Coordination and control of tap changers under load at different voltage level transformers

Tap changers under load (TCULs) of interconnection autotransformers and distribution transformers play an important role in distribution and subtransmission networks voltage control. This paper deals with the problem of coordination and control of such devices in their simultaneous operation. The interaction between TCULs action in transformers connecting different voltage levels and the related effects on voltage patterns is analyzed by means of a simplified model. Some strategies for TCULs operation are considered and the optimal ones are identified for achieve both adequate security levels in transmission network operation and supply quality. Finally a criterion for setting coordination of TCULs voltage regulators in simultaneous different voltage levels TCULs automatic control is proposed and discussed