Calculating Equivalent Series Resistance and Inductance for Parallel Branches

AI Thread Summary
To calculate the equivalent series resistance (Req) and inductance (Xeq) for two parallel branches, the correct method involves combining the complex impedances of each branch. The formula Zeq = (R1+jX1)*(R2+jX2)/((R1+jX1)+(R2+jX2) should be used to find the equivalent impedance, which can then be converted to polar form to extract the equivalent resistance and reactance. The simpler method of calculating Req and Xeq separately does not yield accurate results, as it overlooks the interaction between the resistances and reactances. It is crucial to ensure that calculations are done in the correct format, especially when dealing with per unit values. Using the combined approach will provide the correct equivalent values for the parallel branches.
Physicist3
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Hi,

If I have two brances, branch 1 and branch 2 which are in parallel and each branch has a resistance and inductance, to calculate the equivalent series resistance and inductance, can I calculate the resistance and inductance separately e.g.

Req = R1*R2/R1+R2 (and same for X),

or do I have to do it combined E.g.

Zeq = (R1+jX1)*(R2+jX2)/(R1+jX1)+(R2+jX2), and then convert to polar etc and back to rectangular to find the equivalent R and jX values? The two methods give me different answers?

Sorry, forgot to add, the values of R and X are in PER UNIT
 
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Physicist3 said:
The two methods give me different answers?
And the second one is correct. That should answer if the first one works.
Note that there are brackets missing.
 

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