Case study 1

The effect on voltage stability of load behavior  and reactive power compensation from a static point of view is analyzed.  The study is performed with an equivalent electric system that feeds, through a LCT transformer,  an induction motor and a  thermostatic load. Using different load models  the characteristic  reactive power - voltage (Q-V) is obtained before and after a short circuit. The results demonstrate that voltage stability is strongly dependent of  load characteristic and  the action times of the reactive compensation control system.

Fig. 1.- Study network for case 1

    The voltage stability problem at the network of Fig. 1 can be detected performing a cuasi-static analysis based on V-Q curve, as shown in Fig. 2. For this purpose, the system dynamic behaviour is evaluated considering different operation characteristics for the network elements (cases 1 to 5) before and after the outage of one of the lines, as a consequence of the clearance of  a three-phase fault that occurs in the middle of one of them. In cases 3 and 4, as depicted in Fig. 2, the system is close to a critical situation, since the voltage profiles are very reduced and even curves do not intersect (collapse), in any of these cases control actions must be taken to ensure the system operation in acceptable  voltages levels.

Problem Solution :

Fig. 2.- Voltage stability cuasi-static analysis for the network of Fig. 1

Theoretical details:

The full theoretical details of the proposed solution are free available in a pdf file

Software developed :

The free available Matlab program was implemented to solve the problem