Defining technical characteristics of new step-up transformers for HPP Kraljevac
Abstract
The paper deals in detail with the selection of optimal technical characteristics of new block transformers for the Kraljevac HPP that should have on-load voltage regulation. The requirements of the transmission network (specific local conditions) are considered, as well as the limitations of the existing (very old) generators. Namely, the optimal choice of, among other things, the transmission ratio, short-circuit voltage and the scope (and method) of on-load voltage regulation of the block transformer must reconcile the requirements of the network with the available generator capabilities (which are partly contradictory). The requirements of the transmission network are considered in detail, from the aspect of voltage conditions (including expected temporary overvoltages), power flows, short-circuit currents, etc. The existing generator limitations are also analyzed, from the aspect of the operating map, voltage regulation, excitation limiter settings, etc. All three different types of transformer voltage regulation (CVFF, VFVV and CbVV) are analyzed through various unfavorable expected operating scenarios. The selection of the following technical characteristics of the block transformer is examined in detail, among other things: rated power, short-circuit voltage, rated voltages and rated winding currents, rated transmission ratio, voltage regulation range (step and number of tap positions), type of voltage regulation, allowed overexcitation, cooling requirements, allowed losses, etc. Finally, the paper also calculates and selects the technical parameters of the current transformer in the star point of the HV winding of the observed block transformer.
