(*situace podle obrazku Obr. 34-V-4, skenovat0004.jpg *)

kV=1000;
μF=(10^(-6));
Unom=(22/(Sqrt[3]))kV;
U1=1.06*Unom;
f=50;
ω=2*Pi*f;
L1=0.05;
L2=0.1;
L3=0.1;
R2=100;
ser:=Plus@@#&;
par:=(((Plus@@((#)^(-1))))^(-1))&;
s:=Chop[Simplify[#]]&;
z1=I*ω*L1;
z2a=(1/(I*ω*c));
z2b=ser[{I*ω*L2,R2}];
z2c=ser[{I*ω*L3,Ro}];
z2=par[{z2a,z2b,z2c}];
U2[Ro_,c_]=U1*(z2/(z1+z2))//s;
Plot[{Abs[U2[200,c*(10^(-6))]],Abs[U2[250,c*(10^(-6))]],Abs[U2[150,c*(10^(-6))]],Unom},{c,0,10},PlotRange->All,AxesOrigin->{0,12000},PlotStyle->Thick,AxesLabel->{"c [μF]","U2 [V]"}]

(*Plot[{Abs[U2[200,c*(10^(-6))]],Abs[U2[250,c*(10^(-6))]],Abs[U2[150,c*(10^(-6))]],Unom},{c,0,1000},PlotRange->All,AxesOrigin->{0,12000},PlotStyle->Thick,AxesLabel->{"c [μF]","U2 [V]"}]*)

ClearAll[absI2]
absI2[Ro_,c_]=Abs[((U2[Ro,c])/z2c)];
najdiC[Ro_]:=c/.FindRoot[Abs[U2[Ro,c]]==Unom,{c,5*(10^(-6))}];
datIaC=Table[{absI2[Ro,najdiC[Ro]],najdiC[Ro]},{Ro,50,500}];
nahr=Interpolation[datIaC];
iMin=nahr[[1,1,1]];
iMax=nahr[[1,1,2]];

Plot[(10^6)nahr[i],{i,iMin,iMax},PlotStyle->Thick,AxesLabel->{"I [A]","c [μF]"},GridLines->Automatic]