Electrical Field Testing on Power Transformers

They are routine tests recommended by the IEEE StdC57.12.00-2006, they are carried out periodically or
under a particular circumstance. The characteristics of a transformer are mostly affected with time, due
to multiple events that can be from different origins. Electrical origin: internal overvoltage, atmospheric
discharges, and internal discharges; Thermal origin: overloads, over-excitation and lack of refrigeration;
Mechanical origin (short circuits, vibrations, shocks, transports) and of Physical origin (moisture ingress,
aging wear, and corrosion).
Check that the design characteristics of a transformer are maintained throughout its life, evaluate the
effect during an event, schedule interventions (condition-based maintenance, repairs, or replacements),
or avoid catastrophic failures.
Measure the insulation resistance between windings and between them (individually) and ground.
Confirm the performance of the windings in regards to the design or plate characteristics.

Process:

Measurement of the insulation resistance.
Measurement of the insulation power factor and capacitance.
Measurement of winding resistance.
Measurement of the transformation ratio.
Measurement of excitation current.