Steady State Overvoltages of TCSC Terminals and Their Impact on Degree of Compensation and Transmitted Power of Radical Power System

Abstract

This paper studies, in a tutorial form, the impact of location of the TCSC on the degree of compensation and the transmitted power of a radial power system. The voltages of the two terminals of the TCSC have been examined at different locations with increase in the degree of compensation and transmitted power. The objective is to limit these voltages to 1.05 pu and obtaining maximum degree of compensation. Two cases were studied: (1) The case when the receiving end is a large AC system where the receiving end voltage is always maintained at 1.0 pu which is designated as case # 1 and (2) The case when the receiving end is an inductive load (R-L) load and it is designated as case # 2. For case #1, it has been found that sitting the TCSC at the sending or receiving end causes a large overvoltage. In contrast, sitting it at the midpoint could not cause overvoltage up to 0.5 degree of compensation. If it is higher than this value, overvoltage has been found. Thus placing the TCSC at the midpoint provides a compensation range up to 0.5. If the TCSC are disparted in two or three smaller TCSCs, which are equal in size and equally spaced along the transmission line, it has been found that higher degree of compensation can be obtained. This scheme has been found to be best compensation scheme to obtain a wide compensation range. In case 2, the sending end positioning has been found to cause overvoltage while the receiving end positioning provides a wide compensation range up to 1 without overvoltage at any point. Similar to case # 1, sitting the TCSC at the midpoint causes overvoltage at a degree of compensation greater than 0.5. For distributed TCSCs, a degree of compensation greater 0.5 can be obtained and the maximum degree of compensation depends upon the number of TCSCs. For case # 2, the best position has been found to be at the load end. In addition to the two study cases, a relation between the number of the distributed TCSCs and the maximum degree of compensation has been developed.