The core method for judging the quality of magnesium oxide insulation layers is to test their purity, insulation resistance, and physical structural integrity. High-quality magnesium oxide insulation layers should possess high purity, excellent insulation performance, and a dense and uniform filling structure.
1. Key Quality Indicators
Purity (≥99.9% is excellent)
High-purity magnesium oxide (MgO) has low impurity content, effectively reducing the risk of leakage caused by conductive impurities such as Fe₂O₃ and CaO;
High-quality products meet the standard of HG/T 6445-2025, with Cl⁻ ≤0.05% and SO₄²⁻ ≤0.03%;
The supplier can be requested to provide a component analysis certificate as verification.
Insulation Resistance (≥100 MΩ is acceptable) Cold insulation resistance measured using a 2500V megohmmeter:
≥500 MΩ: Brand new, high-quality condition;
100–500 MΩ: Normal and usable;
<10 MΩ: Unacceptable quality or severely degraded.
Hot test (test after 30 minutes of operation with power off): ≥200 MΩ.
Fill Density and Structural Uniformity
Fill density should be between 2.8–3.2 g/cm³. Too low a density can easily create voids, leading to localized overheating.
X-ray or cross-sectional inspection confirms the absence of off-center cores, voids, or delamination.
High-quality products undergo high-frequency vibration compaction + hydraulic pressing processes, resulting in a stable structure.
2. Appearance and Process Characteristics Identification
|
Characteristics |
High-Quality Performance |
Low-Quality Performance |
|
Surface Crystallization Morphology |
Magnesite-type crystals, dense and stable |
Seawater-crystal type, easily absorbs moisture |
|
Particle Size Distribution |
Mainly 100–200 mesh, uniform |
Too coarse or too fine, affects thermal conductivity |
|
Sealing Performance |
Ceramic adhesive or metal seal, IP65 or higher protection |
Ordinary silicone seal, prone to aging and cracking |
|
Wire Outlet Treatment |
Multi-layer protection: waterproof tape + heat shrink tubing + silicone coating |
Single-layer wrapping, easily affected by moisture |
If white powder (Mg(OH)₂), bulging of the casing, or corrosion of the wiring terminals is found, it indicates poor hydration resistance or poor sealing of the material.
3. Performance Testing and Verification
|
Test Item |
Acceptance Standard |
Test Significance |
|
Cold Withstand Voltage Test |
AC 2000V, no breakdown after 1 minute |
Verifies initial insulation strength |
|
Hot Insulation Resistance |
≥200 MΩ (after operation) |
Verifies stability at high temperatures |
|
Hydraulic Test |
≥200 MΩ after 48 hours at 40℃ and 95% RH |
Simulates high humidity conditions |
|
Life Test |
Insulation resistance decreases by <30% after 15000 hours of continuous operation |
Assess long-term reliability |
It is recommended to use products certified according to JB/T 2379-2016 and request the factory test report.
