- What is the standard maintenance interval for transformers?
Based on the nature of maintenance work, transformer maintenance is categorized into overhauls and minor repairs. Conventionally, oil-immersed transformers requiring oil draining and core lifting (or bell jar opening) for inspection are classified as overhauls. Conversely, those needing no oil draining or core lifting, with only external maintenance, oil replenishment, or oil treatment, are termed minor repairs.
1. Major Overhaul Cycle of Transformer in Operation
The overhaul cycle for operational transformers shall comply with the following provisions in DL/T573-2010 'Guidelines for Power Transformer Maintenance':
A. The overhaul cycle for transformers should generally be over 10 years. If a transformer fails during operation or exhibits abnormalities during preventive testing, core lifting for maintenance should be performed in advance as needed.
B. Based on the structural characteristics and manufacturing conditions of transformers, the impact of inrush short-circuit fault currents during operation, daily load conditions, and data from previous electrical tests and oil analysis, the schedule for advance overhauls or extended overhaul intervals can be adjusted as appropriate. For instance, fully sealed transformers are typically only overhauled when severe oil leakage occurs or internal faults are confirmed.
C. The on-load tap changer of transformer should be overhauled after the specified operation times or when defects are found.
2. Minor Repair Cycle of Transformers
The transformer minor overhaul should be carried out once every 1-3 years. The minor overhaul frequency may be increased for transformers installed in particularly polluted environments.
- How to deal with transformer insulation damage?
1. Inspect transformers in operation for oil leakage at any location. Ensure no water accumulation in the transformer body to prevent moisture and air ingress, which may cause insulation damage.
2. The oil seal of the transformer's breather should maintain a proper oil level and ensure unobstructed flow, while the desiccant must remain dry to guarantee optimal moisture absorption.
3. Perform regular inspections to ensure the explosion-proof membrane and safety pressure relief valve of the transformer are in good condition, preventing direct air contact that could increase water content in the transformer oil and degrade its insulation properties.
4. When performing oil replenishment for transformers, ensure the oil quality in the storage tank meets specifications to prevent deterioration. Additionally, avoid replenishing from the transformer's bottom oil tank to prevent air and impurities from entering the transformer, particularly metal contaminants.
5. When the light gas protection activates and signals, immediately collect gas samples for composition analysis and oil samples for chromatographic analysis to identify the cause and resolve the issue promptly.
6. The light gas protection system for operational transformers must be reliably activated. It is strictly prohibited to operate unprotected transformers. If temporary deactivation of the protection is required for operational needs, appropriate measures must be implemented, and the system should be promptly restored afterward.
7. Monitor transformer winding temperature and upper oil temperature closely. When approaching alarm thresholds, conduct a comparative analysis of load, cooler, and ambient temperatures, then implement effective control measures to promptly detect potential internal transformer faults.
8. Carefully inspect the oil flow indicator's position. If the submersible pump stops, immediately restart it to prevent rapid oil temperature rise that could endanger transformer operation.
9. Regularly check the transformer's surge arrester action recorder and maintain accurate records of operation counts. Upon detecting arrester activation, immediately shut down the transformer and perform a thorough inspection.
10. Special attention should be paid to inspecting the bolt securing the transformer's oil sampling port to prevent oil leakage caused by loose bolts after sampling by maintenance personnel.
11. After a transformer trips due to internal fault, immediately disconnect the oil pump and halt its operation to prevent contaminants like free particles or metal fragments from entering the non-faulted sections of the transformer.
12. Prevent excessive coil temperature in transformers, insulation degradation, and burnout. Implement reasonable control of top oil temperature rise during operation.
Especially for the transformer with forced oil circulation cooling, when the upper oil temperature rise exceeds the allowable value, the load should be controlled quickly, and the oil temperature rise should be kept within the specified range, otherwise the transformer will be reduced in load.
During the operation of transformer overload, the oil temperature rise must be closely monitored within the specified value, and the load should be compressed as much as possible to reduce the time of overload operation, so as to prevent the accelerated aging of insulation caused by long-term high temperature operation.