It injects a swept frequency signal into the transformer winding and measures its frequency response characteristic curve. Since minor changes in the geometric structure (inductance, capacitance distribution) of the transformer winding (such as displacement, distortion, inter-turn short circuit) can cause significant changes in the frequency response curve, this instrument is known as the “CT/MRI” of transformers, capable of diagnosing internal mechanical damage without lifting the core. Combined with the latest technical standards in 2026 (DL/T 911-202X revision) and industry applications, the following is an in-depth guide: 1. Core Working Principle Sweep Frequency Method: The instrument performs a sinusoidal sweep over a wide frequency range (typically 10Hz - 2MHz or higher) on the transformer winding. Impedance Spectrum Analysis: Measures the ratio of input voltage to output voltage (amplitude-frequency characteristic) and phase difference (phase-frequency characteristic). Fingerprint Comparison: Compares the measured curve with original factory data, historical data, or cross-phase data of the same model. Low Frequency Band (1kHz - 100kHz): Reflects overall winding deformation (e.g., axial displacement, inter-disk shift). Medium Frequency Band (100kHz - 600kHz): Reflects local winding deformation (e.g., distortion, bulging). High Frequency Band (>600kHz): Reflects lead displacement, inter-turn short circuit, or poor tap changer contact. 2. New Technology Trends in 2026 With the integration of AI and big data technology, modern winding deformation testers have evolved from mere “drawing tools” to “intelligent diagnostic experts”: AI Intelligent Diagnostic Algorithm: No longer relies solely on manual visual inspection of curve differences. Built-in deep learning models automatically calculate correlation coefficient (R), standard deviation (SD), root mean square error (RMSE), and directly provide conclusions of “normal”, “mild deformation”, “severe deformation” along with confidence levels. Anti-interference Capability Upgrade: For the complex electromagnetic environment of substations, digital filtering, spread spectrum technology, and adaptive noise reduction algorithms are used to obtain smooth curves even near live equipment or under strong interference. Multi-terminal Synchronous Testing: High-end models support simultaneous three-phase excitation and synchronous acquisition, eliminating errors caused by temperature and tap changer position differences due to different test times, greatly improving the accuracy of three-phase cross comparison. Cloud Database: Test data is automatically uploaded to the cloud, establishing a “health record” for the transformer throughout its lifecycle, enabling cross-regional and cross-time trend analysis. 3. Key Selection Parameters Frequency Range: Must cover 10Hz - 2MHz (some high-end models up to 5MHz or 10MHz), with higher resolution preferred (e.g., logarithmic steps). Dynamic Range: ≥ 100dB to ensure capture of weak resonant peak and valley changes. Accuracy: Amplitude accuracy ±0.5dB, phase accuracy ±1°. Interface and Protection: Equipped with dedicated low-noise test leads (excellent shielding performance), host protection level IP65 or above, suitable for outdoor harsh weather. Software Functions: Must support three-phase overlay comparison, historical data import, and automatic generation of analysis reports compliant with DL/T 911 standards. 4. Mainstream Brands and Manufacturers Recommended in 2026 This field is highly specialized, with the market mainly composed of domestic high-voltage testing leaders and some international high-end brands. First Tier: Domestic Leaders (High market share, advanced algorithms) Wuhan UHV Electric Power Technology Co., Ltd. Position: Industry dominant player, its BDS series winding deformation testers are widely used by State Grid, China Southern Power Grid, and major power generation groups. Features: Strong AI diagnosis: Built-in latest intelligent evaluation algorithm can automatically identify deformation type (axial/radial). Excellent anti-interference: Stable performance under strong interference in 500kV substations. Complete ecosystem: Software supports integration with PMS system, convenient data management. Shanghai Shenggao Electric / Wuhan Dingsheng Electric Features: Focus on portability and human-machine interaction, lightweight instruments, smooth touch screen operation, suitable for frontline teams with frequent mobile operations. Its “three-phase synchronous test” function stands out among similar products. Yangzhou Huimin Electric / Jiangsu Sutong Electric Features: High cost performance, durable. For routine testing of 110kV and below transformers, its accuracy fully meets requirements, making it a frequent procurement target for grassroots power supply bureaus. Baoding Tianwei / Xinnuo Features: Relying on the transformer manufacturing base, deep understanding of transformer internal structure, its analysis software has unique advantages in fault location (specific winding, specific phase).
