Why Moisture Testing Is Essential
Transformer insulation systems consist of both insulating oil and solid dielectric materials such as kraft paper and pressboard. These solid materials absorb and retain moisture more readily than oil, and they release it slowly — especially under heat and load conditions.
Excess moisture leads to:
- Reduced dielectric strength
- Accelerated thermal degradation of cellulose
- Risk of partial discharge and dielectric failure
- Increased formation of bubbles under high voltage (bubble evolution)
Test Standard
We use oven-drying (gravimetric) or Karl Fischer titration methods (depending on client requirement and accuracy level), in accordance with IEC and ASTM standards.
Test Procedure Summary
- Sample (paper or pressboard) is weighed before and after drying
- Moisture content is calculated as percentage of mass lost during drying
- Optional infrared drying or vacuum oven methods available
- Results expressed as % moisture by weight
Key Gases Measured
Insulating Liquids – Measurement of Relative Permittivity, Dissipation Factor (Tan δ) and DC Resistivity.
| Insulation Type | Acceptable Moisture (%) | Condition |
|---|---|---|
| New pressboard | < 0.5% | Dry and acceptable |
| In-service aged | 1.0% – 2.5% | Caution: Monitor |
| > 3.0% | High risk | Drying recommended |
Applications of Moisture Content Testing
- Assess dryness before transformer assembly or vacuum filling
- Evaluate condition of aged insulation for refurbishment
- Validate solid insulation quality in reclaimed units
- Support drying oven or hot air drying process verification
- Predict remaining insulation life
Our Testing Advantages
- Gravimetric oven-dry or Karl Fischer titration available
- Sample size flexibility: from 1 cm² sheets to large segments
- NABL-grade lab with temperature and humidity-controlled environment
- ERP-integrated reporting with digital moisture trend logs
- Optional insulation strength and Furan analysis available
Report Includes
- Moisture content (% by dry weight)
- Sample condition comments (e.g., brittle, discolored, aged)
- Recommendations for drying or insulation replacement
- Comparative results for multiple insulation samples (if applicable)
- Photos of sample condition (optional)
Why Choose Tru-FIL?
- Fully equipped insulation materials lab
- IEC/ASTM-compliant testing procedures
- ERP-integrated moisture analytics for trend studies
- 24/7 sample processing and expert technical consultation