Monitoring and diagnostic systems for dry type transformers

For the monitoring and protection of dry type transformers a cost-effective and efficient system has been developed, which monitors online local overheating using a fibre optic sensor technology. The system allows to prevent secondary failures and cost. An offline analysis of the transfer function can give indications on interturn short circuits. The sensitivity is in the range of a few percent of the whole number of windings. This will reduce the maintenance and repair costs. The detection and localisation of partial discharges can be easily carried out with a number of sensors fixed on the surface of the dry type transformer. The measurement of the absolute value of the signals as well as the difference between two adjacent sensor leads to a detection sensitivity in the range of 20 pC even under noisy condition on site which is sufficient for this type of transformers. The introduced system is well tried and installed on different dry type transformers in Germany for more than one and a half year with the intention to increase the reliability and life expectancy of dry type transformers leading to an ensured power distribution.