Hi
@yaoyaodes,
I'll do my best to answer your questions:
The maximum power formula comes from the real power transformer formula:
Pmax = (|E1|•|E2| / X) sin(δ)
Where δ is the angle between the two voltages E1 and E2
The maximum value of sin(δ) is sin(90º) = 1.
An angle of anything other than δ = 90 degrees results in a value of sin(90º) < 1, which decreases the amount of power transformer.
Therefore, the maximum amount of power occurs when the electrical torque angle (how far the rotor leads the stator poles by) is equal to δ = 90º, and the resulting maximum power is calculated by:
Pmax = (|E1|•|E2| / X) sin(90º)
Pmax = (|E1|•|E2| / X)•(1)
Pmax = (|E1|•|E2| / X)
This formula calculates the amount of real power in watts transferred from the leading voltage source to the lagging voltage source, in this case from VA (the generator on the left) to VB (the generator on the right).
I = 8,165A<45º is the amount of line current from generator A on the left to generator B on the right.
Using the power formula S1ø = |I|²Z, we can calculate the amount of
single-phase power absorbed in the line. Since the line is purely reactive (Z = 0 + j50Ω), the power will be
reactive power (S1ø = 0 +jQ1ø) in
VARs:
S1ø = |I|²•Z
Q1ø = |I|²•X
Q1ø = |8,165A|²•(50Ω)
Q1ø = 3,333.4 MVAR
This is the amount of
single-phase reactive power absorbed in just one out of the three (XL = 50Ω) line conductors since it is a three-phase system.
To calculate the total
three-phase reactive power absorbed in the entire three-phase system, we have to account for not just one of the line conductors but by all three. We can do this by multiplying single-phase power by three (3):
Q3ø = 3•Q1ø
Q3ø = 3(3,333.4 MVAR)
Q3ø = 10,000 MVAR
The total amount of reactive power losses in the transmission line is approximately 10,000 MVAR.
If you are looking for more help, these are the types of topics we explore in much more depth in our online class for the new CBT format of the PE exam. You can sign up today for the Free Trial by clicking on the button in my signature below, or by visiting
www.electricalpereview.com.