# Static voltage stability investigations in power systems

The voltage instability and the voltage collapses became an undoubtedly important topic nowadays. Our electric power system needs to operate close to their stability limits due to the increased electric power demand, because the improvement of the system would be a very expensive alternative solution. Because of this fact it would be important for the operatorts to have precise and fast indicies to detect the closeness to system instability and indicate the dangerous operating state. Therefore, it is not surprising that we can find a lot of studies dealing with this topic. The topic of my thesis is to get to know the already exsisting methods from the literature, and to examine their effectivity using two test networks. One of the networks is a 39 bus IEEE test system. The other 40 bus system represents a real system because every parameter suits the real system’s properties. My examination expand to the viability and the complexity of this methods. In order to do this examinations I used the Power World and the PSS®E Xplore 34 network simulators, and I used MATLAB and Excel for data processing.

Reading the literature we can come across a lot of indicies, I only focused on the ones which are based on the actual state of the system. However, my thesis does not discuss indicites that are based on probability and estimations. The examined indicies are about using the actual voltage, current and power values of the system. In general, they can be optained by using load-flow calculations. When the indicies reach a defined value or come to a range, that means for the operators the closeness to the system instability in case of correct and precise calculations. So the system operators can act in time to prevent the voltage collapse.

Most of the examined indicators can be categorized as line stability indicies, they determine the stability by the loadability of power-lines. To calculate this values I used the PV analysis of the above mentioned simulator softwares. Using the PV module the voltage, current, and power values during different states of the system can be obtained.