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Unperturbed dynamic simulation is not stable.

asked 2022-11-13 11:21:43 -0600

CynicalSuka gravatar image

I have a case which is perfectly initialized but unperturbed dynamic simulation for the system is not what it should be. I should get constant value for power, angle etc. in unperturbed conditions but values keep changing haphazardly. Could be numerical instability. But my integration time step is also very small. so, no idea what it is. hope someone could clarify what is wrong with my case.

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answered 2022-11-14 10:43:08 -0600

perolofl gravatar image

Try to disable all exciter models (or governor models) and see if it makes it stable.

Another method is to enable "Display network convergence monitor" and check dynamic models located at or close to the bus with highest mismatch at the first iteration at each time step.

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Disabled all exciter and governor models. Getting same results. No change. See a change when i decrease DELT significantly.

CynicalSuka gravatar imageCynicalSuka ( 2022-11-15 20:48:10 -0600 )edit

Maybe a too short time constant in a generator model. Check the time constants in all generator models (GENSAL, GENROU, etc)

perolofl gravatar imageperolofl ( 2022-11-16 12:54:45 -0600 )edit

Don't think that i have that much small time constants. But will double check

CynicalSuka gravatar imageCynicalSuka ( 2022-11-17 10:23:38 -0600 )edit

Do you have SWS, HVDC or FACTS models?

perolofl gravatar imageperolofl ( 2022-11-17 10:59:59 -0600 )edit

Well my case do have sws and user-defined hvdc. But to leave no doubt i disabled them too. Infact right now i am just testing with simple example case which is 25 bus having only 2 generator just to test some things out. Just to check maybe something not right with simulation settings.

CynicalSuka gravatar imageCynicalSuka ( 2022-11-17 23:38:54 -0600 )edit

answered 2022-11-15 09:42:07 -0600

jconto gravatar image

Check this forum for "flat" or "flat start", like the posting "flat run for pv plant".
Usually, oscillatory behavior during flat runtime contains entry on the table "INITIAL CONDITIONS SUSPECT" saved in a log file. Models' parameter with "DSTATE" values being nonzero would required review to eliminate the problem.

Compare network and dynamic data against a previous data set that did flat-started (same basecase from last year?). Check your basecase for units and dynamic devices outside their operating range (Vmax, Vmin, Pmin, Pmax, Qmin, Qmax). Check the runtime log file for switching or tripping activity. As test, consider gnet units with worst oscillations, one at a time.

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my case has no initial condition suspects. Vmax Vmin etc limits are all correct. one strange thing that i noticed. when i make DELT=0.00001 then everything becomes flat. voltage, angle, etc. i ran the simulation for 5 seconds. perfect flat. although it took ages

CynicalSuka gravatar imageCynicalSuka ( 2022-11-15 13:30:54 -0600 )edit

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Asked: 2022-11-13 11:21:43 -0600

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Last updated: Nov 15