I. Project Background and Equipment Specifications

This case study involves a medium frequency induction melting furnace, model WDL-KGPS-500, with a rated capacity of 0.5 tons and a maximum capacity of 0.6 tons, designed for aluminum melting applications. The equipment employs medium frequency induction heating and is equipped with a hydraulic tilting system for molten aluminum discharge.

The most notable configuration feature of this equipment is its grid compatibility scheme: the power supply side is fed at 440V/3P/60Hz, while the medium frequency power supply input voltage is specified at 380V. This means the equipment is intended for 60Hz grid regions (such as South Korea, parts of Central and South America, and the Middle East), requiring a transformer or voltage adaptation unit either inside or external to the power supply cabinet to step down the 440V grid voltage to 380V before feeding the medium frequency power supply. This dual adaptation of both voltage and frequency is a parameter that must be confirmed upfront during the electrical design phase for export projects.

II. KGPS Medium Frequency Power Supply System

The power supply system adopts the KGPS thyristor-based medium frequency power supply, with a rated power of 400 kW, a medium frequency output voltage of 2400 volts, and an output frequency of 1000 Hz. The power factor exceeds 0.9, and the startup success rate is 100%. The rectifier section is a three-phase full-controlled bridge with a three-phase six-pulse rectifier structure and a parallel-connected inverter.

The control circuit employs an eighth-generation digital circuit board architecture, featuring wide frequency range adaptability, constant power control, swept-frequency zero-pressure soft start, and dual closed-loop voltage-current feedback. The swept-frequency zero-pressure startup means the system automatically scans frequencies during startup, establishing medium frequency oscillation upon finding the load resonant point – avoiding the sensitivity to load parameter variations inherent in separate-excitation startup methods.

The protection system encompasses overcurrent, overvoltage, undercurrent, undervoltage, water loss, and phase-loss conditions. When any protection parameter exceeds the set threshold, the system automatically blocks pulse output and disconnects the main circuit power. The power supply cabinet panel includes full voltage, current, and power readings along with operating status indicators.

The capacitor cabinet provides medium frequency parallel compensation, reducing reactive power transmission losses on the distribution lines. The capacitor bank capacity is matched to the resonant frequency of the induction coil, ensuring operation near the resonant point under rated conditions.

III. Induction Coil Design and Magnetic Yoke Shielding

The induction coil is the core energy conversion component, constructed from T2/TU1 copper with a wall thickness of 4 mm. When energized, the coil generates a 1000 Hz alternating magnetic field that induces eddy currents in the metal charge within the furnace hearth, generating heat. The coil design is based on electromagnetic field principles and verified through dedicated computer software, with the deviation between actual operating power and design power controlled within 5%.

Turn-to-turn insulation is processed using advanced insulation techniques, with dedicated clamping technology reducing axial vibration of the coil. The coil inner wall is sprayed with imported high-temperature-resistant insulating materials, and a furnace lining leakage alarm system is installed – when molten aluminum seeps into the coil layer, the system detects it early and signals the condition, preventing furnace breakout incidents. A refractory coating of 10 to 15 mm thickness is applied to the inner surface of the coil, serving both to facilitate furnace lining construction and to prevent thermal deformation of the lining.

The magnetic yokes are of crescent profile construction, laminated from cold-rolled silicon steel sheets and clamped with stainless steel splints. The contact surface between the yoke and the coil outer surface is curved, providing face contact rather than line contact, achieving better clamping efficiency and reduced magnetic flux leakage. The silicon steel sheets are reinforced with dedicated splints rather than through-bolts, maximizing the effective magnetic area and reducing localized heating. The magnetic yokes simultaneously shield magnetic flux leakage, prevent furnace body heating, and support and secure the induction coil.

IV. Hydraulic Tilting System

Furnace tilting is driven by a hydraulic system with two cylinders arranged on both sides of the furnace body for lifting, with furnace return accomplished by gravity. The hydraulic station is equipped with dual motors and dual pumps – one in service and one on standby, with automatic switching capability. The fuel tank is fully enclosed and welded to prevent hydraulic oil leakage.

The tilting angle range is 0 to 95 degrees, with smooth operation without shock or creeping, adjustable speed, and the ability to hold at any position. Tilt operation is controlled via manual valves, suitable for casting processes requiring precise control of molten aluminum pouring volume.

V. Crucible Mold and Lining Formation

A configuration detail of this equipment is that it supplies a crucible mold rather than a finished graphite crucible. The crucible mold is formed from 3 mm iron plate and is used to control the shape and volume positioning of the refractory lining during formation. The user must select the lining material and ramming/sintering method according to the specific metal being melted and the casting process – a difference at the user operation level compared to solutions that directly supply finished graphite crucibles. The positioning function of the crucible mold ensures dimensional consistency of the lining cavity, thereby maintaining the coupling distance between the furnace hearth and the induction coil stable within the design range.

VI. Water Cooling System and Cooling Cables

The water-cooled cables are constructed from TU1 multi-strand oxygen-free copper wire, sheathed in high-strength fire-resistant rubber tubing, with cold-formed connectors ensuring contact resistance and tensile strength. The power supply side requires a cooling water flow rate of no less than 8 m³/h, while the furnace body side requires no less than 12 m³/h. The outlet water temperature on the power supply side must not exceed 35°C, and on the furnace body side must not exceed 45°C, with inlet water pressure maintained between 0.15 and 0.35 MPa.

The water cooling system employs a fully enclosed circulating cooling method using soft water as the circulating medium. The core advantage of soft water circulation lies in avoiding overheating damage to the power supply, thyristors, capacitors, IGBT modules, and induction coil caused by scale deposition; additionally, soft water contains no ionic conductive components, so cooling components will not be damaged by electrolysis. The system requires no water pool or cooling tower, occupies minimal floor space, and has low makeup water consumption.

The cooling system consists of three parts: main machine, water tank, and control box. The main machine includes the housing, copper cooler, exhaust system, spray system, water separator, collecting annulus, and spray pump. The water tank includes the main pump (one in service, one standby), stainless steel water tank, electrical cabinet, temperature control system, and pressure control system. The control box enables remote operation of the water cooling system, displaying water temperature and allowing setup of delayed operation after work hours.