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1. This question is for finding the condition where system stability is maintained after the fault. From equal angle criteria, for stability of system: area C = area B. Since network restores at 80deg and the power equations are not given we assume this as critical clearing angle. "Critical clearing angle states that If the fault is cleared before critical clearing angle (here 80deg), stability is maintained." So for fault clearing angle less that 80 deg; area C will be less than area B and still stability is maintained. Hence the condition is : area c <= area B; conversely area B>=area C. If this may help you.
2. can you try with wildi method as well plz.
3. From Wildi equation 15.8: For max power/torque; R2/S=IZ1I where R2= 0.3 Z1= r1+jx = 0.2+j(0.25+0.35) = 0.2+j0.6 = 0.632<71.6 deg Therfore, S=R2/IZ1I = 0.3/0.632 = 0.475
4. You can find hand written pdf solution 3rd edition somewhere in the internet.
5. @LyceeFruit @tpkjr2006 Thank you for your kind suggestion. I do have the 2017 version as well.
6. I am 32 Passed FE 1st try Jan 2018 ( from JPN) Failed PE 1st try Oct 2018 PE 2nd try target on Oct 2019
7. Still waiting for someone to response on this.
8. Thank you Zach for the attachment, and happy to say that is what i followed. I believe Open wye must be the same approach like open delta that you have mentioned. I wonder if some one agree with my above answers so that i can know i am in right track .
9. My understanding may be incorrect but i see the 460.9 statement as following: "When a capacitor is connected on the load side of the motor overload device, line current will be reduced due to an improved power factor, which must be taken into account when selecting the rating of a motor overload device. But this effect of capacitor mentioned above shall not be considered while determining the motor circuit conductor rating. This is for determining motor overload device only. "
10. If no other adjustments or correction factors are given use 75degC. You can see in NEC'17_Annex D Example D7 doing the same .
11. I tried to solve Graffeo Ex38 by Wilid method but i got different answers than one in the Graffeo. I think i am missing something with my calculation. Please let me know who have done this problem with Wildi method. For those who don't know the question: "A 120V, 6OHz, 6 pole, delta connected, three phase induction motor has the following characteristics. At standstill: Z stator = 0.2+j 0.25 ohm; Z rotor = 0.3+j 0.35 ohm. Find Pmax. The slip at which Pmax occurs and the Torque N- m at that point." Book ans: Pmax= 16.88 KW; Slip=0.278; Torque=186.05 N-m My ans: Pmax=8.687 KW; Slip=0.476; Torque=69 N-m
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