Mining Dry-Type Transformer

I. Working Principle
The mining dry-type transformer operates on the fundamental law of electromagnetic induction. Alternating current supplied to the primary winding generates an alternating magnetic field, which is coupled through the core to induce required voltages in the secondary winding, thereby achieving efficient voltage transformation. Unlike standard industrial dry-type transformers, it adopts an epoxy resin vacuum-cast, fully sealed structure. The high and low-voltage windings are hermetically encapsulated in high-performance resin, eliminating flammable insulating oil entirely. The unit relies on natural air convection (AN) or forced-air cooling (AF) for thermal dissipation, making it ideally suited for the hazardous, explosion-proof, and moisture-prone environments of underground mining.

II. Key Performance Characteristics

Major Advantages:

Inherent Safety & Flame Retardancy: Completely free of transformer oil, eliminating all risks of oil leaks, fires, or explosions. The resin-cast windings feature outstanding arc resistance and self-extinguishing properties, preventing the ignition of underground methane (firedamp) and coal dust, and fully complying with stringent underground explosion-proof safety standards.

Superior Environmental Resilience: The fully sealed encapsulation offers exceptional resistance against dust, moisture, condensation, and dripping water, reliably withstanding harsh underground conditions characterized by high humidity, airborne particulates, and corrosive gases.

Simplified Maintenance: Eliminates tedious routine procedures such as insulating oil sampling, laboratory testing, oil purification, and replacement, significantly reducing operational expenditure. It is typically equipped with an intelligent temperature control system (PTC/Pt100) for real-time winding thermal monitoring, over-temperature alarming, and trip protection.

High Flexibility & Compactness: Features rugged, vibration-resistant construction that allows compact spatial integration, making it the perfect match for underground mobile substation skids.

Inherent Limitations:

Higher Cost & Thermal Constraints: Initial procurement costs are higher than equivalent oil-immersed transformers. Due to thermal conduction limits imposed by the solid resin encapsulation, short-term overload capacity is slightly lower than that of oil-filled counterparts.

Difficult Field Repair: The resin encapsulation is a monolithic solid structure, rendering field insulation repairs virtually impossible. In the event of severe winding internal faults, complete replacement or factory overhaul is usually required.

Weight & Logistical Challenges: Due to robust enclosures and dense casting construction, high-capacity models are relatively heavy, posing logistical challenges during underground transport and maneuvering in restricted spaces.

III. Application Scenarios
Primarily deployed in underground coal mines, metal, and non-metal subterranean mining power distribution networks, frequently serving as the core transformer unit for explosion-proof mobile substations:

Mining Machinery Power Supply: Delivering low-voltage power to underground continuous miners, roadheaders, heavy-duty armored face conveyors (AFCs), belt conveyors, and hydraulic pump stations.

Auxiliary & Safety Infrastructure: Supplying power to underground working faces, tunnel lighting, environmental monitoring systems, and underground communication networks.

Critical Infrastructure Feeding: Powering essential underground installations such as main drainage pump rooms and auxiliary ventilation fans.

Surface Industrial Facilities: Widely utilized in open-pit mining operations, coal preparation plants, and mineral processing facilities characterized by heavy dust accumulation or stringent fire safety requirements.

Summary
With intrinsic safety, fire resistance, and explosion-proof capability as its core strengths, the mining dry-type transformer stands as vital backbone equipment ensuring safe and continuous power supply in underground mines. By leveraging a fully sealed resin-cast dry structure to eradicate oil-related fire and explosion hazards, it guarantees secure power delivery for gassy underground mobile substations and heavy extraction machinery.

Specification for 10000V Mining Dry-type Transformer

Specification for 6000V Mining Dry-type Transformer

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.

Youth Transformer Co.,Ltd.