The Two Core Objectives of Transformer Maintenance
Transformer maintenance serves two purposes. The first is to keep every component in good working condition so that the transformer can operate reliably over its design life. The second is to build a complete historical record of condition, test results and repairs; this record is the basis for diagnosing faults, planning replacements and proving compliance with maintenance standards.
Periodic vs Condition-Based Maintenance
Periodic maintenance performs fixed activities at set intervals regardless of condition, which is simple but can be wasteful. Condition-based maintenance plans actions according to measured condition indicators such as oil quality, dissolved gases, insulation resistance and temperature, and is generally more economical because work is done only when evidence shows it is needed. Most utilities combine both: a minimum periodic inspection plus condition-triggered actions.
Core Maintenance Activities
Visual inspection of the tank, bushings, cooling equipment and accessories.
Oil sampling and analysis, including dielectric tests and dissolved gas analysis (DGA).
Electrical measurements such as winding resistance and insulation resistance.
Equipment tests such as tap-changer operation and protective device checks.
Thermal camera measurement to detect hot spots on connections and bushings.
Offline and online monitoring of oil temperature, winding temperature and partial discharge.
Maintenance Under Energized Conditions
Some activities can be performed while the transformer is in service: checking oil leakage and tank cracks, inspecting the conservator breather and replacing desiccant when it is saturated, measuring connection and bushing temperatures with a thermal camera, and taking oil samples for laboratory analysis. These tasks require trained staff and approved safe procedures for work on live plant.
Maintenance Under De-Energized Conditions
De-energized maintenance follows lock-out, earthing and discharge procedures, and may include: replacing bushing gaskets, cover gaskets and tap-changer gaskets; inspecting welded joints; cleaning bushings with methylated spirit; cycling the tap-changer through its full range; drying, reclaiming or filtering the oil; taking samples from drain valves; treating surface coating defects; and cleaning the gas-relay glass. For dry-type transformers, the main tasks are vacuum cleaning, tightening winding supports and removing humidity from the enclosure.
FAQ
Why is a maintenance record important?
The record shows the history of oil tests, electrical measurements and repairs, which is essential for diagnosing deterioration trends and for warranty, audit and insurance purposes.
What is condition-based maintenance?
It is a strategy where maintenance is triggered by measured condition indicators instead of fixed time intervals, reducing unnecessary work and cost.
Why is dissolved gas analysis used?
DGA detects gases generated by thermal and electrical faults inside the oil, allowing early identification of overheating, partial discharge or arcing.
What is checked during energized maintenance?
Oil leaks, breather desiccant, connection temperatures by thermal imaging and oil samples can be checked while the transformer remains in service.
Which safety steps are required before de-energized work?
Lock-out and tagging, earthing, discharge of stored energy and verification of absence of voltage are required before opening the transformer.
How often should maintenance be performed?
Frequency depends on the transformer age, loading, oil condition and manufacturer recommendations; annual inspection and periodic oil testing are common practice.