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

asked 2018-10-11 04:55:40 -0600

Oridroo gravatar image

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)

Can anybody please guide me about this basic queries? Thanks in advance

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How did you change the rest of the generation when increasing solar? What type of governors do you have? Did the frequency minimum also decrease or just your calculated average RoCOF?

perolofl gravatar imageperolofl ( 2018-10-18 22:48:13 -0600 )edit

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answered 2018-10-17 22:44:21 -0600

Cao Huy gravatar image

updated 2018-10-23 22:18:30 -0600

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 formula:

RoCoF = f0Delta P/(2Hi*Si) with Delta P is the active power imbalance and Hi and Si is inertia and apparent power rating of generator i. Given the Hi of SPVs are zero. RoCoF are increase with increasing of SPV penetration rate.

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The formulas you present are not correct!!!

perolofl gravatar imageperolofl ( 2018-10-18 22:50:36 -0600 )edit

Which one do you mean? About the RoCoF, I need to clarify that the output is in 1/Sec. If you want to have ouput in Hz/Sec, you need to multiply the output with the rated frequency: f.

Cao Huy gravatar imageCao Huy ( 2018-10-23 05:31:32 -0600 )edit

The rotating energy for a generator is Hi*Si, where Si is nominal MVA rating. The formula is RoCoF = deltaP / (2*sigma(Hi*Si)) * fn [Hz/s]. The actual electrical power Pi for the generators does not affect the RoCoF.

perolofl gravatar imageperolofl ( 2018-10-23 06:11:46 -0600 )edit

My bads. Thank you. I have fixed the answer.

Cao Huy gravatar imageCao Huy ( 2018-10-23 22:09:17 -0600 )edit

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Asked: 2018-10-11 04:55:40 -0600

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Last updated: Oct 23 '18