initial commit / add all books

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diff --git a/1938/CH6/EX6.20/6_20.jpg b/1938/CH6/EX6.20/6_20.jpg
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diff --git a/1938/CH6/EX6.20/6_20.sce b/1938/CH6/EX6.20/6_20.sce
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+clc,clear

+printf('Example 6.20\n\n')

+

+Power_total=1.414 //per unit

+V_L=1 //per unit

+phi_t=acos(0.707)

+I_L_T=Power_total/(sqrt(3)*V_L*cos(phi_t))  //Total current

+//Current supplied by each alternator

+I_1=I_L_T/2

+I_2=I_1

+V_ph=V_L/sqrt(3)

+

+phi=acos(0.707)

+R_a=0,X_s=0.6 //resistacne and synchronous reactance

+E_ph=sqrt(  (V_ph*cos(phi)+ I_1*R_a)^2 + (V_ph*sin(phi)+I_1*X_s)^2          )

+delta= atan((I_1*X_s+V_ph*sin(phi)) / (V_ph*cos(phi))) - phi    //power angle

+

+printf('EMF is %.4f p.u. and power angle is %.2f degrees ',E_ph,delta*(180/%pi))

+printf('\n\nFollowing assumptions were made :\n')

+printf('1.Terminal or bus bar voltage at ppoint of connection is constant\n')

+printf('2.The alternators are identical and are initially equally excited\n')

+printf('3.The power supplied by prime movers is adjusted so that each machine carries half the load represented by external impedance Z=R+ j 2pifL , where R and L are constant\n')

+printf('4.The stator resistance is negligible')