Mine flameproof dry-type transformer

Mine flameproof dry-type transformer
Transformer used in explosion-hazardous places in mines
Mine flameproof dry-type transformer is a power equipment designed for explosion-hazardous environments in mines. Its casing joint surface adopts a flameproof structure and can withstand an internal pressure of 0.8 MPa, complying with explosion-proof standards such as GB3836. It is widely used in underground environments containing methane and coal dust, and can provide power for mining equipment, mobile substations, etc., and has both underground and underground versatility to reduce infrastructure investment [1].
The transformer adopts solid insulation processes such as epoxy resin casting and composite insulation, and its heat resistance grade is mostly H grade. The iron core adopts a low-height design of cold-rolled silicon steel sheets, which is suitable for tunnel transportation conditions and has a capacity range of 4kVA to 6300kVA [3]. The input voltage supports 380V/660V to 10kV, and the output voltage covers 127V-3450V, meeting the needs of underground equipment [2]. Models above 100kVA often combine with explosion-proof switchgear to form a mobile substation. The box structure incorporates corrugated steel plates to enhance heat dissipation and mechanical strength. Some models are equipped with temperature relays for over-temperature warning and have passed coal mine safety and explosion-proof certification.
Applications
1. In emergencies requiring immediate emergency power supply due to natural disasters or equipment failures, if the system lacks spare capacity, this substation can fully or partially replace a conventional substation to quickly provide power.
2. In mining area power supply, mobile substations can meet the high-capacity, high-voltage power requirements of heavy mechanized coal mining units and can be moved with the mining face, effectively addressing issues such as excessive voltage drop or insufficient short-circuit protection sensitivity.
3. When power demand is rapidly growing, the power supply distance is relatively long, exceeding pre-planned power construction, and the construction of a permanent substation is difficult, these substations can be used as temporary substations to alleviate power supply constraints, such as in coal mine extension projects.
4. When construction of a permanent substation in a certain area is suspended due to funding shortages or other reasons, these substations can be used as temporary substations. 5. Mobile mine substations are not only used for underground coal mine power supply, but can also be expanded to surface power supply systems. They are universally applicable both underground and underground, further improving equipment utilization. They also reduce investment in land acquisition, civil engineering, and substation equipment installation, thereby lowering operating costs.

Physical Structure

It consists of the main body of the mine transformer, a high-voltage head at the high-voltage incoming line (used to control the high-voltage incoming line and equipped with a protection circuit), and a low-voltage head at the low-voltage outgoing line (used to control the low-voltage incoming line and equipped with a protection circuit).

Insulation
Solid insulation. The solid insulation of epoxy-resin cast dry-type transformers consists of a casting resin combined with a resin-impregnated material (such as glass fiber or film). Solid insulation is primarily used for winding insulation (such as turn insulation), inter-segment insulation in segmented layered windings, and insulation around windings and leads. The most serious problem with solid insulation is the development of cavities in the casting or cracking during operation, which can cause partial discharge, leading to long-term insulation degradation and breakdown.

Composite insulation (air + solid) Composite insulation primarily includes the insulation between the high- and low-voltage windings, the insulation between the high-voltage winding and the core (to ground), and the insulation between the high-voltage winding and the voltage winding (interphase insulation). This insulation is essentially equivalent to the main insulation of an oil-immersed transformer. The dielectric constant ratio of air to epoxy resin is approximately 1:3.5, so the field strength acting in the air gap is higher than that of epoxy resin. However, the dielectric strength of epoxy resin is significantly higher than that of air, so the overall insulation strength depends on the air gap.

Creeping insulation: This insulation is between the terminals on the cast surface of the insulation paper, and between the cast winding and the surface of the supporting insulation. Creepage insulation is primarily affected by creeping discharge, which is significantly affected by surface contamination and moisture absorption.

Heat-resistant grade
Mining dry-type transformers typically have capacities of 4 kVA and 2.5 kVA, and are designed to power equipment such as electric drills, lighting, and signaling. Cables are routed through lead-out sleeves. The primary voltage is either 380 V or 660 V; the secondary voltage is typically 133 V. Flameproof transformers with a capacity of 100 kVA or above are often combined with flameproof switchgear to form flameproof mobile substations. Output voltages are available in 400 V, 690 V, and 1200 V to meet the needs of mine electrical equipment. To accommodate tunnel transportation, the transformer structure must be low. This allows for a larger iron column diameter, typically made of cold-rolled silicon steel sheets. Transformers with a capacity of 100 kVA or above typically utilize Class H insulation.