The Number of Chained pi-type circuits for Dynamic Analogy of Half-wavelength Transmission Line Considering Short-circuit Fault

The physical analogy is one of the key technologies to study the characteristics of half-wavelength transmission line. Dynamic model test is the main technical means of physical analogy. In general, the equivalent lumped-circuits consisting of some chained pi-type circuits or T-type circuits are used to analogy transmission line, and the number of the chained circuits is the most key parameter to to establish dynamic test of transmission line. In this paper, firstly, a rigorous derivation of a pi-type circuit analogized by the method of order parameter equivalence is carried out. Then, the simulation of the half-wavelength transmission line with different number of the chained circuits is carried out from the transient characteristics. Finally, the voltage changes at each observation point after the short-circuit fault are analyzed and compared. It is shown that when the short-circuit point is close to the middle of the line, the required number of the chained circuits will be less, while the short-circuit point is near the end of the line, the required number of the chained circuits will be more. When the short-circuit fault occurs in the middle of the line, 10 chained pi-type circuits can establish good equivalence between the lumped-circuits and the 3000km transmission line; When the short- circuit fault occurs near the end of the line, increasing the chained number to 37 is enough; When the short-circuit fault occurs in other parts of the line, it is enough to use 17 chained pi-type circuits to equivalent the 3000km transmission line. Considering the uncertainty of the location of the short-circuit fault, it is enough to use 37 chained pi-type circuits to equivalent the half-wavelength transmission line. Considering the uncertainty of the location of the short-circuit fault, it is enough to use 37 chained pi-type circuits to equivalent the half-wavelength transmission line. These works are instructive for the physical analogy of HWACT lines.