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Power flow results of SMIB in PSS/E do not match the hand calculations

asked 2020-08-22 14:47:00 -0500

cresg gravatar image

updated 2020-08-22 14:50:01 -0500

I modeled a single machine infinite bus (SMIB) network with the following data:

Sb = 100 MVA; f = 60 Hz; P = 1 pu; Pf = 0.95; Xl1 = j0.2 pu (transmission line 1 reactance); Xl2 = jo.3 pu (transmission line 2 reactance); Generator X'd = 0.3 pu;

I added two buses, two lines and two generators. Bus 1 consisted of generator whose Pgen was set to 1 MW, Qmax=Qmin was set to 0.328 Mvar based on pf=0.95, and X Source set to 0.3. To model an infinite bus, I set the type code of bus 2 to 3 (swing) with generator X Source (pu) set to 99999. For transmission lines, pu reactances were added as Line X (pu).

I was interested in the bus 1 Voltage (pu) and Angle (degree). The results I got in PSS/E were: Voltage (pu) = 1.0004 Angle (degree) = 0.07

However, the results I got by hand calculations were different: Voltage (pu) = 1.213 Angle (degree) = 20.25

Where did I make the mistake?

  1. Did I model the infinite bus incorrectly?
  2. Did I add transient reactance X'd incorrectly?
  3. Or any other mistake?

Any help will be highly appreciated. Thanks.

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Try to set the infinite bus generator Xsource to a small value, say 0.1 p.u.

ffl gravatar imageffl ( 2020-08-22 23:17:38 -0500 )edit

Tried Xsource=0.1. It doesn't make any difference.

cresg gravatar imagecresg ( 2020-08-23 02:58:00 -0500 )edit

Can you show your hand calculations?

ffl gravatar imageffl ( 2020-08-24 23:21:33 -0500 )edit

I checked the hand calculations and they turned out to be wrong. I did the calculations again, and now the results are in line with the PSS/E output.

cresg gravatar imagecresg ( 2020-08-25 01:18:56 -0500 )edit

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answered 2020-08-24 02:09:05 -0500

perolofl gravatar image
  1. Xsource must be low for an infinite bus, as ffl wrote. But, Zsource is not used in load flow so it doesn't affect the steady state voltage.
  2. Transient reactance is only applicable in dynamics, not in load flow.
  3. The hand calculation is wrong, because the PSSE results are correct.
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1. Verified. Zsource has no effect on the steady-state voltages. 2. Will the machine's Xsource have any effect on the dynamics if I use GENCLS model? 3. I checked the hand calculation again. It was wrong. Thanks for pointing out.

cresg gravatar imagecresg ( 2020-08-25 01:13:00 -0500 )edit

2. Yes, it is the reactance of the machine.

perolofl gravatar imageperolofl ( 2020-08-25 03:43:38 -0500 )edit

Thank you.

cresg gravatar imagecresg ( 2020-08-25 03:55:13 -0500 )edit

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Asked: 2020-08-22 14:47:00 -0500

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Last updated: Aug 24