Introduction to Electric Circuits

200 Transient analysis

Solution

Figure 8.37

V:,kV(

R C

? HI

-Os~

Th~

R C

Th2

) L

The circuit is shown in Fig. 8.37 and it should be noted that the thyristors Thl
and Th2 may be considered to be simply switches which are either closed (when
they are turned on) or open (before they are turned on).
At the instant of closing the switch the current in the circuit is zero and the
1 kV is shared equally between the capacitors. When thyristor Th I turns on it
short circuits the RC circuit in parallel with it and the circuit will then be as
shown in Fig. 8.38, the R and the C being those in parallel with the still open
switch Th2. The transform circuit takes the form shown in Fig. 8.39.

lkV(

_~ R C

:) L

Figure 8.38

.~ R 1/Cs

I I 1

500

s

@

1000 (~

s ) I3

Ls

Figure 8.39

From the transform circuit we have that

i(s) - [(lO00/s)- (500/s)]/(R + 1/Cs + Ls)

= 500/~(R + 1/C~ + L~)

= 500/Ls 2 + Rs + 1/c

= (500/L)/[s 2 + (R/L)s + 1/CL]