Research Of The Effect Of On-load Tap Changer Transformer And Control Strategy On The Power System Voltage Stability

The rapid development of global economy has lead to the sustained growth of electricity demand, and the power system scale is rising at the same time, so these all bring many challenges for the secure and stable operation of power system. Voltage stability is an important part of the stability studies in power system, and now it has increasingly become the focus of international and domestic scholars. OLTC is an essential equipment of regulating voltage in power system, and during the running processes, it can achieve the goal of regulating voltage and reducing losses by automatically adjusting the taps and changing the transformation ratio, so it has been widely applied in the power system.This thesis first described the research status of the effect of OLTC on the power system voltage stability, introduced the model of OLTC, composite load and generator respectively, and then established the system model according to the different system structures, which has laid the foundation of analyses and researches.Taking the single machine infinite bus system as the objective, the nonlinear bifurcation theory and the software as the simulation tool, this thesis analyzed the effect of OLTC’s various factors on the voltage stability. Then setting the system’s operating point at the critical stable point and taking the varying situations of voltage at load side as the criterion, the effect of OLTC was explained through the comparison for the steady state of system voltage with and without OLTC. Then the control strategy of OLTC and the effect of locking, time delay and equivalent reactance on the system voltage stability were discussed, and the conclusion was obtained that the dynamic regulation of OLTC can restrain the voltage collapse of load bus to a certain extent.Then the regulation and control strategies of OLTC were researched. The linear state feedback control was introduced in the power system with OLTC, which can delay the system voltage stability point, enlarge the stability region, and sequentially enhance the system voltage stability. Finally, combining the adjustment of OLTC and the switch of the reactive power compensator, the aim of improving the power system voltage level and decreasing the power loss of the system can be significantly achieved by the reasonable regulation and control.