Winding Deformation Tester is the "orthopedic doctor" and "structural CT" of power transformers. It can accurately diagnose whether the internal winding of the transformer has been twisted, bulged, displaced, or has inter-turn short circuits without the need for lifting the cover or disassembling the transformer.
Combined with the latest industry standards and market dynamics as of March 2026, I have compiled the core principles, latest technology trends, and purchasing guide for this instrument:
1. Core Principle: How does it "see through" the interior?
This instrument mainly uses the Frequency Response Analysis (FRA) method.
Basic Principle: The transformer winding has a unique "fingerprint" characteristic (amplitude-frequency response curve) at specific frequencies. When the winding undergoes mechanical deformation (e.g., due to short-circuit current impact, transportation impact), its internal distributed capacitance and inductance parameters change, causing this "fingerprint" to alter.
Test Method: The instrument injects a series of sine waves of different frequencies (typically 1 kHz - 2 MHz) into the winding, measures the amplitude ratio and phase difference between input and output, and plots the frequency response curve.
Judgment Basis:
Horizontal Comparison: Compare the curves of phases A, B, and C of the same transformer. Under normal conditions, the three phases should have high coincidence. If a phase curve deviates significantly, it indicates deformation in that phase.
Vertical Comparison: Compare the current curve of the transformer with its factory/historical curve. If the difference exceeds the standard (e.g., DL/T 911), it is judged as abnormal.
2. Latest Technology Trends and Standards in 2026
According to the latest industry developments (as of March 2026), winding deformation testing technology is undergoing the following upgrades:
Standard Updates: In addition to the traditional DL/T 911-2004, the industry is gradually implementing stricter new standards (e.g., DL/T 911-2024 and related GB/T guidelines), imposing higher requirements on measurement accuracy and data analysis.
Multi-modal Fusion: High-end models (e.g., TWR series from UHV Electric) begin to combine Frequency Response Analysis (FRA) with impedance measurement. The impedance method can assist in judging the overall deformation degree of the winding, and the combination improves diagnostic accuracy.
Broadband and High Precision:
Frequency Range Expansion: Mainstream equipment now covers 10 Hz - 2 MHz or even wider. The low-frequency band (<1 kHz) better reflects the core and overall structure, while the high-frequency band reflects local deformation.
Accuracy Improvement: Frequency accuracy reaches 0.001%, amplitude accuracy reaches 0.1 dB, enabling detection of minor insulation aging or looseness.
Intelligent Diagnosis: Built-in expert system can automatically calculate the correlation coefficient (R value) and generate conclusions of "normal, mild, moderate, severe" deformation with one click, no longer relying entirely on manual chart reading.
3. Core Functions and Parameter Indicators
Table
Key Indicator Recommended Parameter/Suggestion Description
Scanning Frequency Range 10 Hz - 2 MHz (or 1 kHz - 2 MHz) Wider coverage reduces detection blind spots. Low frequency for overall, high frequency for details.
Scanning Mode Linear sweep + Logarithmic sweep Linear sweep provides higher resolution in low-frequency band, suitable for fine analysis.
Measurement Speed < 60 seconds/phase Key to on-site work efficiency; too slow affects maintenance progress.
Anti-interference Capability Digital filtering + Shielding design The electromagnetic environment at substations is complex; instruments with poor anti-interference produce curves full of "noise."
Data Management USB export + Database management Supports export of Word/JPG reports for archiving and future comparison.
4. Common Application Scenarios
After Short-circuit Impact: After a transformer suffers an outlet short circuit or near-zone short circuit, testing must be performed to confirm the winding is not damaged.
After Transportation and Installation: Large transformers may experience severe vibration during long-distance transportation; testing is required before commissioning.
Before/After Overhaul or Retrofit: Retain as baseline data for future condition assessment.
Sudden Anomaly Investigation: When the transformer experiences differential protection operation but no gas in the gas relay, winding deformation needs to be checked.
5. Purchasing and Pitfall Avoidance Guide
Check "Anti-interference": On-site testing is most afraid of interference. Ask if the instrument has dedicated shielded cables and digital filtering algorithms. If the curve shakes severely in the low-frequency band (tens of kHz and below), the anti-interference capability is poor.
Check "Software Usability": Hardware only collects data; analysis software is the soul. Good software can automatically overlay multiple curves (up to 9), automatically calculate similarity, and directly give diagnostic conclusions.
Check "Origin and After-sales Service":
Wuhan, Hubei (e.g., Wuhan UHV, Moen Intelligent) and Yangzhou, Jiangsu (e.g., Tuopu Electric) are the main industrial clusters.
Considering you are in Yangzhou, there are many local manufacturers (e.g., Yangzhou Tuopu), making after-sales response and calibration very convenient.
Pitfall Avoidance: Do not only look at price. Cheap instruments often have fewer sampling points (rough curves) and low frequency accuracy, easily misjudging normal process deviations as faults or missing serious hidden dangers.
6. On-site Operation Tips
Grounding: The instrument and transformer casing must share a common ground, and the grounding must be good; this is the first step in anti-interference.
Disconnection: Before testing, all high-voltage and low-voltage side leads (including neutral point leads) must be removed, leaving only the test leads.
Contact: The test clips must be firmly clamped onto the bushing terminals; poor contact will cause severe fluctuations in the high-frequency band of the curve (false appearance).
In summary, the winding deformation tester is the "goalkeeper" of transformer condition-based maintenance. It is recommended to choose a model with dual-mode (FRA + impedance), strong anti-interference capability, and intelligent software analysis.
