Protection Engineering Basics and Schemes Protection Engineering | Page 77

here you can see the protection circuit, which is linked
with 13.8KV busbar, here one Potential Transformer is
connected line to ground for protection purposes.
whenever PT is connected line to line then line to line
voltage would be the PT output voltage, but when VT
connected between line to ground the output voltage
would be nominated voltage/sqrt(3)
here nominal voltage is 120V , so pt output would be
120/sqrt(3)=69.282V
here line need to be protected is 13.8Kv so voltage ratio
would be like
pg. 77
13.8 0.12 0.12
√3
:
√3
:
√3
Kv