Diagnostic Field Testing and Condition Assessment of Power Transformers in Service

In this era of reformation, liberalization and unbundling of electricity markets, asset management in power sector has assumed greater prominence. Power transformers are key components in any transmission & distribution network and loss of a transformer can have an enormous impact on reliability and availability of power supply and on cost. As society is more and more dependent on electricity for development, the utilities are under pressure to meet the ever-growing demands for reliable power supply. Economic factors are the main consideration and in order to minimize capital expenditure on new equipment, it is a common policy among utilities to maximize the use of existing networks by operating at their design capability. This can be achieved by according importance to the maintenance practice. A survey of the literature indicates that there are more failures of transformer due to poor maintenance, improper operation, severe weather conditions and manufacturing and design defects than due to insulation ageing. The utilities shall have a systematic O & M practice that include diagnostic tests for condition assessment and health checkup of the equipment. The objective of the condition monitoring tests is to detect the first symptoms of incipient faults, ageing development or other problems and monitor their evolution to enable the operator to take appropriate action to avoid major failure. The paper reviews the results of various diagnostic tests including dielectric response methods for condition assessment of power transformers.