Power system analysis, per unit system help

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The discussion focuses on a homework assignment involving power system analysis, specifically drawing a reactance diagram, calculating per unit impedances, and determining current at a specified voltage. One participant proposes that instead of using the per unit system, it may be more effective to work with actual quantities to ensure dimensional correctness in equations. They argue that while the per unit system can be useful for initial estimates, it can lead to confusion later on. The conversation emphasizes the importance of clarity in calculations and understanding the underlying principles of power systems. Overall, the thread highlights differing approaches to solving power system problems.
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Homework Statement


https://dl.dropboxusercontent.com/u/88040310/powerhw3.png
1. Draw the reactance diagram.
2. Calculate the per unit impedances
3. If bms #1 is operating at 30 kV, find the current
Assume base of 100 MVA, 300 kV on the generator side.

Homework Equations


P = VI
s = p +jq
Apparent power = (reactive power^2 + real power^2)^(1/2)

per phase equations, tap transformer equations

The Attempt at a Solution


Starting it slowly, is this how you draw the reactance diagram?
https://dl.dropboxusercontent.com/u/88040310/hw3xdiagram1.png
 
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At the risk of being called a heretic, I suggest that the best thing you can do is abandon the "per unit" system. Work with actual quantities, so that your equations make sense and are dimensionally correct. Per unit is useful only in that for certain system classes, it enables estimates of parameters before the actual values are know. Thereafter, it is simply a confusion factor (and a large one at that!).
 

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