Electrical test of transformers

Electrical tests of transformers
"Power transformers are one of the most important parts of an electrical installation. This is the reason why, electrical tests are imperative:
before each start-up for new transformers
When decommissioned for periodic maintenance
When it comes to diagnosing a transformer that has experienced an electrical fault.

The main tests carried out on transformers:
The measurement of transformation ratios as a function of the positions of the load or vacuum adjusters, the no-load currents and the hourly index.
The measurement of the resistances of the primary windings as a function of the positions of the load or no-load adjusters (with the verification of the state of the load adjuster contacts and of the winding continuity).
Measuring the resistances of secondary windings (and tertiary for transformers with three windings)
Measuring short circuit impedances
Measurement of specific winding losses (Tangent delta)
The measurement of excitation currents.
Measuring voltages to check the magnetic balance (Magnetic Balance).
Measuring the dielectric response of the transformer with Omicron Dirana equipment.
Measuring the frequency response of windings with Omicron FRAnalyser equipment
Measuring the insulation of the windings and the magnetic circuit, using a megohmmeter.
Demagnetization of the magnetic circuit of the transformer
Tests of transformer internal protections (Buchholz tansfo, Buchholtz adjuster, suppression, oil temperature and winding, non-return valve and oil level)
Manual and automatic ventilation functional tests
Functional test of the load adjuster.
CT Bushings test (ratios, polarity, saturation curve, winding resistance and insulation measurement).