# Quantiative criteria for instability system

Hi, all. I'm trying to analyse angle stability of machines in the system, which costs me a lot of time because I have to run dynamic simulation over and over again to find CCT (critical clearing time).

That's so I came up with an idea to run it automatically. The script isn't so hard, I guess I can deal with it, but the problem is how to identify if a system stability or not.

Manually, I could say if a system is instability by some signs, such as that machines' speeds and angles are seperated largely, or voltages drop below 0.5 (voltage stability), etc. However, defining a quantitative criteria which works for every machines in the system is not as easy.

I came some ideas for the criteria, but not so sure about them:

1. the difference between any 2 machine's angles isn't bigger than 100 degree.
2. The difference between any machine's speed and the average speed of the system must be smaller than 0.1. Average speed is calculated like this: Sum((Machine speed)*(machine inertia constant))/ (Sum Inertia constants)
3. d Delta/dt turn sign (from negative to positive or vice visa) more than once, in which Delta is the difference between angle of interested machine and reference machine.

I want to know is there any available function in pss/e that can distinguish instability system? If not, is there any other idea to make it?

edit retag close merge delete

Sort by ยป oldest newest most voted

If you are purely after rotor angle stability then monitoring angle spread would probably be your best option, which corresponds to your (1). The easiest way to approach this would be using the SYSANG model .

Alternatively, you may also make use of OSSCAN model (monitoring only), which scans for out-of-step conditions. However you would need to parse PSS/E progress printing for out-of-step messages.

more

All your three criteria are related to machine angle. For simplicity I prefer the first.

Instability of the system is about how the remaining system performs post-fault conditions, subject to all tripping activated by the protection system. Does it reach a stable condition (in V, F) at the end of the simulation? Good and sufficient modeling is needed for this kind of assessment.

For a test event, system instabilty can be monitored by:

• angle of generators, relative to reference machine like a nuclear plant or base unit. [generic model available in PSSe] Realistic criteria for the protection relays is needed (why trip a unit when its relative angle is 100 deg and not at 120 deg.?) Tripping of a unit might not render a system unstable.

• buses voltage level leading to voltage collapse or high-voltage cascading. Add UVLS relays [generic v-monitoring model available in PSSe, also UV/OV relays] Add load dynamic model reflecting V & F dependance. Air-conditioner loads?

• undamped oscillation, is damping > 3%?. Use Prony analysis after filtering visually all plots.

• system frequency (or Pelectric - Pload), add UFLS relay and UF/OF relays.

CCT studies help to set the initial protection of generators for angle separation but not needed to assess the stability of a system. Dynamic stability studies take time, need running multiple scenarios under many fault tests. I recommend driving PSSe in parallel processing for that (or CCT studies ;)

more

Dear Mr.Huy, I'm Phat, student at Ho Chi Minh City University of Technoly. I'm doing thesis related to PSS/E, Python and I think I need your help. Please give me your email or contact me: 41202668@hcmut.edu.vn. Regards!

more