Nowadays, transformers are present in multiple sectors, being fundamental parts even in critical processes. Nowadays, there are a series of techniques, tests and trials that allow the operational continuity of these units, as well as associated maintenance and good practices.

Although each installation has different characteristics, the following are the usual ones or the ones that must be complied with in the standard.

• Disconnect the equipment from the mains taking the necessary measures.
•     Check the safety system for overtemperature.
•     Check the safety system for overvoltage in the transformer.
•     Checking the current and earth leakage systems.
•     Checking other indicators
•     Checking the oil level as well as possible leaks.
•     Dielectric rigidity test of the oil
•     Checking, cleaning and adjusting all electrical connections, fixings, supports, guides and wheels, etc.
•     Checking and cleaning insulators
•     Checking the operation of the fans if necessary
•     Cleaning and painting of the chassis, casings, tank and other external elements of the transformer susceptible to rust or residue.

• Measurement tests of the ohmic resistance of the windings.
• Transformation ratio.
• Polarity, angular displacement and phase sequence.
• Vacuum losses and excitation current at nominal voltage.
• Impedance voltage and losses due to load at nominal voltage.
• Dielectric tests:
• Applied voltage
• Induced voltage
• Insulation resistance

• Tests Physical-chemical analysis
• Chromatography of gases dissolved in oil
• Content analysis
• Filtering and degassing process
• Transformation ratio tests
• Insulation resistance tests
• Power factor tests
• Resistance tests
• Revision changers
• Accessory inspection and testing
• Oil change