Electric Furnace Transformer

I. Working Principle
The electric furnace transformer is a specialized power transformer engineered specifically to supply power to various industrial electric furnaces. Operating on the fundamental law of electromagnetic induction, it steps down high grid voltage and provides flexible voltage regulation tailored to the electrical characteristics of furnace heating elements, electric arcs, or molten charges. Since resistance furnaces, salt-bath furnaces, and similar thermal equipment typically feature extremely low impedance, with heating element resistance fluctuating dramatically during heating and melting cycles, they cannot be directly connected to standard utility grid voltages. The furnace transformer utilizes multi-stage voltage regulation (via tap changers or booster configurations) to drastically reduce input voltage and output massive secondary currents, delivering a stable, highly adaptable low-voltage, high-current power supply required for optimal thermal performance.

II. Key Performance Characteristics

Tailored Load & Thermal Management: A defining characteristic of electric furnace transformers is their capacity- and duty-dependent cooling architecture:

Dry-Type Natural Air Cooling: Low-capacity, low-voltage transformers for compact resistance or salt-bath furnaces typically feature enclosed dry-type structures relying on natural air convection (AN), offering structural simplicity and ease of maintenance.

Oil-Immersed Self/Air Cooling: Medium-capacity units (ranging from hundreds to thousands of kVA) generally adopt oil-immersed self-cooled (ONAN) or forced-air cooled (ONAF) designs, providing high thermal inertia and stable performance for continuous industrial duties.

Forced Oil Circulation Water Cooling: Large-capacity industrial furnace transformers utilize forced oil circulation with water cooling (OFWF), achieving high-efficiency thermal exchange through external heat exchangers to sustain massive loads during prolonged, high-intensity melting operations.

Superior Electrical Performance:

Low-Voltage, High-Current Output: The secondary side delivers exceptionally low rated voltages (ranging from tens to hundreds of volts) paired with massive rated currents reaching thousands or tens of thousands of amperes.

Wide Regulation Range: Equipped with extensive multi-stage voltage adjustment capabilities (via off-circuit or on-load tap changers - OLTC) to compensate for dynamic impedance shifts during the charge melting phase.

High Short-Circuit & Overload Resilience: Engineered with superior mechanical winding strength and specialized impedance to withstand frequent electrode short circuits and violent load surges inherent to furnace operations.

III. Typical Application Scenarios
Widely deployed across metallurgical, mechanical machining, advanced materials, and industrial heating sectors:

Heat Treatment & Sintering: Powers industrial resistance furnaces, pit furnaces, and box-type furnaces for metal component annealing, quenching, and tempering; heavily utilized for metal powder sintering in powder metallurgy.

Non-Ferrous Metal Melting: Matches salt-bath furnaces and supports melting and holding operations for copper, aluminum, zinc, and their respective alloys.

Specialized Industrial Heating: Supplies dedicated power for chemical electric heating reaction vessels, specialized ceramic sintering, and high-temperature graphitization processing.

Summary
With low-voltage high-current output, flexible multi-stage regulation, and rugged duty-specific cooling as its core strengths, the electric furnace transformer serves as the critical energy-conversion backbone ensuring stable heating, efficient melting, and precise thermal processing in industrial furnace systems.

Quality Assurance & Core Process：

1. High-Permeability Grain-Oriented Electrical Steel

We utilize Hi-B high-permeability grain-oriented (HPGO) electrical steel—the same grade specified by TBEA and CHINT—as the transformer core material, with standard nominal thicknesses of 0.23 mm and 0.27 mm. Core laminations are manufactured using high-precision cutting equipment to guarantee a burr height of ≤0.02 mm. The assembly incorporates a precision step-lap lamination structure, maintaining optimal clamping pressure without imparting excessive mechanical stress to the electrical steel, combining high-B steel characteristics with an optimized magnetic flux density.

2. High-Conductivity Winding Conductors & Core-Coil Assembly

High-conductivity electrolytic copper or aluminum conductors are selected based on transformer capacity, voltage class, and loss requirements. Incoming materials undergo stringent quality inspections for dimensions, electrical resistance, surface quality, and traceability. During the winding process, conductor tension, winding height, layer insulation, and conductor positioning are precisely controlled to ensure resistance consistency and mechanical stability, thereby minimizing load losses and temperature rise during operation.

During core-coil active part assembly, coil height, axial clamping force, radial support, and spacer block positioning are precisely controlled. Proper mechanical clamping prevents coil displacement during transport, normal operation, and short-circuit conditions. Meanwhile, clamping forces are strictly regulated to avoid excessive stress on conductors and insulation materials. Our mechanical design accounts for both radial and axial electromagnetic forces, safeguarding short-circuit withstand capability and long-term dimensional stability.

3. Advanced Insulation System (Oil-Immersed & Dry-Type)

For oil-immersed transformers, we utilize high-grade insulation materials, including Kraft paper, thermally upgraded paper, pressboard, and transformer-grade laminated board. For dry-type transformers, we employ DMD, NMN, Nomex, fiberglass, and epoxy resin systems. Insulation thickness, overlap width, oil duct dimensions, electrical clearances, and mechanical positioning are strictly regulated. All insulation materials are stored under climate-controlled conditions to minimize moisture absorption and contamination, ensuring stable dielectric strength and long-term insulation reliability.

4. Controlled Vacuum Drying

We apply a controlled drying curve regulated by temperature, vacuum level, and duration parameters, rather than relying on fixed cycle times. The process comprises controlled pre-heating, evacuation, primary drying, and final soak phases, with continuous temperature and vacuum monitoring and logging. End-point determination is based on validated process criteria and moisture limits. This process minimizes residual moisture in cellulose insulation, maximizing dielectric strength, retarding insulation aging, and extending overall service life.

5. Vacuum Epoxy Resin Casting

For cast-resin dry-type transformers, we utilize controlled vacuum casting technology. Resin-to-hardener ratio, material temperature, vacuum level, mixing time, pouring conditions, and curing temperatures are strictly regulated. Vacuum degassing minimizes micro-voids prior to pouring, while controlled curing ensures stable mechanical and thermal properties. Finished coils undergo thorough visual and electrical inspections, including routine partial discharge (PD) testing. This process eliminates internal voids, ensuring reliable insulation performance throughout the transformer's service life.

6. Clean Assembly & Torque Control

Final assembly takes place in a controlled environment to minimize contamination from dust, metallic particles, and foreign objects. Critical components are inspected for cleanliness, dimensional accuracy, and insulation condition. Electrical clearances, lead routing, grounding connections, and mechanical supports are rigorously controlled throughout assembly. Critical bolted joints are tightened to specified torque values using calibrated equipment and fully logged. Prior to sealing the tank or enclosure, a thorough internal inspection ensures no tools, loose parts, or foreign material remain.

7. 100% Factory Routine Testing

Every transformer undergoes 100% routine testing prior to dispatch, complying with applicable IEC standards, approved technical specifications, and customer requirements. Standard test routines include winding DC resistance, voltage ratio, vector group verification, no-load loss and current, load loss and short-circuit impedance, applied voltage withstand, and induced overvoltage withstand tests. Special tests—such as partial discharge (PD), dissipation factor (tan δ), or sweep frequency response analysis (SFRA)—are conducted upon request. Each unit is assigned a unique serial number linked to its material records, manufacturing data, and final test reports, ensuring end-to-end traceability.