Transformer Maintenance Tests – Transformer Condition Assessment

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


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