An effective procedure for voltage control in HV systems receiving remarkable energy from DG

The high levels of energy produced by Distributed Generation (DG) may create some problems to the voltage control of transmission systems if a great amount of active power crosses transformers and autotransformers from lower to higher voltage level (reverse power flow). In addition DG is usually intermittent and often does not participate to the voltage regulation process. This situation may be accepted as long as the power from renewable sources (wind and solar PV) is much lower than the power generated by conventional power stations. However, due to the large amount of DG now installed, in such situations as favorable weather conditions and low electrical load, the production from traditional power plants might become negligible compared to the production from distributed renewable sources. Under these conditions, which are occurring more and more frequently in Italy, the blackout risk becomes increasingly high. The present work shows that DG increase is not only just another problem to solve, but it can also be seen by the system operator as an opportunity to adopt proactive actions towards an effective voltage control. With this in mind, the use of a practical procedure is suggested whose validity was demonstrated first theoretically and then through a number of field tests which were suitably reported and commented.