Var control considerations for the design of hybrid distribution transformers

The demand of reactive power in the last mile of the networks is increasing by the time due to the change of loading types by time, beside increasing the total demand itself where new technologies are being introduced depend mainly on different types of electrical support such as electrical cars and more electronic devices in consumption process [1]. This expected situation would lead to take into consideration new approaches in the last mile substations in order to mitigate the drawbacks of the conventional legacy and that by providing more functions in the last mile substations that could provide more flexibility and functionality regarding voltage level, reactive power (RP), amount of demand and losses [1]. This paper focuses the light on the consideration that are taken in designing a distribution transformer that provide additional abilities in regulating the voltage and controlling the RP that is injected in the distribution network (DN) by using a fractional rated converter that is attached partially with the windings of the transformer. This approach aims mainly to enhance the unit with more flexibility in controlling the flow the of the RP at the last mile of the network in order to decrease the losses that are caused by transmitting RP through long transmission networks. The design of the power electronics (PE) modules is detailed and its functionality in compensating Var power is discussed. This approach contributes in meeting the future expectations of the low voltage (LV) networks changes and loading, this contribution is comprised of providing the substation unit with fractional rated power electronic converter that is attached partially with the winding of the LV transformer to provide the load with a specific level of its demand from RP, whereby the solid state switches are controlled according to the immediate need for Var control and support in low voltage (LV) networks [1].