Power Protection

(See attached file for full problem description)

Power Systems problem 8

Attached is a question that I missed. My answer is D Vsourceold =.9167 Then we solve: VSourcenew=Vsourceold*480/460= .9167*480/460=.95655 I just posted 3.10. I could not enter all the text but here is what is missing On the bottom diagram for Zone 1 Vbase1=240 volts Zbase 1=(240^2)/30,000=1.92 Ohms Sbase=30kVA On the bottom diagram for Zone 2 Vbase2=480 volts Zbase2=(480^2)/30,000=7.68Ohms On the bottom diagram for Zone 3 Vbase3=120 volts Zbase3=(120^2)/30,000=.48 Ohms Ibase3=30,000/120=250A

Power Systems problem 9

This is a question that I got the wrong answer on. I wanted to know what was the correct answer and how it is derived. The answer I chose was B Take Vsp.u.=.95655 from problem eight. Also, from problem seven, Xt1p.u.=0.0726 Xlinep.u.=0.189 Xt2p.u.=0.1 Zloadp.u.=1.36+j0.3 Iload p.u.=Isp.u.=Vsp.u/j[(Xt1p.u.+Xlinep.u+Xt2p.u.)+Zloadp.u.]= 0.95655(angle)0 degrees/[j(0.1+0.189+0.0726)+1.36+j0.3]= 0.95655/(j0.3616+1.36+j0.3)= .9565/(1.36+j0.6616)= 0.9565/1.5124(angle)25.94 degrees= 0.63243 (angle)-26 degrees Iload=Iloadp.u.*Ibase3= Ibase3=Sbase3/Vbaseln=20000/(115/sqrt3)=301

Power Systems problem 14

Attached is a question in which I cannot find an answer. I have what I believe is the correct answer to the question but it does not derrive any possible answer for this multiple choice question. Please let me know what is the correct answer and how it is derrived. I used the formula: P1=V1*[Y11*V1*COS(-sigma11)+Y12*V2*COS(Delta1-Delta2-Sigma12)+Y13*V3*COS(Delta1-Delta3-Sigma13)] so that P1=1*[11.18*1*COS(63.43)+4.47*1.1*COS(0-16.97-116.57)+6.71*.9342COS(0-21-116.57)]=5-3.38713-4.62678=-3.0139

Power Systems problem 15

I could not find any of the available answers. Please check my work. Refer to the attached document. Please let me know the correct answer and how it is derrived. We will take V=4000 V X=3 Ohm R=1 Ohm omega=2*pi*60rad/sec X=jX+j1/(X*2*pi*60)+j(X*2*pi*60) Z=R+j[X-1/(X*2*pi*60)-[1-1/(2*pi*60)-(1*2*pi*30)/100] Z=1+j[3-1/(3*2*pi*60)-(1-1/(2pi*60)-(1*2*pi*60/100)] =1+j(-1.76808)=2.0313angle-60.51 degrees so 4000/2.0313=1969 does not come to any of the answers