Voted Best Answer
Oct 29, 2018 - 05:40 AM
PSCAD (EMT type programs in general) solve the entire system after each time step, and solution of each step takes into account that of the previous step.
In your case, the output of the signal generator can change (i.e. from 1--> 0, 0-->1) after 1 time step. Since you set the frequency as 25 kHz, the signal generator output should change every 40 us (i.e. 1/25 kHz).If you set PSCAD time step at longer than 40 us, the signal generator would not be able to obtain any input from previous time step and it would be essentially hanging.
It is generally recommended that the time step should be set at 1/10th of time period of the highest frequency phenomenon to obtain reasonable result from EMT program. In your case it seems to be 4 us (in case you dont have any higher frequency phenomenon going on).
Hope that helps~