Power Quality Curve Questions - from Shorebrook PE Exam Q. 10

Hi guys,

I have a few questions regarding power quality curves, since I haven't seen this all that much in practice PE exams except for the Shorebrook PE Power exam.

In the attached given problem, I understand that given the current lagging 0.8 power factor curve, power cannot be transmitted or changed/increased from PA to PB, since PB is outside of the 0.8 p.f. curve.

My questions are:

1. This would mean that the power factor would have to change to pf = 0.95 lag to get to the new PB power point, correct? (Sounds like a silly question, but I just want to make sure I understand this right.)

2. The voltage would also have to change to align with the pf = 0.95 curve, correct? If I remember correctly, above the dashed curve line is the stable (desired) region of operation and below the dashed line is the unstable (undesired) region of operation.

Anything else I should know about power quality curves like these?

Thank you for any help on this topic!

(I also have more questions from the Shorebrook PE Power Exam that I will post in separate topics.)

akyip said:

1. This would mean that the power factor would have to change to pf = 0.95 lag to get to the new PB power point, correct? (Sounds like a silly question, but I just want to make sure I understand this right.)

2. The voltage would also have to change to align with the pf = 0.95 curve, correct? If I remember correctly, above the dashed curve line is the stable (desired) region of operation and below the dashed line is the unstable (undesired) region of operation.

Click to expand...

P-V curves are conceptual analyses of power systems. They tell you the voltage stability of your system at different operating points. So if your system is operating at 0.95 PF with load PB, then yes the voltage would be higher. This graph doesn't tell us how we need to change the voltage, rather it tells us what happens to voltage as other parameters are changed. The dashed line in the diagram is running through the nose point of all the graphs. This is the point at which voltage loses stability. Below this point the system will have low voltage and be drawing much more current. That will eventually lead to voltage collapse, generator phase angle increase, generator acceleration, and eventual 0MW power transmission.