# If Solar Generation increases in a power system, what is the expected effect on Rate of Change of Frequency (RoCoF)?

Hi, I am getting decreased RoCoF for increasing solar generation in my simulation result. I have doubt how valid this effect is? I used a simple formula to calculate this:

RoCoF= (Change in Frequency from Nominal Value till Frequency Nadir)/ (Time Required for this change)

     For example: if the system frequency is 50 Hz and the frequency Nadir is 49.5 Hz and it took 0.5 Sec to go from 50 to 49.5 Hz, then according to the above mentioned formula,

RoCoF = ((50-49.5)/0.5) (Hz/Sec)


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I think you should check following assumptions of your simulations:

1. Did your RoCoFs have the same time frame? Usually, people don't compare RoCoF of the different time frame.
2. Did you simulate the quick frequency response components? That may affect the RoCoF.
3. Check your primary frequency control? Is there any different in the droop of simulations? How many generations taking part in the frequency control in each case? How many active power reserve?

Theoretically, RoCoF at the instant of losing a generator is calculated by the formular:

RoCoF = Delta P/(2H) with Delta P is the active power imbalance and H is the weighted inertia constant of the system.

In which H is calculated by: H = Sigma (Hi*Pi)/(sigma Pi) with Hi and Pi is inertia and power output of generator i.

Given the Hi of solar generation is zero, the increasing in penetration rate of solar will reduce the H of system and increase the RoCoF at the instant.

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