What are the routine electrical tests for transformers?

a. Voltage Ratio Test: Used to verify the voltage ratio and detect faults such as winding inter-turn or inter-layer short circuits, and check if switch leads are connected incorrectly.

b. Winding Resistance Measurement: Determines the quality of wire welding, detects faults such as winding short circuits, poor contact of switches, or incorrect lead connections.

c. Insulation Resistance and Absorption Ratio (Ro/R₁s) or Polarization Index Measurement: Measures the insulation resistance R at 2500V for 60 seconds and compares it with the insulation resistance Rs at 15 seconds. This is a sensitive indicator for assessing transformer insulation degradation and moisture levels. The ratio of R/Rs or polarization index can also indicate local defects or moisture conditions in insulation paper, bushings, and windings.

d. tanδ Measurement: Determines the degree of insulation moisture and defects in the insulation structure through dielectric loss.

e. Oil Tests: Internal faults can affect the properties of oil. Therefore, tests such as oil breakdown voltage, tanδ, acidity, trace moisture, and gas content are conducted to indirectly reflect internal faults in the transformer.

In addition, the withstand voltage test is used to assess the insulation conditions between phases and to ground. On the other hand, no-load and load tests involve comparing measured values with the original values to determine whether there are faults such as inter-layer or inter-turn short circuits in the windings.

LuShan, est. 1975, is a Chinese professional manufacturer specializing in power transformers and reactors for 49 years. Leading products are single-phase transformer, three-phase transformers, DC inductors, AC reactors, filtering reactor, expoxy resin high-voltage transformer and intermediate, high-frequency products. Our transformers and reactors are widely used in 10 application areas: rapid transit, construction machinery, renewable energy, intelligent manufacturing, medical equipment, coal mine explosion prevention , excitation system, vacuum sintering, central air conditioning.

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