Hazards of Dry-Type Transformer Winding Deformation

1. Limitations of Early Detection Methods

(1) Lumped Parameter Detection Method

• Core Issue: Only capable of diagnosing severe winding deformation, with poor sensitivity to early minor deformation.
• Operational Drawback: Complex operation， requiring precise parameter calibration and vulnerable to external interference.

(2) Cover-Opening Inspection Method

• Core Issue: Cannot accurately identify internal winding deformation (e.g., subtle displacement, turn-to-turn short circuits) that is not visible to the naked eye.
• Practical Drawback: High operational difficulty, consuming substantial manpower and material resources, and requiring transformer shutdown—disrupting normal power supply.

2. Current Mainstream Winding Deformation Detection Methods

(1) Low-Voltage Pulse Analysis Method (Core Universal Method)

• Core Principle: Input a stable low-voltage pulse signal at the winding terminal, synchronously record voltage waveform data at the signal end and other terminals, and compare time-domain signal changes between the excitation end and response end.
• Detection Logic: Winding deformation causes synchronous changes in internal capacitance and induced equivalent parameters, altering the winding’s inherent characteristics. By inputting the same low-voltage pulse signal, winding state information is derived from response signal differences before and after deformation.
• Key Advantage: Serves as a general method for testing dry-type transformer short-circuit withstand capacity, with high sensitivity to minor deformation and simple operation.

(2) Short-Circuit Impedance Test Method

• Core Principle: Measure the winding’s short-circuit impedance value (Zk) and compare it with the initial factory value or standard threshold.
• Detection Logic: Winding deformation (e.g., axial displacement, radial bulging) changes the magnetic flux distribution, leading to deviations in short-circuit impedance.
• Application Scope: Suitable for on-site rapid screening, especially for obvious mechanical deformation.

(3) Frequency Response Analysis (FRA) Method

• Core Principle: Apply a wide-frequency AC signal to the winding, measure the frequency response curve (amplitude-frequency/phase-frequency characteristics), and compare it with the baseline curve.
• Detection Logic: Winding deformation alters its distributed parameter network (resistance, inductance, capacitance), resulting in shifts or distortions in the frequency response curve.
• Key Advantage: High accuracy for early subtle deformation, capable of quantifying deformation degree.

(4) Vibration Analysis Method

• Core Principle: Collect the transformer’s operating vibration signals (via sensors), analyze frequency spectrum characteristics, and identify winding deformation.
• Detection Logic: Normal windings have stable vibration frequency components; deformation causes new vibration peaks or amplitude changes due to uneven electromagnetic force.
• Application Scope: Non-intrusive detection, suitable for online monitoring without shutdown.

3. Core Application Suggestion

• For on-site routine inspection and short-circuit withstand capacity testing: Prioritize the low-voltage pulse analysis method for its simplicity and reliability.
• For early subtle deformation diagnosis and precision testing, Adopt the frequency response analysis method to ensure no hidden dangers are missed.
• For rapid screening during operation: Use the short-circuit impedance test method or vibration analysis method to avoid power supply interruption.