The insulation grade of mining transformers is a critical technical parameter that directly affects their safety, reliability, and service life in harsh underground environments (high humidity, dust, potential chemical corrosion, and strict explosionproof requirements). Below is a comprehensive, parameterized guide to insulation grades for mining transformers, covering core definitions, common grades, application scenarios, and key selection criteria—tailored for engineering design, material selection, and quality inspection.

　　1. Basic Definition of Insulation Grade

　　The insulation grade of a transformer is classified by the maximum allowable temperature rise of the insulation material (under rated load and normal operating conditions). It determines the transformer’s thermal endurance, overload capacity, and service life (the service life of insulation materials is halved for every 8–10°C increase beyond the rated temperature, following the Arrhenius law).

　　Key indicators for mining transformers:

　　Rated insulation temperature (℃): Maximum temperature the insulation system can withstand longterm.

　　Temperature rise limit (K): Allowable temperature increase of the winding/iron core relative to the ambient temperature (ambient temperature for mining transformers is typically specified as 40℃, per IEC 60076 or GB/T 1094 standards).

　　2. Common Insulation Grades for Mining Transformers

　　Mining transformers (especially flameproof or intrinsically safe types) prioritize insulation materials with high thermal stability, moisture resistance, and flame retardancy. The following are the most widely used grades, with quantified parameters:

　　3. Key Selection Criteria for Mining Scenarios

　　Mining transformers must comply with industryspecific standards (e.g., IEC 600790 for explosion protection, GB 8905 for mining electrical equipment) and consider the following factors:

　　(1)Environmental Conditions

　　Humidity: Underground mines have relative humidity often >90%. Prioritize insulation materials with moisture resistance (e.g., epoxy resinimpregnated Class B/F, silicone rubber Class H) to avoid insulation breakdown.

　　Temperature: Ambient temperature in deep mines may exceed 40℃. Select grades with temperature rise margins (e.g., Class F/H) to prevent overheating.

　　Corrosion: Mines with sulfur dioxide (SO₂) or hydrogen sulfide (H₂S) require chemicalresistant insulation (e.g., Class H silicone resin, Class C PTFE).

　　(2)ExplosionProof Requirements

　　Flameproof transformers (Ex d I Mb): Insulation materials must be flameretardant (meet GB/T 1408.12013) to prevent ignition of coal dust/gas. Class B/F are preferred for oilimmersed types (mineral oil + epoxyimpregnated insulation), while Class F/H are used for drytype (epoxy casting).

　　Intrinsically safe transformers (Ex ia I Ma): Insulation must have low leakage current and high dielectric strength (Class E/B for lowpower, Class F for mediumpower).

　　(3)Load Characteristics

　　Continuous load: For 24/7 operation (e.g., main power distribution transformers), select Class B/F with longterm thermal stability.

　　Intermittent/overload: For transformers powering mining machinery (e.g., conveyors, drills), choose Class F/H to withstand shortterm temperature spikes.

　　(4)Standards Compliance

　　Mandatory standards: GB/T 1094.11 (oilimmersed mining transformers), GB/T 10228 (drytype mining transformers), IEC 6007611 (international standard for mining transformers).

　　Insulation resistance test: At 20℃, the insulation resistance of the winding to ground should be ≥100 MΩ (for 10kV transformers), and the dielectric strength test should pass 35kV/1min (AC) without breakdown.

　　4. Typical Product Examples & Parameters

　5. Maintenance & Inspection Focus

　　To ensure insulation performance, regular tests are required:

　　Insulation resistance test: Use a 2500V megohmmeter; for Class B/F transformers, the resistance should not be less than 1 MΩ/kV (at operating temperature).

　　Dielectric loss tangent (tanδ) test: tanδ ≤ 0.05 (at 10kV, 70℃) for oilimmersed transformers, indicating no insulation aging.

　　Temperature monitoring: Use embedded thermocouples to track winding temperature; avoid exceeding the rated insulation temperature (e.g., ≤130℃ for Class B, ≤155℃ for Class F).

　　Summary

　　The insulation grade of mining transformers is primarily determined by environmental conditions, explosionproof requirements, and load characteristics. Class B and F are the most commonly used grades (balancing cost and performance), while Class H/C are reserved for extreme scenarios. When selecting, prioritize compliance with miningspecific standards, quantify temperature rise and insulation resistance parameters, and match the grade to the actual operating environment to ensure longterm safe operation.

　　For specific transformer models or project requirements, provide rated power, voltage level, and environmental parameters for a more targeted insulation grade recommendation.