After transformer handover or maintenance, if only a single method is used to assess winding condition, when the deviation between the short-circuit impedance value and historical data exceeds 2%, it is often difficult to determine whether it is winding deformation or a difference in test conditions. When selecting a model, attention should be paid to whether the instrument supports multiple test principles and has good frequency response consistency.
The sweep frequency range is recommended to cover 0.5kHz～2MHz to capture the response characteristics of the winding in different frequency bands. The sweep method can be linear or logarithmic, and the sweep interval and number of points can be set arbitrarily, making it easy to optimize resolution for transformers of different capacities. The frequency accuracy is better than 0.001%, and the dynamic range is -120dB～+20dB, which can clearly distinguish the amplitude-frequency curve shift caused by small deformation. The instrument should have built-in reference curves of DL/T911-2016 and IEC60076-18 standards to assist rapid on-site comparison.
By short-circuiting the low-voltage side and applying a low voltage to the high-voltage side, the short-circuit impedance value of the transformer is measured. This method is more sensitive to inter-turn short circuits and overall deformation, and complements the sweep frequency method. When selecting a model, it is necessary to confirm that the instrument can simultaneously record voltage, current, and impedance values, and support historical data trend analysis to avoid misjudgment caused by a single measurement error.
The instrument should have anti-interference capability and be suitable for on-site use in substations. The test wiring is simple, and it supports one-key acquisition and automatic saving. The accompanying software should be able to generate amplitude-frequency response curves and impedance comparison charts, and export reports in standard formats. For technical engineers, it is recommended to prioritize models with self-check functions and the ability to store multiple sets of test data, facilitating long-term tracking of winding condition.
