Condition Monitoring of Zigzag Transformers in Composite Transmission Lines for Enhanced Transfer of Combined AC and DC Power

Renewable energy sources have high penetration in today's power grid. Efficient transfer of DC power using existing AC transmission infrastructure is an economically viable means to use renewable energy sources. On the other hand, in AC power transmission, complete utilisation of the transmission line capacity is seldom possible as sufficient margins have to be maintained for transient stability. Composite transmission system facilitates combining AC and DC transmission using zigzag transformers to load the existing transmission line very close to their thermal stability limit. It thereby allows a higher transfer of power through the existing transmission infrastructure. However composite transmission system is vulnerable to transformer saturation under some operating conditions which hamper the power transmission. Hence real time monitoring of the magnetic health of the transformer is necessary to ensure reliable operation of the composite transmission system. This paper proposes a monitoring system wherein the measurements at the transformer terminal are used to assess its magnetic health. A support vector machine classifier is trained to classify the measurements into various operating conditions.