The life of a transformer consists of many steps from initial specification, design and manufacture through installation, operation, maintenance, and possible change of state with reconditioning and, eventually, replacement. A model of the life of a transformer may be presented as a change of its condition, namely as reduction of safety margin with time under impact of thermal, electric, electromagnetic and electrodynamic stresses and contamination.
Economic as well as technical and strategic factors determine the effective end of life of equipment. A technical life may be still continue until a transformer retains its functional serviceability that may be determined by its four key properties:
- Electromagnetic ability and integrity-an ability to transfer electromagnetic energy at specified conditions, without general overheating and localized hot spots, excessive losses, gassing, excessive vibration and sound.
- Integrity of current carrying circuit.
- Dielectric withstand strengthunder the influence of the specified operational stresses, considering a permissible level of deterioration.
- Mechanical withstand strengthunder the effect of specified through-fault currents.
A failure occurs when the withstand strength of the transformer with respect to one of its key properties is exceeded by operating stresses
