PPI Exam 2 #108

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ME->EE

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The solution to this question notes that "Since the source is ungrounded, the phase-to-phase voltage is the line voltage".



Does this mean that if there was a neutral you can't assume the phase-to-phase voltage is the line voltage?  I have been treating phase-to-phase voltage as line voltage for my entire time studying and haven't seen an issue yet.





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The solution to this question notes that "Since the source is ungrounded, the phase-to-phase voltage is the line voltage".



Does this mean that if there was a neutral you can't assume the phase-to-phase voltage is the line voltage?  I have been treating phase-to-phase voltage as line voltage for my entire time studying and haven't seen an issue yet.





8i5ZMP44_ZLWIu5ioeZYKy0BirLn_l7pBwP4Cja93J4o4OytlCD-lsxDqwNq0Lik3cEY8jrmzU29K-JwgIRdfqfacgoMfSomRMBVvAvmfKgW2aCjZS07LiP97gpKsDO9b-T5nkGe




PQEtHEH_AM2uOn5g5G6_6CU0oHm0U-PLqgu8_GWH4pG1g_sem6bjo4OSI2j0ujhSiySjgVh_qcQyE-E7AIuS1u7UnsiV0PPs888ocukx5ieCX23cDOHCEY7kQ1yhMwrKZ90rrk1p
For a Wye 3 phase-3 Wire system, Phase-to-Phase Voltage is equal to the Line voltage.  But Phase-to-Phase Voltage is never equal to sqrt of 3 time Phase Voltage.

 
I wouldn't read too much into the answer key on that one. Just by inspection, the voltage across the delta load connected to phases A & C is the phase-to-phase voltage of 12.5kV.

Does this mean that if there was a neutral you can't assume the phase-to-phase voltage is the line voltage?
Imagine if there was a neutral connected to ground, or point C on the load. Phase C on the source would be grounded on both sides, and that wouldn't work.

 
@BebeshKing so in general should I not assume that V phase = V Line /sqrt(3)? I should try to prove it each time?

Thank you both for the comments!

 
If I see a problem with Wye-3phase-3w system, I usually covert it to delta so that VL will be equal to Vphase. But for this problem, the configuration at the source does not matter weather it is a Wye or a Delta. 

 

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