1 2 function [r]=mag(A) 3 x =real( A ) 4 y =imag( A ) 5 r =sqrt(x^2+y^2) 6 endfunction 7 8 j=%i 9 // considering co i ls to be star co nn ec te d 10 Vl=400 // line volta ge 11 Vph=Vl/ sqrt(3) 12 Rph=15 // resistance of lo ad
13 Xl=2*%pi*50*.03 // induct ive rea ctan ce of e ac h coi l 14 Zph=Rph+Xl*j
15 Iph=Vph/mag(Zph) 16 Il=Iph
17 pf=Rph/mag(Zph) //p ow er fac tor 18 P =sqrt(3)*Vl*Il*pf
19 mprintf (”I n star co nn e ct ed circuit , \ nP ha se curren t=
%f A, \ nLine cur ren t=%f A, \ nPo wer ab so rbe d=%f k W \ n ”, Ip h, Il,P/10 ^3 )
20 // considering co i ls to be delta co nn ec te d 21 Vph=Vl
22 Iph=Vph/mag(Zph) 23 Il =sqrt (3)*Iph 24 P =sqrt(3)*Vl*Il*pf
25 mprintf (”In delta co nn ec te d circuit , \ nP ha se curren t=
%f A, \ nLine cur ren t=%f A, \ nPo wer ab so rbe d=%f k W \ n ”, Ip h, Il,P/10 ^3 )
26 // an sw er s va ry from th e te xt boo k due to rou nd off error
Scilab code Exa 9.2 Example on Three Phase Circuits
1
2 // calculat ing ph as e cur ren t 3 Vl=440 // line volta ge
4 Vph=Vl
5 Pout=200D+3 //output 6 e=.91 // eff ici enc y 7 Pin=Pout/e // in put 8 pf=.86 //p ow er fac tor 9 Iph=Pin/(3*Vph*pf)
10 mprintf (” Curre nt dr aw n by each mo to r phase =%f A \n ”,
Iph)
11 // calculating line cu rr en t 12 Il =sqrt (3)*Iph
13 mprintf (”Line curre nt= %f A \ n”, Il)
14 // calculat ing active and reactive co m p o n en ts of ph ase current
15 phi= acos(pf) 16 Iact=Iph*pf
17 Ireact=Iph* sin(phi)
18 mprintf (” Active co mp on en t of phas e curren t=%f A \
nReactive co mp on en t of pha se curren t=%f A ” ,Iact,
Scilab code Exa 9.3 Example on Three Phase Circuits
1
2 Vl=400 // line volta ge across alternator and motor 3 Vph=Vl //as th e motor is delta co nn ec te d
4 Pout=112D+3 //out pu t of mo tor 5 e=.88 // eff ici enc y of motor 6 Pin=Pout/e // input to mo to r 7 pf=.86
8 phi= acos(pf)
9 Il=Pin/( sqrt (3)*Vl*pf) 10 Iph=Il/ sqrt(3)
11 mprintf (”Curre nt in eac h mo to r ph as e , Ip h=%f A \ n”,
Iph)
12 // alternator is star co nn ec te d
13 mprintf (”Cur re nt in ea ch alter nator ph as e=%f A \ n”, Il
)
14 // calculat ing active and reactive co m p o n en ts of cur ren t in e ac h ph as e of motor
15 Iact=Iph*pf
16 Ireact=Iph* sin(phi)
17 mprintf (”Acti ve component of curren t in ea ch ph as e
of motor =%f A \ nRe acti ve com po nen t of current in
each phase of mo to r=%f A \ n”, Ia ct,Ire ac t)
18 //ph as e angle be tw een th e ph as e voltage and ph as e cur ren t will be th e same for b o t h motor and alternator i f we neglect line i m p ed an ce 19 Iph=Il
20 Iact=Iph*pf
21 Ireact=Iph* sin(phi)
22 mprintf (”Acti ve component of curren t in ea ch ph as e
of alter nator= %f A \ nRe acti ve com po nen t of current
in e ac h ph as e of alternator= %f A \n ”, Ia ct, Irea ct
23 //T he ans we rs va ry fro m the text book due to ro un d off er ro r
Scilab code Exa 9.4 Example on Three Phase Circuits
1
2 function [z]=pol2rect(r,theta)
