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1. Maintenance and Repair of
Distribution Transformers
Technical Presentation | September
2025

2. Introduction
• Distribution transformers are essential for
stepping down voltage for end-users. Regular
maintenance ensures reliability, safety, and
longevity.

3. Types of Distribution Transformers
• • Oil-immersed transformers
• • Dry-type transformers
• • Common ratings: 50–1250 kVA, 11–24 kV

4. European Standards & Regulations
• • IEC 60076 series
• • EN 50588-1 (Ecodesign Directive)
• • EN 60296 (Transformer oils)
• • IEC 60364 (Safety)

5. Construction Overview
• • Core and windings
• • Tank and bushings
• • Cooling system
• • Accessories: Buchholz relay, breather, tap
changer

6. Common Faults in Transformers
• • Winding faults: short circuits, deformation
• • Core faults: grounding, loosening
• • Insulation faults: aging, moisture
• • External faults: bushing cracks, cooling
failure

7. Fault Diagnosis Methods
• • Visual inspection
• • Electrical tests: IR, winding resistance
• • Oil analysis: BDV, DGA
• • Online monitoring and AI diagnostics

8. Preventive Maintenance Schedule
Frequency Tasks
Daily/Weekly Visual checks, oil level, temperature
Monthly Clean bushings, check silica gel
Quarterly Oil BDV test, grounding check
Yearly Oil chemical tests, IR test, tap changer service

9. Maintenance Procedures
• • Oil sampling and testing
• • Breather replacement
• • Tightening connections
• • Tap changer inspection and lubrication

10. Repair Practices
• • Minor: gasket replacement, oil top-up
• • Major: winding replacement, core tightening
• • Workshop vs. on-site repair

11. Safety Precautions
• • De-energize before work
• • Lockout/tagout
• • Use PPE
• • Fire safety measures

12. Technical Specifications Example
• • Oil-immersed transformer
• • 11/0.4 kV, 50–1250 kVA
• • ONAN cooling, Dyn11 connection
• • EN 60076 compliant

13. End-of-Life Considerations
• • Oil disposal (EN 62770)
• • Recycling metals and insulation
• • Environmental compliance

14. Future Trends in Maintenance
• • Digital twins
• • IoT sensors
• • Remote monitoring platforms
• • Predictive maintenance

15. Summary & Recommendations
• • Regular inspections
• • Follow EN standards
• • Use qualified personnel
• • Adopt smart maintenance tools

16. References
• • IEC 60076, EN 50588-1, EN 60296
• • Bowers Electricals Manual
• • Pauwels Maintenance Guide
• • ABB Handbook