In preventive testing of oil-immersed or dry-type transformers at 35kV and below, frequency response curves sometimes show repeatability deviations in a certain frequency band, while results for the same transformer tested at different times are inconsistent. Such phenomena are often related to test wiring, excitation signal settings, or data comparison methods. The HZ-FRA300 transformer winding deformation tester adopts the Frequency Response Analysis (FRA) method and is suitable for factory tests, handover acceptance, and periodic testing during operation. The following addresses several key points starting from common comparison questions raised by technical engineers.
Q: How should one choose between the frequency response method and the traditional low-voltage short-circuit impedance method in winding deformation detection?
A: The low-voltage short-circuit impedance method mainly reflects changes in the overall inductance and geometric dimensions of the winding and is more sensitive to inter-turn short circuits and overall displacement; the frequency response method obtains the internal network response of the winding through swept-frequency excitation and is better at capturing local deformation and changes in disc-to-disc clamping pressure. The two are not substitutes for each other. In the field, the frequency response method is usually used as a screening tool for winding deformation, and when necessary, it is combined with short-circuit impedance or no-load tests for comprehensive judgment. The HZ-FRA300 adopts the frequency response analysis method in accordance with DL/T911-2016 and IEC60076-18, and is suitable for establishing winding frequency response fingerprints during periodic testing for longitudinal comparison.
Q: What should be noted at each stage of longitudinal comparison during test data comparison?
A: The prerequisite for longitudinal comparison is consistent test conditions. The excitation signal amplitude, wiring positions, grounding method, and tap changer position should all remain the same as in the original records. If the original spectra are missing, lateral judgment can also be made by comparing frequency response differences among the three-phase windings of the faulty transformer, but attention should be paid to the inherent differences caused by asymmetric three-phase structures. The HZ-FRA300 supports storage and retrieval of frequency response curves in data management. Ambient temperature and wiring method should be recorded on site to facilitate exclusion of external variables during subsequent retesting.
Q: How does the USB data transmission stage affect testing efficiency?
A: Data transfer between the instrument and the computer relies on USB interface driver support. In the application software, the driver is used to complete downlink control and uplink acquisition of frequency response data. If connection recognition abnormalities occur on site, check whether the driver files are complete and whether the interface power supply is stable. The HZ-FRA300 adopts a general USB communication architecture in the data transmission stage. Before testing, it is recommended to confirm that the computer has correctly recognized the device ID to avoid test interruption caused by driver loading failure.
For factory and preventive testing of transformers at 35kV and below, the value of frequency response method testing lies in establishing a traceable baseline of winding condition. During selection and use, attention should be paid to the instrument's ability to control the sweep frequency range and excitation amplitude stability, as well as the usability of the data comparison software, rather than pursuing a single indicator alone. The repeatability of on-site testing often explains more than the numbers on a parameter sheet.
