The difference in level between points of supports and the lowest point on the conductor is called sag.
When the conductor is suspended between two supports at some level, it takes the shape of a catenary. However, if the sag is very small compared with the span, then the sag-span curve is like a parabola.
The tension at any point on the conductor acts tangentially. Thus tension To at the lowest point O acts horizontally.
EXAMIANS