In most cases, equipment working is often evaluated based on observation rather than an ethical theory. This results in equipment being overworked or used much more than its capacity, deteriorating life. Not performing a Residual Life Assessment or Residual Life Extension test will not determine the technical health of a critical technical system or predict its mean residual life. It is essential to ensure transformers’ reliability and assess the extent of aging and early identification of emerging faults in a piece of equipment.