I think you can use synchronous generator with governor and treat as an external grid.

However, from my knowledge, it is better to calculate frequency from "Center of inertia" which is more practical.

You can find more about it in the link below:

https://www.researchgate.net/post/How_can_I_find_the_center_of_inertia_frequency_for_multi-machine_power_system

Dear Shubham,

I suggest you to take a look at link on subject.

(PDF) Adaptive Under-Frequency Load Shedding Considering Priority ...

https://www.researchgate.net/.../328569972_Adaptive_Under-Freq...

Best regards

Mohamed-Mourad Lafifi sir thanks for your kind reply. Can you please send the link again. I am not able to access it.

Hi,

Please use only the title of links and take a look at attached file on topic.

Adaptive Under-Frequency Load Shedding Considering Priority ...

The New Adaptive Under Frequency Load Shedding Technique in an ...

Best regards

Hi

DIgSILENT-wise!

If you simulate a network without external grid, in which the grid is just supplied by synchronous generators with properly tuned governors, changing the load and/or line and transformer outages, surely cause frequency deviation.

The same thing will happen when you have External grid in your network which possess station controllers such as governor, AVR, and PSS.

Obviously you need to simulate the network using the RMS/EMT simulation with an appropriate setting and step times.

I hope this helps!

Sincerely.

Hossein

Thank You sir for your kind response

Hi

I agree with Hossein Mahdinia Roudsari;

In addition to that:

You should use Electro Magnetic Transient analysis (EMT Simulation) of DIgSILENT.

The frequency would change if you change load value, provided you do not have swing bus.

Regards, Arash

Thanks a lot sir