Abnormal Failure Rate on High Voltage Current Transformers Affected by Environmental Conditions

The Mexican Grid has been severely affected by numerous failures on 230 kV and 400 kV Substations Current Transformers (CT´s). The failure rate increased in the latter years and became extremely critical. Several studies and laboratory tests on aged CT´s were carried out to identify the main factors and mechanisms that contribute to the progressive deterioration of the oil paper insulation system. It is important to identify those apparatus with a high failures risk; therefore, an attempt to classify their conditions was performed. The results are shown in this paper.