Effects of H.V.D.C. transmission line on the transient performance of an A.C. power system : a digital computer study

Abstract

The aim of this work is a comparative study of the electromechanical transient phenomena and of the stability limits of synchronous power systems, when they are mainly interconnected by a. c. transmission lines, but when one of the a. c. lines is replaced by the d.c. one. A thorough survey of the recent literature on h. v. d. c. technology has been made in order to be conversant with latest developments in the field. Digital computation and numerical analysis are used to study mathematical models of the systems under consideration. For the h. v. d. c. system, three digital programmes have been established to find the characteristics of the converter, to simulate the h.v.d.c. link in the a. c. power system and to study the transient behaviour of the systems, respectively. For the a. c. system the Park's equations describing the behaviour. of the synchronous machines are modified to suit the digital computers Then two digital programmes have been written, for the a. c. system one to draw the swing curves and the other to find the stability boundaries which incorporate the A. V. P. and the speed governor. To make a comparative study of the a.c. - d. c. system and of the equivalent a.c. system, two new comprehensive programmes have been established by incorporating the d.c. programme for the transient studied in the modified a.c. programmes. One of the digital programmes draws the swing curves while the other finds the stability boundaries of both the systems, with or without A. V. R. Thus, by performing different tests, it has been established that from the stability point of view the a. c. -d. c. system can be made superior to the equivalent a. c. one, provided that provision is made for increasing the power through the d. c. line when a fault is sensed.