Dear Inna,
As you and I recently discussed, although LEAP doesn't provide access to NEMO's transmission modeling features, SEI has developed an add-on for LEAP models that enables this functionality. With the add-on, LEAP models can simulate transmission networks and power flow.
I've separately sent the add-on to you, but I'm remarking on it here as well in case other users are interested in it. If so, please contact me, and I'll be happy to share the add-on and instructions for using it.
Regards,
Jason