Hello to experts out there,

I have a couple questions on the 78 out of step functions of the Siprotec 7UM622 relay:

Background:

Generator is busbar connected (meaning it is connected to the MV switchgear with out unit transformer). The MV switchgear is then connected to the national grid through a series of cable impedance and several sub-station transformers.

Questions:

1. How is the polygon angle, address 3508, is determine. Is this arbitrarily selected for convenience only or based on some data and does this affect the 78 function or none at all?

2. Is it true that by making characteristic 1 polygon wider and longer by assuming impedance Zc almost close to the grid (while the remainder of the total impedance is for characteristic 2) the relay zones becomes wider and more sensitive?   

Thank you very for your insight. It is appreciated.

Toring