Voltage stability assessment by using local bus parameters

Keywords: Power systems, Voltage stability, Voltage stability limits Power systems are dynamic and multiparameter systems which are very complex. A modern electric power system is expected to be very well designed. The reasons of operating problems and faults in power systems are very diverse. Even if the power system in supply and demand balance, some operational or topological issues can couse stability problems. Power system stability generally refers to the capability of a power system to remain in a state of operation equilibrium under normal operation conditions and to regain an acceptable state of equilibrium after being subjected to disturbances. Stability problems are examined in different classes within the context of the occurrence and outcome mechanisms. Although power systems are designed properly in the beginning, sub-optimal hardware updates will be done by years as a result of continuous growth and industrialization. On the other hand, the variety and characteristics of the electrical loads are also changed by smart industrialization. New problems such as power delivery from distant and unexpected regions can occur as a result of power flow changes, increase in controlled loads and constant power loads, power system harmonics and reactive power demand increase. Renewable energy resources and distributed generations can cause unpredictable power flows and increasing complexity. As a result, the operating the power systems and maintening the quality have become increasingly complex. Many problems, which hypothetically predicted by engineers, began to become real from the 1980s. Increasingly complicated power systems can go under unexpected loading conditions and come on the edge of unstablity. Therefore, the studies for the stable operation of existing systems attract great interest for engineers. In this thesis, voltage stability assessment which is the one of the major stability issue in power systems are examined by using local bus measurements. Thevenin equivalent model behind the corresponding local bus are estimated and the critical parameters are calculated to define voltage stability limits of the bus. Verification of the approach was done on a simple power system by simulation. Then concepts were applied on IEEE 30 bus standart test system. The simulation results has shown that the proposed assessment approach has accurate enough to estimate voltage stability limits and suitable for real time applications.