This paper presents a new method to obtain a voltage stability index for unbalanced radial distribution system. Voltage stability index (VSI) is used only for balanced radial distribution system. By using the sequence component, the unbalanced in distribution system could be simplified into a single-phase system. From the positive and negative sequence value, the voltage stability index for unbalanced distribution system can be obtained easily. The IEEE 15 bus single phase test systems which is modified into three phase balanced system, and the Surabaya Utara 20 kV three-phase radial distribution system are used to verify the sequence based on Catastrophe theory VSI sequence method. The results show that voltage stability index ranking by using negative and positive sequences based on Catastrophe theory VSI is exactly the same with single-phase simulation. This method also has less execution time than the sequence based VRI and sequence based VSI methods.
- Direct ZBr power flow
- Sequence based VRI
- Sequence based VSI
- Sequence based catastrophe theory
- Unbalanced distribution system
- Voltage stability index