Tension required for wire rope for trolley

Dear sir, I want to know what will be tesion required for steel wire rope used to pull festooning cable for wagon loading machine. Size of the cable is 3 and half core copper cable of cross section area 10sqmm. Span is 150 mtr.And the dia of the steel wire will be either 16mm or 20mm.And sag we want not more than 50mm.

I will be pleased if you will show me the calculation

THanks.......