PSS/E Dynamic Simulation - Negative accelerating P but frequency not decreasing

Wai
3 ●2 ●2 ●4

Hi Everyone,

I am trying to run a dynamic simulation under low load conditions with two generation units based on the PSSE sample case of SAVNW.SAV in the “EXAMPLE” directory. The contingency involves tripping a generator (the nuclear plant at Bus 101), leaving the whole system supplied by the remaining nuclear plant at Bus 102. The simulation run time is set to over 100 seconds.

From the output results, the total Pmech of all buses is always lower than the total Pelec of all buses, resulting in a negative total Paccl until the end of the simulation. As Paccl is negative all the time, I originally expected that the system frequency will keep decreasing during the simulation due to the generation deficiency in supplying the load. However, the system frequency drops to a certain level and then becomes flat as shown below.

"https:// http://www.dropbox.com/scl/fi/b2ua0uswlinktekck6iik/image001.png?rlkey=n53n82t0gmoc5dxevo03pj77l&st=82gn5bba&dl=0%22 (www.dropbox.com/scl/fi/b2ua0uswlinkte...)

Any ideas or explanations for why this is happening?

Thank you so much.

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Thank you for your reply! Yes, I have tried this and some low load cases do actually work with Paccl nearly zero and flat frequency. However, for those case that the spinning reserve/ P max in governer model cannot cover the generation deficit, the frequency still becomes flat with negative Paccl.

Wai (Feb 17 '5)

Can you show a raw data file of your test system?

perolofl (Feb 17 '5)

Thank you for your reply! I think I’ve figured out the reason for negative Paccl. I set the damping factor to 2 in the generator model “GENROU. Is that because Paccl is just “Pmech – Pelec” and doesn’t include the term Dω in the swing equation?

Wai (Feb 20 '5)

Also, I would also like to know how to determine the value for D. In addition, I would like to know the pros and cons of setting non-zero value for D in generator model and setting the frequency dependent term for P in the load model. Thank a lot!

Wai (Feb 20 '5)

Personally, I prefer to set D to zero in the generator model and to model the load frequency dependency with a load model, e.g. LDFRAL.

perolofl (Feb 20 '5)

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PSS/E Dynamic Simulation - Negative accelerating P but frequency not decreasing

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