Study On The Influence Of OLTC On Power System Static Voltage Stability

In recent years, several large-scale voltage collapse incidents due to on-load regulating transformator (OLTC) happened in succession throughout the world,which arouses widespread concern about the influence of OLTC on power system voltage stability. Based on this, the influence of OLTC on static voltage stability is analyzed in this paper. Firstly, this article studies the influence of OLTC transformer ratio change on static voltage stability by using the ternary analytical method of voltage U, power P and load impedance angleφ. On the basis of the equivalent circuit, the formulas of load node maximum power and pull-in voltage are deduced; in the space of U -φand P -φ, variation characteristics of the critical voltage curve U cr-φand the maximum transmission power curve Pm ax-φbetween the pre-and post adjustment of the OLTC transformer ratio are discussed, and the effect of OLTC adjustment on the maximum transmission power and critical voltage is studied; using the features, the effect on operating range of voltage stability between the pre-and post OLTC adjustment is analyzed; based on system's current operation state, two critical variable ratio indexes of on-load regulating transformer are obtained, which are respectively corresponding to pull-in voltage and the maximum transmission power. Secondly, considering the case of power system connected distributed generation, the influence of OLTC adjustment on static voltage stability adjustment is researched by using the methods of P-U and Q-U curves and method of ternary analytical. Based on the system with OLTC and DG, taking load node and OLTC secondary side as the research objects, variation characteristics of P-U and Q-U combined with U cr-φand Pm ax-φbetween the pre-and post transformer ratio adjustment by using P-U and Q-U curves combined with the ternary analytical method are studied, so that the effect of system with DG caused by adjustment of transformer ratio is explored. Finally, the mechanism of voltage instability caused by the change of OLTC transformer ratio is explained by using the ternary analytical method in the space of U -φand P -φ.