sir in this attachment please find the question 12 and 13. i'm unable to understand how the answer has been derived. if any one can help me, i'm thanking them in advance
Attachments

66.3 KB Views: 41
12) Is a twophase generator.. You should know that the phase will be 90 degrees out of phase, so you plot both 70Vrms signals as vectors. One is at 0degrees, the other at 90degrees. Then, you draw them head to tail, then draw a new vector from the origin. Do the trig, it works out to be 90Vrms.
sir considering phase vectors one at 0 degrees and another at 90 degrees, it becomes pythagorous formula.
just by going the values rather than it is rms or avg √(70^2+ 70^2) =√(4900+4900) = √(9800)
again i'm somewhere wrong, please help out
Your answer agrees with the answer in your pdf file. What's the problem?12) Is a twophase generator.. You should know that the phase will be 90 degrees out of phase, so you plot both 70Vrms signals as vectors. One is at 0degrees, the other at 90degrees. Then, you draw them head to tail, then draw a new vector from the origin. Do the trig, it works out to be 90Vrms.
sir considering phase vectors one at 0 degrees and another at 90 degrees, it becomes pythagorous formula.
just by going the values rather than it is rms or avg √(70^2+ 70^2) =√(4900+4900) = √(9800)
again i'm somewhere wrong, please help out
√9800≈99, not 90. 99 is the answer in his problem sheet.He just rounded up to 90Vrms. If you input RMS into the trig, then you will return RMS.
Steve
I'm glad you said that. I thought I was going nuts.Am I bad? That was a strange thing, I saw 98.994 and rounded down to 90
Steve
sir thank you. i too have not noticed answer before asking you reply. i thank ron H sir also for his valuable suggestion.12) Is a twophase generator.. You should know that the phase will be 90 degrees out of phase, so you plot both 70Vrms signals as vectors. One is at 0degrees, the other at 90degrees. Then, you draw them head to tail, then draw a new vector from the origin. Do the trig, it works out to be 90Vrms.
13) Same idea as 12, except the angle is now smaller.
Steve
sir thank you, with this i got the funda of this question. sir i think if there are more no. of pole pairs, then the spacing between the phases will be by the formula 360/(n*2). if any thing wrong, please diect meQuestion 13 asks "how much voltage would be measured between any two open wires?"
So, there are 3 pole pairs, thus 360/(3*2) spacing between phases, or 60 degrees. Use trig. to solve for the resultant vector.
Steve
sir i really thank you. it gave me a very good idea about this.Both of these questions are intended to test knowledge of polyphase systems. Both are essentially asking:
"what is the line voltage of a N phase system, given that the phase voltage."
question 12 is a N=2 phase system so
Vline=Vphase*sqrt(2)=70*sqrt(2)=98.99
question 13 is a N=3 phase Wye so:
Vline = Vphase*sqrt(3)=70*sqrt(3)=121.24