1. Heading and Context
During long-term operation, dry-type transformers often face risks of localized overheating and insulation breakdown caused by dust accumulation, moisture, or loose fasteners. How can scientific maintenance methods eliminate these potential failures in their infancy? Based on power industry standards, this article systematically outlines the operational specifications for dry-type transformers, ranging from daily inspections to in-depth maintenance.
- Equipment Scope: Applicable to SCB10/11/13/14/18 and other series of three-phase cast resin dry-type transformers.
- Operating Environment: Primarily targeted at distribution rooms, IDC data centers, and load centers in high-rise buildings.
- Maintenance Cycle: Daily/Weekly inspections and Preventive Testing (every 1–3 years).
2. Fault Description
Maintenance personnel must possess keen observational skills to capture "distress signals" sent by the equipment through subtle changes.
- Protection Actions: High-temperature alarms from the controller (typically set at 130∘C for alarm and 150∘C for trip) or trip reports.
- Abnormal Sounds: Heavy "humming" (loose core or overload) or irregular "cracking" discharge sounds (surface tracking/creeping).
- Physical Anomalies: Severe dust accumulation on insulator surfaces, carbonized paths (electrical trees) on epoxy resin surfaces, or fan failure.
- Temperature Deviations: Significant imbalance in the temperatures of the three-phase windings or a sudden spike in one phase.
3. Testing and Data Analysis
Using data to speak is the only criterion for measuring the health of a transformer.
- Insulation Resistance Test:
- Requirement: Use a 2500V megohmmeter to test High-to-Low & Ground and Low-to-Ground resistance.
- Criterion: At 20∘C, the insulation resistance for 10kV windings should not be lower than 2000MΩ.
- Polarization Index (PI): R10min/R1min, should be ≥1.3.
- DC Resistance Unbalance Rate:
- Calculation: ΔR%=Rmax−Rmin/Ravg×100%.
- Standard: Phase-to-phase difference ≤2%, line-to-line difference ≤1%.
- Infrared Thermography: Use a thermal imager to scan high and low voltage bushing joints and cable connections to ensure temperature rises are within limits.
4. Root Cause Analysis
Deeply analyze the logic chain behind failures to avoid repetitive maintenance.
- Insulation Aging and Dust: Moist dust layers form conductive paths, significantly reducing the insulation distance at the winding ends.
- Temperature Control Drift: Aging or poor contact of PT100 sensors leads to reading deviations, causing false or missed alarms.
- Loose Connection Bolts: Long-term electrodynamic vibration leads to increased contact resistance at terminals, generating localized high temperatures.
- Core Grounding Failure: Disconnected core clips or multi-point grounding generates circulating currents and heating.
5. Corrective Actions
Execute standardized maintenance actions for identified issues.
- Cleaning Process: Use dry compressed air at 0.2–0.5 MPa to blow out air ducts, and wipe insulation components with anhydrous ethanol.
- Fastening: Use a calibrated torque wrench to retighten all electrical connection bolts (Reference: approx. 45–50N⋅m for M12 bolts).
- Moisture Treatment: If insulation resistance is low, use hot air circulation or infrared lamps for drying to restore insulation performance.
- Controller Calibration: Replace damaged sensors and verify controller accuracy using a standard resistance box.
6. Prevention and Summary
Transform from "reactive repair" to "proactive prevention" through institutionalized construction.
- Maintenance Advice: Increase inspection frequency during high-humidity seasons (e.g., monsoon or rainy seasons) and ensure protective fences are intact and ventilation is good.
- Anti-Accident Measures: Regularly check the transformer room for waterproofing and pest control measures.
- Management Insight: Establish comprehensive equipment archives, record annual preventive test data, and identify trend-based defects through horizontal comparison.
7. Expert Tips
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