engleski

Effectiveness of on-site diagnostic for prevention of fault on transformers

On-site diagnostic testing of transformers is used in order to verify the condition of the transformer. Application of various diagnostic measurements (methods) increase the reliability of operation and reduces maintenance costs. Timely detection of a possible failure reduces the cost of repair. Determining the degree of failure, and possible ways to repair the same, is one of the most important tasks of on-site diagnostics. In recent years, the development of control, measurement and computer techniques has increased the level of development of the monitoring system of transformers. The system is automated and continuously monitors a considerable number of parameters in the transformer, and compares some of the measured values with reference values. Due to the high cost of such a system it is now installed only on the transformers of the exceptional importance, transformers with high power and high voltage levels, and transformers essential for stability of the entire electricity network. As transformer monitoring systems do not measure all the parameters as diagnostic tests, it is necessary to do periodic diagnostic off-line measurements (2-4 years) on the transformers on the site. This measurement is performed by portable devices for measurement of electrical, mechanical and ultrasonic values. Factory acceptance tests (FAT), site acceptance tests (SAT) or the last performed on-site diagnostic measurements are used as reference values for current diagnostic measurements. Number of measurements and methods for determining the condition of the transformer is quite large. Today measurements can be divided in three groups: the standard scope of the measurements, an expanded range of tests and specific diagnostic methods to be used for analysis of the fault. The paper contains a few failures that were found during periodical checks of the condition of the transformer. The examples will show how the continuous and timely diagnosis in the field is very effective in detecting potentially large transformer faults before they appear. Timely detection of potential failures prevents large emergency events, or loss of transformers from the service for a longer period and reduces the cost of repair of defects found. The paper describes a diagnosis cases by using two diagnostic methods: measurement capacitance and dissipation/power factor of bushing insulation system and winding resistance measurement.

diagnostic tests, transformers, winding resistance, bushing, on-site diagnostic, measuring, power factor

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