Star-connected, 3-phase, synchronous generator with armature resistance, reactance, leakage resistance. Calculate rated load and unity power factor

Thread Starter

Lambo Av

Joined Apr 24, 2019
59
If a 100 KVA star-connected 400 V three-phase, 60 Hz synchronous generator with armature resistance 0.35Ω/phase and 3.5Ω reactance and leakage resistance given is 1Ω/phase. Calculate at rated load and unity power factor at
i) No load e.m.f
ii) Internal e.m.f.
iii) percentage of regulation at full load

Where do I start from the question to fulfill the 3 questions?
 

Janis59

Joined Aug 21, 2017
1,183
School?? Where U broke?
400V is between phases, means phase to gnd being 400/sqrt3=230.94 V
PF=cos(fi)=0.35/(sqrt(0.35^2+3.5^2)=0.0995 (!!!! what is this the sh**???)
Then P=S*PF=100kVA*0.095=950 W of active power (somehow shamefully thin)
Then one phase contains 1/3 of power or 316.3 W what produces an Amperage 316.3/230.94=1.371 Amp of active component.
Wait wait, I miss here the leakage. It is only component summing to full load regime over the wires resistance, I misread instead those 3.5 Ohms. Actually, You cannot speak about armature resistance where is thought wires resistance, but try to not see it. Anyway, please correct my figures playing with 1 Ohm instead of 3.5 Ohm, so the figures will bit change. But why are given the no-load condition characteristic reactive Ohms - have no idea. Active R=0.35; reactive X(L)=1.0; Full Z=sqrt(0.35^2+1^2)=1.0595 absolute value of complex Ohms. Then Active current in each coil will be 230.94 V/0.35 Ohm; reactive 230.94 V/1 Amp and Full 230.94 V/1.0595 Amp. And PF=1.st divide to second (anyway an irrealistic figure).
 

Janis59

Joined Aug 21, 2017
1,183
Probably tutor with the strong aim was giving unrealistic figures, to test the student realizes each figure meaning. So, the PF value near to 1.0 is not a demand in theoretical tasks. The same as not all the figures are obligatorium need to be used into calculations. I am often giving th unneeded figures for my students. Them must understand by own that electrotechnical task have no use of figures about currency rate or virus mortality, or schoolhouse cornerstone weight.
 

Janis59

Joined Aug 21, 2017
1,183
PS EMF for motor will be Voltage minus current to active resistanvce, but in regime of generator it will be double as much smaller at the same rpm.
 
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