency Furnace Power Supply and Phase Balancing Solutions

A medium frequency induction furnace relies on a low-frequency power supply unit, which connects a single-phase induction heating coil at the output to a three-phase power grid at the input. For safe and stable operation, it is critical to maintain a balanced three-phase current. If the imbalance exceeds the permissible range, additional phase balancing equipment—such as reactors and capacitors—must be installed to stabilize the furnace load. This ensures reliable performance and protects the power supply network.

Power Supply Circuit and Balancing Equipment

The basic circuit design typically uses reactors and capacitors to balance the single-phase load, allowing the system to operate as a nearly balanced three-phase circuit. Depending on site requirements, these components may have fixed or variable capacity. However, the reactive and capacitive currents introduced must be carefully matched with the network’s electrical characteristics. If not properly configured, series resonance can occur during the melting cycle, which may damage equipment or reduce efficiency.

To regulate input power, most furnaces adjust the secondary voltage of the transformer by selecting the appropriate tap setting. This method enables precise furnace voltage control during operation.

Switching and Power Control

Traditionally, many systems use a load-tap changer on the transformer. However, when this switch operates, high-frequency switching currents are generated. These transients can cause voltage drops on the power supply line and place additional stress on electrical insulation, increasing the risk of equipment failure. Frequent opening and closing of circuit breakers and contactors also raise maintenance costs and shorten component lifespan.

Modern designs increasingly adopt saturated reactor systems for smoother power control. Yet, these single-phase systems should only be used if the network can tolerate unbalanced loads without phase balancing equipment. Otherwise, the introduction of extra harmonic currents requires filtering, which adds more reactors and capacitors. This not only complicates the system but also increases electrical losses and reduces overall furnace efficiency. For this reason, saturated reactor control is not recommended where three-phase balancing devices are already necessary.

Start-Up and Smooth Operation

One of the challenges of medium frequency furnaces is the impulse current generated during start-up. To minimize this, many systems use a balanced starting circuit on the transformer’s secondary winding. Typically, the main circuit breaker energizes the transformer once per work cycle (or even once per lining life), while switching contactors connect or disconnect the secondary side.

A practical solution is to start with a series resistor in line with the furnace coil. This resistor reduces inrush current and voltage drop at the moment of energization, then is short-circuited within seconds as the furnace reaches normal operation. In weaker power networks (with low short-circuit capacity), two-stage or three-stage resistor switching can be used for even smoother performance.

Power Factor Compensation and Reliability

In high-power furnace installations, power factor correction capacitors may also be switched using staged resistor systems to avoid sudden surges. Well-engineered power supply cabinets combine automatic phase balancing with soft-start switching technology, ensuring stable performance even under moderate grid fluctuations.

When designed and installed properly, these systems deliver:

• Stable power distribution with reduced voltage drop
• Lower harmonic distortion and fewer electrical failures
• Extended equipment life for transformers, contactors, and capacitors
• Higher operational efficiency, reducing downtime and operating costs

Why This Matters for Global Buyers

For steel foundries, copper smelting, and other industrial applications, a reliable medium frequency induction furnace power supply is critical for production efficiency and cost savings. By choosing a system with advanced phase balancing, harmonic filtering, and soft-start technology, buyers can ensure:

• Greater energy efficiency
• Reduced maintenance expenses
• Improved furnace safety and reliability

At Luoyang Judian, we provide customized medium frequency induction melting furnaces with advanced power supply systems designed for global industrial users. Our solutions are optimized for international standards, making them suitable for foundries and metallurgical plants worldwide.