Avoiding adverse interactions between transformer tap changer control and local reactive power control of distributed generators

Local reactive power control of distributed generators (DG) can be used to mitigate the voltage rise effect caused by themselves. In this paper, dynamic interactions between local voltage controllers of the DG units and transformer on load tap changers (OLTCs) are studied using time domain simulations. Studies are conducted with different control modes of DG unit and OLTC control and also secondary substation tap changers are considered. Several types of adverse interactions are identified in the simulations: unnecessary OLTC operations can occur, reactive power transfers can unnecessarily increase and consecutive tap changer operations can occur in case of cascaded OLTCs. The paper gives also some general planning guidelines to avoid the adverse interactions identified in the simulations.