SERVICE · TRANSFORMER OVERHAULING
A comprehensive procedure where the equipment is disassembled, cleaned, inspected and repaired as needed — conducted in response to internal failures or as part of scheduled maintenance.
THE APPROACH
In essence, transformer overhauling entails a comprehensive procedure where the equipment is disassembled, cleaned, inspected and repaired as needed to restore it to standard operating conditions. Overhauling is typically conducted in response to internal failures or as part of scheduled maintenance intervals. This process is more complex for higher-rated transformers.
DIAGNOSTIC INSIGHT
DGA
Buchholz Relay
THE PROCESS
The power transformer inspection phase involves a thorough visual examination of external and internal components — including critical elements like windings, core, bushings, tap changers and cooling systems. Special attention is given to identifying signs of physical damage, corrosion, wear and oil leakage. Advanced techniques, such as ultrasonic testing and thermography, may be used for a more in-depth analysis. The insights from this phase guide decisions on subsequent repairs and replacements, ensuring the transformer’s continued safe and efficient operation.
TESTING
Assess the integrity of insulation materials, identifying any weaknesses or potential breakdown points — crucial for preventing electrical leakage and ensuring safety.
Verify the turns ratio between primary and secondary windings. Deviations from the expected ratio can indicate issues with the core or windings.
Help identify abnormal resistance values in the windings, indicative of issues such as corrosion or damage.
The testing phase is critical for identifying potential electrical issues and verifying that the transformer can operate safely and efficiently in its intended environment.
CLEANING
To remove external and internal contaminants, it’s essential to clean the transformer. Externally, it preserves structural integrity and aids visual inspections. Internally, it ensures optimal performance by preventing overheating caused by dust or deposits. Clean components facilitate accurate diagnostic tests, contributing to overall reliability and minimising the risk of unexpected issues.
REPAIRS
Based on the condition assessment, repairs and replacements of various transformer parts take place:
Critical for insulation and supporting electrical connections — repaired or replaced to maintain optimal performance.
Essential for preventing oil leakage and ensuring a sealed environment — inspected and replaced if necessary.
Worn or damaged insulation materials are repaired or replaced to uphold insulation integrity and prevent breakdowns.
Fans or radiators are inspected and repaired to ensure efficient heat dissipation, preventing overheating.
Decisions on repairs or replacements are guided by the severity of the component’s condition, considering factors such as the transformer’s age and operational demands.
REASSEMBLY
Reassembly involves reconstruction with refurbished or new components. This includes precise alignment, secure fastening with applied torque, sealing for oil integrity, and rigorous quality checks. The emphasis on precision during reassembly ensures the transformer operates within design parameters, enhancing overall performance and reliability.
Critical steps aimed at restoring the insulating oil to optimal condition:
A thorough filtration process removes impurities and contaminants, improving dielectric strength and preventing breakdowns.
Advanced techniques such as degasification remove dissolved gases and moisture so the oil meets stringent standards.
The purified oil is carefully refilled with precise measurements to the recommended level, accounting for temperature and operation.
The transformer is sealed into a closed system, maintaining oil purity and keeping out external contaminants.
The quality of the oil directly impacts the transformer’s ability to withstand electrical stresses and environmental conditions, making this phase essential.
The final phase — a comprehensive evaluation to validate the transformer’s performance and safety after refurbishment:
Assess the effectiveness of insulation materials, ensuring they can withstand electrical stresses and prevent leakage.
Simulate real-world operating conditions, verifying capability to handle specified loads under varying demand.
Evaluate the ability to withstand specified voltage levels without breakdown — a critical measure of insulation integrity.
Validate correct operation of components such as tap changers, cooling systems and protective devices.
After passing all tests, the transformer is commissioned for active service and integrated into the larger power system.
CONCLUSION
