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//Book - Power system: Analysisi & Design 5th Edition
//Authors - J. Duncan Glover, Mulukutla S. Sarma, and Thomas J.Overbye
//Chapter-11 ;Example 11.7
//Scilab Version - 6.0.0; OS - Windows
clc;
clear;
function result=table(delcr) //Function to get result in table format using Euler’s method for diferent critical clearing angles
delta=0.4179 //Initial value of delta in rad taken from example 7.6
omega=2*%pi*60 //Initial value of omega in rad/s
H=3 //Value of H constant in pu-s
omegasyn=omega
t=0;
delt=0.02 //Step size
result=[]; //Initialization of result table
tc=0; //Initialization of critical clearing time
while t<0.861 //Maximum time for Eler's method is o.86
result=[result;t delta omega] //Updating the result table
ddeltat=omega-omegasyn //Calculation of ddeltat/dt using equation 11.4.7
deltab=delta+ddeltat*delt //Calculation of delta_bar using equation 11.4.9
if delta<delcr //Steps to calculate accelerating power for prefault condition
papu=1-0.9152*sin(delta)
pafb=1-0.9152*sin(deltab)
else //Steps to calculate accelerating power for postfault condition
tc=tc+1;
papu=1-2.1353*sin(delta)
pafb=1-2.1353*sin(deltab)
end
if tc==1 & delcr==1.95 //Displaying result of case 1(Stable) stable with Critical clearing angle of 1.95
printf('The critical clearing time for case 1 is %.2f sec\n',t)
elseif tc==1 & delcr==2.09 //Displaying result of case 2(Unstable) stable with Critical clearing angle of 2.09
printf('The critical clearing time for case 2 is %.2f sec\n',t)
end
domegat=papu*omegasyn*omegasyn/(2*H*omega) //Calculation of domegat/dt using equation 11.4.8
omegab=omega+domegat*delt //Calculation of omega_bar using equation 11.4.10
ddeltab=omegab-omegasyn //Calculation of ddelta_bar/dt using equation 11.4.11
domegab=pafb*omegasyn*omegasyn/(2*H*omegab) //Calculation of domega_bar/dt using equation 11.4.12
delta=delta+(ddeltat+ddeltab)*delt/2 //Calculation of delta for change in time using equation 11.4.13
omega=omega+(domegat+domegab)*delt/2 //Calculation of omega for change in time using equation 11.4.14
t=t+delt;
end
endfunction
case1=table(1.95) //case1 - critical clearing angle is 1.95 rad
case2=table(2.09) //case2 - critical clearing angle is 2.09 rad
printf(' ----------------------------- -----------------------------\n')
printf(' CASE-1 STABLE CASE-2 UNSTABLE \n')
printf(' ----------------------------- -----------------------------')
disp([case1 case2],'Time(s) Delta(rad) Omega(rad/s) Time(s) Delta(rad) Omega(rad/s)')
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