3 x=r* cos(theta*%pi/180) 4 y=r* sin(theta*%pi/180) 5 z=x+y*%i 6 endfunction 7 function [r]=mag(A) 8 x =real( A ) 9 y =imag( A ) 10 r =sqrt(x^2+y^2) 11 endfunction 12
13 // calculating cur re nt in e a c h line 14 Vl=400 // line volta ge
15 Vph=Vl/ sqrt(3)//pha se voltage 16 Ir=8D+3/Vph
17 Iy=6D+3/Vph 18 Ib=4D+3/Vph
19 mprintf (”Cur re nt in R −phase , I r=%f A \ nC ur re nt in Y −
phas e , Iy= %f A \ nC ur re nt in B −phas e , Ib= %f A \n ”,Ir,
Iy,Ib)
20 //Loa ds on thr ee phases are r e s i s t i v e 21 Ir=pol2rect(Ir,0)
22 Iy=pol2rect(Iy,-120) 23 Ib=pol2rect(Ib,-240) 24 In=Ir+Iy+Ib
Scilab code Exa 9.5 Example on Three Phase Circuits
1
2 Pout=30D+3 //output 3 e=.86 // eff ici enc y 4 Pin=Pout/e // in put 5 Vl=440 // line volta ge 6 pf=.83 //p ow er fac tor 7 Il=Pin/( sqrt (3)*Vl*pf)
8 mprintf (”Line curre nt= %f A \ n”, Il)
9 Iph=Il/ sqrt(3)//mo tor is delta con ne ct ed
10 mprintf (”Phase cu rr en t=%f A”, Iph )
Scilab code Exa 9.6 Example on Three Phase Circuits
1 2 function [r,theta]=rect2pol(A) 3 x =real( A ) 4 y =imag( A ) 5 r =sqrt(x^2+y^2) 6 theta=atand(y/x) 7 endfunction 8 function [z]=pol2rect(r,theta) 9 x=r* cos(theta*%pi/180) 10 y=r* sin(theta*%pi/180) 11 z=x+y*%i 12 endfunction 13 function [r]=mag(A) 14 x =real( A ) 15 y =imag( A ) 16 r =sqrt(x^2+y^2) 17 endfunction 18 j=%i
19 // calc ulat ing ph as e curr ents − le t the sequ ence be RYB 20 Vl=440 // line volta ge
21 Vph=Vl // delta conn ect ed load
22 Zph1=150 //im pe da nc e of the ph ase be tw ee n A an d B( r e s i s t i v e )
23 I1=Vph/Zph1
24 mprintf (” I1 =%f A at 0 degree s w. r . t . Vry \n ”, I1)
25 Zph2=30+50*j //imp ed an ce of the ph as e be tw ee n B and C 26 I2=Vph/mag(Zph2)
27 / /a s t h e lo ad is in du ct iv e , cu rr en t will la g t h e voltage Vyb by phi 2
28 phi2=atand(50/30)
29 mprintf (”I2=%f A at −%f deg ree s w. r . t . Vyb \n ”, I2,
phi2) 30 C=20D-6 31 f=50 32 Xc=-(1/(2*%pi*f*C))*j 33 I3=Vph/mag(Xc) 34 / /a s t h e lo ad is ca pa ci ti ve , cu rr en t will le ad t h e voltage Vbr by 90 degree s
35 mprintf (” I3 =%f A at 90 degree s w. r . t . Vbr \ n”, I3)
36 37 // calculating line cu rr en ts − 38 Vry=pol2rect(440,0) 39 Vyb=pol2rect(440,-120) 40 Vbr=pol2rect(440,-240) 41 I1=Vry/Zph1 42 I2=Vyb/Zph2 43 I3=Vbr/Xc 44 // us in g KCL 45 Ir=I1-I3 46 Iy=I2-I1 47 Ib=I3-I2
48 mprintf (”Cur re nt in lin e R, Ir= %f A, \ nCu rre nt in
li ne Y, Iy =%f A , \ nC ur re nt in li ne B, Ib =%f A , \ n ”,
Scilab code Exa 9.7 Example on Three Phase Circuits
1
2 Vl=1100 // line volt age
3 Vph=Vl/ sqrt(3)// star conn ect ed load 4 Il=80 // current th rou gh load
5 Iph=Il 6 Zph=Vph/Iph
7 P=100D+3 //pow er dr aw n by load 8 pf=P/( sqrt(3)*Vl*Il) //p ow er fac tor 9 Rph=Zph*pf
10 Xc =sqrt(Zph^2-Rph^2) 11 f=50
12 C=1/(2*%pi*f*Xc)
13 mprintf (” Capacitance per phase =%f mi cr oF” , C*10 ^6 )
14 //A nswer va ry fro m the text book due to ro un d of f error