Serviço ancilar de potência reativa de geradores síncronos: aspectos técnicos e regulatórios

Abstract

This work analyzes the technical and regulatory aspects of reactive power supply ancillary services of synchronous generators and emphasizes that Brazilian rules do not stimulate investment for such purpose and this can degrade those resources. In the past, the electrical worldwide systems used to have a centralized public utility which could include the several costs of ancillary services for electric power supply in the final price of the active power. After the privatization and decentralization, there was the need to separate the remuneration for such ancillary services. The resolutions that rule the reactive power ancillary services of synchronous generators have developed differently in several world regions. In this work it is given a description of some foreign legislations, which are then compared to the present status of Brazilian legislation, indicating its questionable aspects. Indexes are proposed for the selection of generators to supply reactive power to some electric power system area. It is proposed the public bidding for this supply taking the indexes into account, so that the price will depend on the effective contribution of each generator to the voltage rise in the target area. Simulations are presented to illustrate that the generator choice depends upon its localization. The need of reactive power support to improve the security margin against voltage collapse can be indicated by several indexes. It is shown a top view of the voltage collapse proximity indicators, with emphasis to those selected for this work. Often the electric power system operators call for a reactive power redispatch for voltage profile correction, but it is shown that sometimes this procedure leads to a risk of voltage collapse The dynamical behavior of synchronous generator excitation systems is very important for the reactive power dispatch. The operator requirements from Brazil, USA and Canada are presented. It is proposed a technique for voltage regulator adjustment, taking into account the time constant, the regulation error and the ceiling voltage, with illustration by means of simulations. Concluding, several suggestions are synthesized towards the evolution of the legislation concerning to reactive power supply from synchronous generators.