All transformers require continuous inspection to ensure the proper functioning of the equipment. And the electrical transformers, which are used in the generation and distribution of energy for industries, hospitals, airports, and cinemas, are no different. However, it's worth highlighting that they require specific tests, which allow for the prevention of unscheduled shutdowns, extending the equipment's lifespan, and forecasting maintenance needs, thereby reducing the downtime. Do you know how preventive maintenance for dry-type transformers is performed? Understand below the routine tests, according to Brazilian standards (ABNT – NBR 5356).

Learn how preventive maintenance is performed on dry-type transformers

As previously mentioned, the goal of preventive maintenance is to assess the equipment, understanding its integrity and potential for failure. This is done through various tests that compare the equipment's results with factory (design) data and in accordance with Brazilian standards. Check out the step-by-step process below. 

Site inspection and cleaning

Analysis of the transformer installation site, visual inspection of the equipment, temperature check, and cleaning of air inlets and outlets. 

Noise presence check

Monitoring of the sounds produced by the equipment and comparison with the expected in the project. 

Turns ratio test
Its purpose is to ensure that the number of turns between windings is in accordance with the design. This ensures that the input and output voltages are maintained within a range of plus or minus 0.5% between the actual and designed values. 

Ohmic resistance test of windings

The essay aims to Analyze possible interruptions or connection and contact issues. It performs this diagnosis  when comparing the calculated values as ideal in the equipment design versus the values measured on it. 

Insulation resistance test
The objective is to verify the solid insulation levels of transformers between windings and ground, which can be compromised due to the presence of dust, moisture, and material degradation.

Applied Stress Test
This involves applying a specific voltage to the equipment at intervals determined by the standard. During the process, to ensure the transformer is functioning as expected, there must be no insulation breakdown.

Induced Tension Test

The test consists of applying double the nominal voltage, with a frequency of at least 120Hz for the time calculated by the standard. During this period, there should be no disruptive discharges. If they occur, the equipment requires maintenance. 

No-load test and excitation current

Perform loss measurements through nominal voltage and frequency, and compare the obtained values with the design and standard.

Are you looking for a qualified company to perform preventive maintenance on dry-type transformers? Transformadores União's laboratory has modern, calibrated, and prepared equipment to validate medium and low voltage transformer tests, as required by ABNT standards. Contact us!