Maintenance methods for dry-type transformers

Cleaning and Maintenance

Dust may be removed from the exterior and interior surfaces of the transformer using a vacuum cleaner, clean cloth, or soft-bristled brush. DO NOT use a wet cloth or alkaline -acid cleaning agents, as they may allow moisture to seep into insulated areas.

Perform cleaning of the cooling fans, filters, and other heat dissipation equipment using the cleaning methods described in the previous bullet to ensure smooth flow of air through the heat dissipation equipment.

Inspection of Fastenings and Electrical Connections

All bolts and terminals should be inspected and if loose, they should have additional torque applied to them, to help avoid the incidence of higher contact resistance and or the possibility of localized heating at a loose terminal.

Inspect the busbars and grounding wires for corrosion (if found, they should be recoded or replaced using Power Compound Grease as a corrosion preventative) and if necessary perform refurbishment on all connection points to maintain current carrying capability.

Testing of Insulation and Conductive Properties

Testing the insulation resistance of the winding-to-ground with an insulation resistance tester (2500 V megaohm meter), the insulation resistance should be equal to or greater than 70% of factory specification.

Regular maintenance testing should perform dielectric loss, dielectric withstand voltage and leakage current to detect insulation deterioration or moisture ingress in a timely manner.

Calibration of temperature sensors, thermistors and other temperature monitoring devices should be performed to guarantee correct monitoring of temperature alarm or trip functions.

Inspection of the cooling system

Be sure to check that the natural ventilation or forced air-cooling method is in proper working condition. Verify that the direction of rotation, speed and noise levels of the fan conform to the proper standards.

If any of the cooling pipes are found to be restricted, or any fans are found to be inoperable, then clean or replace those components immediately.

Lightning Protection Grounding and Safety

Confirm that the lightning protection grounding system is intact, measure the grounding resistance periodically and ensure that overvoltage damage does not occur as a result of poor grounding.

Before commencing any maintenance or repair work, it is mandatory to disconnect, discharge, and ground all power sources. A two-person operation is required and insulated footwear and gloves must be worn. It is unacceptable to touch any internal component until it is properly discharged.

Continuous online monitoring of the operational status is done through temperature, load and current monitoring instruments to identify any abnormalities and issue alarms to shut down for inspection.

All inspections, tests and cleaning are documented with times, staff, results and related information forming a total historical maintenance record available for trending and future planning.

Maintenance recommendations by cycle

An annual maintenance will be executed to perform all of the following inspections; all visible inspections and cleaning, tighten all of the mechanical fasteners, conduct insulation testing, and inspect the cooling system.

Pre-operational Maintenance: All newly installed or long idled (not in service since last serviced) equipment should have pre-operation inspections performed on them and a dehumidification process performed before it is operated.

Inspect equipment that is used in abnormal environments, such as high humidity, high dust, or highly corrosive gas conditions will have inspection intervals shortened appropriately (e.g., inspection every six months).

As a safety precaution against electric shock and backfeed, all work should always be performed in accordance with the safety protocol of being disconnected from power supply and properly grounded.

All professional-grade tools including insulation resistance meters, vacuum cleaners, hot air blowers, etc., must also adhere to specific operating procedures for usage.

When finished with maintenance, the protective device will need to be reset, and the device will not be able to be safely energized again until you have confirmed all checked out properly.

Utilizing the systematic maintenance steps outlined above will extend the functional life of dry-type transformers while maximizing both efficiency and