# How to manually implement load dropping (exact MW amount) during dynamic simulation?

I need to see the impact of varying load dropping amount to system frequency after tripping of a large generating plant. For easier execution especially with scenarios requiring thousands of MW of load to be dropped due to multiple outages of generating plants, I tried to use SCAL activity to reflect my desired amount of load to be dropped. However, upon checking based on the initial and final load total through SCAL activity, the desired amount of load drop was not accurately reflected. It is essential for my study to determine the frequency response given the exact amount of total load drop.

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Use load shedding relays. Check the "Model library" manual for the relay model LDSHxx. As an example: dyr entry to drop a fraction of total system load for a 60 Hz system, three load shedding stages of 5%, 10%, 10% load shedding relative to initial load:

//[UFLS Models]
// I, 'LDSHxx', LID,  f1  , t1,   frac1,  f2,   t2,   frac2,   f3,   t3,   frac3,   Tb
0, 'LDSHAL',   * , 59.3, 0.15, 0.05,   58.9, 0.1,  0.1,     58.5, 0.0,  0.1,     0.08 /


Using a single stage run, a fraction value would represent a fixed percentage of total load to drop whenever the trigger point (set by f1 and t1) is reached. Repeat the run for multiple values of the fraction of load to be shed. Here a python script to automate the study will be very helpful.

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Thank you for your response, jconto. Is it also possible to use Activity SCAL in dynamic simulation so that I can directly input the MW amount of load shedding without considering UFLS model?

( 2020-07-09 02:22:23 -0500 )edit

For a dynamic study is better to use dynamic activities like the use of relays to drop 'dynamically' a load instead of using steady state activities like SCAL. What would be a reason not to use load shedding relays?

( 2020-07-09 09:14:52 -0500 )edit

jconto: I think OP is more interested in the frequency response as a function of dropped load as opposed to validating a LDSH model. OP: SCAL should allow you to specify an explicit MW amount, perhaps you were scaling relatively?

( 2020-07-09 13:08:18 -0500 )edit

I agree that it is not about validating a relay model. In a dynamic simulation, the system experienced the loss of generation, now load will be drop. By using a UFLS relay model with one stage, you can simulate the drop of x% of total load, instantaneously if t1=0, when frequency drop to f1 value.

( 2020-07-09 14:35:16 -0500 )edit