How does psse calculate frequency at bus?

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The bus frequency is calculated from the change in bus voltage angle. A filter is applied to smooth the frequency result, using a 0.04 s time constant for the filter. The frequency filter time can be changed in "Dynamic Solution Parameters".

To complete the previous answer, I have also realized that pss/e uses a 3rd order median filter, after doing the derivative. the output of the median filter then goes to a low path filter, with time constant of Tf, defined as Dynamic solution parameter.

Hello guys, thank you for your responses. So PSSE uses the derivative and washout filter for the bus calculations?

The Program Application Guide gives insight about the process of dynamic calculation but not about the method of frequency calculation at buses. Do you know where can I check this? Thanks

Regarding documentation, section 25.3 "Model NETFRQ" of the Program Application Guide (V2) has a bit of detail about the frequency filter, but no more detail than the answers here.