The table below outlines the common tests within these categories for a quick overview:
| Category | Test Type | Primary Purpose |
|---|---|---|
| Insulation Tests | Insulation Resistance & Absorption Ratio | Checks the quality of winding insulation and detects moisture. |
| Dielectric Loss Factor (tanδ) | Measures dielectric power loss in the insulation. | |
| Leakage Current Test | Assesses the condition of insulation under DC voltage. | |
| AC/DC Withstand Voltage Test | Verifies the main insulation strength to ensure it can withstand overvoltages. | |
| Insulating Oil Test | Analyzes the quality and breakdown voltage of the insulating oil. | |
| Dissolved Gas Analysis (DGA) | Detects and analyzes fault gases in the oil to identify internal faults. | |
| Characteristic Tests | Winding DC Resistance | Checks for issues like poor connections, broken strands, or contact problems in windings. |
| Voltage Ratio (Turns Ratio) | Verifies the correct turns ratio and the proper operation of tap changers. | |
| No-load Current & Loss | Evaluates the core's magnetic circuit and identifies faults like inter-turn shorts. | |
| Short-Circuit Impedance & Load Loss | Determines the copper losses and impedance voltage, crucial for short-circuit withstand capability. |
🔧 Specialized and Diagnostic Tests
For a more in-depth analysis, especially for fault diagnosis on larger transformers, several specialized tests are used:
Frequency Response Analysis (FRA): Used to detect mechanical deformation or displacement within the transformer windings by analyzing their transfer function.
Sweep Frequency Response Analysis (SFRA) is a specific method for this purpose.
Polarization Index: A more detailed assessment of insulation health, calculated as the ratio of insulation resistance at 10 minutes to resistance at 1 minute.
Winding Deformation Detection: This involves analyzing vibration signals or using frequency response methods to identify physical changes in the winding structure.
Degree of Polymerization (DP) Test: Measures the mechanical strength of the cellulose insulation (paper) to determine the extent of insulation aging.