This article is related to Transformer Maintenance Tests, and what assessment is needed in transformer.
Transformer Condition Assessment Summary – Transformer Maintenance Tests
Following table shows quick summary for this assessment and maintenance of transformer.
| Test | Detects | Tool |
| Online Tests | ||
| Dissolved Gas Analysis | Internal arcing; bad electrical contacts; hot spots; partial discharge; and overheating of conductors, oil, tank, and cellulose insulation | Requires laboratory analysis |
| Oil Physical and Chemical Tests | Moisture, degraded IFT, acidity, furans, dielectric strength, and power factor | Requires laboratory analysis |
| External Physical Inspection | Oil leaks, broken parts, worn paint, defective support structure, stuck indicators, noisy operation, loose connections, cooling problems with fans, pumps, etc. | Experienced staff and binocular |
| External Temperatures (Main tank and load tap changer) | Temperature monitoring with changes in load and ambient temperature | Portable temperature data loggers and software |
| Infrared Scan | Hot spots indicating localized heating, circulating currents, blocked cooling, tap changer problems, and loose connections | Thermographic camera and analysis software |
| Offline Tests | ||
| Double Tests (bushing capacitance, insulation power factor, tip up, excitation current) | Loss of winding insulation integrity, loss of bushing insulation integrity, and winding moisture | Double test equipment |
| Turns Ratio | Shorted windings | Double test equipment or turns ratio tester |
| Short Circuit Impedance | Deformation of the core or winding | Double or equivalent test equipment |
| Core to Ground Resistance (External test may be possible depending on transformer construction) | Bad connection on intentional core ground and existence of unintentional grounds | Megger Tester |
| Winding Direct Current (dc) Resistance Measurements |
Broken strands, loose connections, bad tap changer contacts | Wheatstone Bridge (1 ohm and greater) Kelvin Bridge micro-ohmmeter(less than 1 ohm). |
| Frequency Response Analysis | Shifted windings | Double or equivalent sweep frequency analyzer |
| Internal Inspection | Oil sludging, displaced winding or wedging, loose windings, bad connections, localized heating, debris and foreign objects | Experienced staff, micro-ohmmeter |
| Degree of Polymerization | Insulation condition (life expectancy) | Laboratory analysis of paper sample |