Voltage Drop Calculation (AC)
Let's do this step by step. Shoving everything into one formula usually obscures what's happening.

0.0001ohms/s is quite big cable. 1mm2 cable is about 17mohms/m, so 0.1mohm/m means an area of 170mm2, which is a diameter of about 15mm. Is your cable that big?

140A in 0.1mohm gives 14mV voltage drop per metre.

300m of cable at 14mV/m is a total drop of 4.2v. Way above your figure, and we've not included the reactance yet, which will increase it.

What's that /1000 doing in your formula? Unless you understand why it's there, where it's come from, you might get answers that are 1000 times too small!