According to DL/T 911—2016 "Frequency Response Analysis Method for Power Transformer Winding Deformation," when a winding undergoes axial or radial deformation, its internal distributed inductance and capacitance parameters change accordingly, and the frequency response characteristic curve exhibits shifts, distortion, or resonance point drift in the corresponding frequency bands. In on-site comparison, if the curve correlation coefficient is below 0.95, it usually indicates a structural change requiring attention. The low-frequency band (1 kHz–100 kHz) reflects overall deformation, the mid-frequency band (100 kHz–600 kHz) corresponds to local bulging, and the high-frequency band (600 kHz–1 MHz) is related to inter-turn or lead displacement. Insufficient test frequency band coverage or improper selection of excitation voltage may cause missing information in characteristic frequency bands, affecting the completeness of the basis for judgment.
The HZF-9100 uses swept-frequency excitation with an output frequency range of 1 Hz–2 MHz, fully covering the three characteristic frequency bands mentioned above. The device offers three excitation voltage options: 10 V, 20 V, and 50 V, adapting to different winding impedances: lower voltage is selected for low-impedance windings to avoid saturation, while higher voltage is selected for high-impedance windings to improve signal-to-noise ratio. Each test channel is acquired independently, and with the host computer software, amplitude-frequency and phase-frequency curves are generated, supporting comparison with historical data or lateral comparison among three-phase windings of the same model. Main technical parameters: frequency accuracy ±0.01%, amplitude measurement range -80 dB to +20 dB, amplitude accuracy ±0.5 dB, single full-frequency scan time no more than 60 seconds, and storage capacity can save more than 200 sets of test curves.
During on-site operation, connect the excitation end and response end to the transformer bushing or winding terminals respectively, and the device automatically completes frequency point scanning and data recording. The software has built-in functions for calculating curve correlation coefficients and comparing three-phase consistency, allowing test personnel to determine whether deformation is suspected based on standard limits. Results are exported in the form of curve graphs and parameter tables, facilitating archiving and subsequent retest comparison. This workflow is suitable for handover acceptance, post-short-circuit diagnosis, and periodic preventive testing of 35 kV–500 kV power transformers, and can also be used for frequency response characteristic testing of reactors, generator stator windings, and other similar structures.
