Synthesis of an equivalent dynamic model for load areas with LTC transformers

This paper proposes a procedure for determining an equivalent dynamic model of a sub-transmission network. The dynamic behaviour of the area to be reduced is provided by regulators of LTC transformers feeding a static load. First it is assumed a suitable topology of the 132 kV area and a procedure for reporting static load expressions at the ideal primary winding of the transformers is defined. With the hypothesis of a complete parameter knowledge of the sub-transmission area, an approximated nodal reduction is actuated. Then a modal equivalent is also determined by assuming a dynamic coherence of the tap changer regulator dynamics. The complete procedure is finally validated and criticised by some simulations on this kind of sub-transmission configuration area typical of the Italian network.