Transient stability in digsilent

[nasim khalilnejhad]

Hello
I have result of transient stability of transmition network in digsilent,I want to know this network is stable or not.
Also if is not stable how can I solve the problem
Is there anybody to help me?

 

[beyond86]

Yes, it's unstable.
You have out of step condition for sym9910_1. Try to reduce clearing time of protection.

 

[nasim khalilnejhad]

Thanks alot
The short circuit time is 1 sec and fault clearing time is 1.1 sec

 

[beyond86]

1 sec is too long for such rotor angle.

 

[nasim khalilnejhad]

I mean short circuit occured at 1sec and clear at 1.1 sec

 

[beyond86]

Misunderstood you.
Try to reduce time to 20-30 ms. Initial rotor angle for sym9910_1 is close to critical, so in this case it will be difficult to keep stability under SC.

 

[nasim khalilnejhad]

I did it, a short circuit at 0.03 and clearing time at 0.23
But just the peaks transferred to earlier time.
I should say that there is a generator which I switch that out, the problem has been solve
I think there is swing between this two generators
But I don't know how to solve it,
I attached results
The second file is the condition which mentioned generator is out of service

 

[beyond86]

In this case, sym9910_1 has less rotor angel therefore out of step condition didn't happen.
I think this generator works with close critical rotor angel and even short disturbance lead to out of step.
Try to reduce active power for this generator and look at result.

 

[wcaseyharman]

What is this plot of? Is it a plot of a bus voltage angle or the actual generator rotor angle? If it’s the actual rotor angle, this is undamped generator disturbance, but the machines have not pulled out of step. If the machines pull out of step the rotor angles will trend toward very large values and the machine speed will increase above rated.
As an aside, I’ve modeled machines with no damping (they pre-date amortisseur bars) and they behave similarly to disturbances.