Dry-Type Transformer Maintenance and Common Fault Handling
1. Features of Dry-Type Transformers
Dry-type transformers are cooled by natural air convection, with windings cast in epoxy resin (e.g. the SCB series). Compared with oil-immersed transformers they are flame-retardant and explosion-proof, oil-free, easy to install and low-maintenance, and are widely used in workshop distribution, data centers, commercial buildings and other locations with strict fire-protection requirements. Common capacities range from 30 kVA to 2,500 kVA; for example, an SGCLB-75/0.48 is a special 75 kVA, 0.48 kV-class dry-type transformer.
2. Routine Inspection Points
- Temperature monitoring: the temperature controller displays winding temperature — normally below 110℃ (Class F insulation); verify the 130℃ alarm and 150℃ trip settings. Periodically use an infrared thermometer to check that temperature distribution across windings and busbar joints is even
- Sound diagnosis: a normal unit produces an even hum; crackling discharge sounds usually indicate surface tracking caused by dust and moisture
- Visual inspection: check winding surfaces for cracks or discharge burn marks, and insulators for dust and flashover traces
- Cooling fans: automatic temperature-controlled fans should start around 100℃; test the fans and temperature interlock periodically
- Tightness and grounding: HV/LV busbar bolts, neutral grounding and enclosure grounding must be checked at least once a year
3. Common Fault Handling
Abnormal winding temperature rise: usually caused by overload or blocked air ducts — verify load rate and clean dust from cooling ducts. Dropping insulation resistance: units stopped in damp environments absorb moisture; before energizing, measure with a 2,500 V megohmmeter and dry the transformer if resistance is below code. Trip/outage: check the controller records to distinguish overtemperature trips from external short-circuit impacts; after clearing the fault, manually reset the temperature controller before re-energizing.
4. Recommended Maintenance Intervals
Monthly visual inspection and temperature recording; quarterly de-energized cleaning of winding surface dust (blow with dry compressed air); annual insulation-resistance and grounding-resistance testing plus a full fastener check; shorten intervals in harsh environments (dusty or corrosive gas).