What are the common electrical tests for transformers?
What are the common electrical tests for transformers?
Conventional electrical tests for transformers are designed to identify internal faults and primarily include the following:
(1) Voltage Ratio Test:
Used to verify the voltage ratio and determine if there are short circuits between turns or layers, or if switch leads are connected incorrectly.
(2) Winding Resistance Measurement:
Employed to assess the quality of wire welding, detect winding short circuits, poor switch contacts, or incorrect lead connections.
(3) Insulation Resistance and Absorption Ratio (Ro/R₁s) or Polarization Index Measurement:
Utilizing a 2500V megohmmeter to measure the insulation resistance R at 60 seconds and comparing it with the insulation resistance Rs at 15 seconds, this test serves as a sensitive indicator for evaluating insulation degradation and moisture content in transformers. The ratio R/Rs or polarization index also indicates localized defects or moisture levels in insulation paper, bushings, and windings.
(4) tanδ Measurement:
Determines the degree of insulation moisture and defects in the insulation structure by measuring dielectric losses.
(5) Oil Tests:
Internal faults can affect the properties of the oil. Therefore, tests such as dielectric strength, tanδ, acidity level, trace moisture, and gas content in the oil indirectly reflect internal faults in the transformer.
Additionally, withstand voltage tests for transformers can be used to assess the insulation condition between phases and to the ground. Meanwhile, no-load and load tests, by comparing measured values with original values, help determine the presence of inter-turn and inter-phase short circuits in the windings.
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