# Calculating voltage drops in cables with vectors?

EVriderDK
Hey.

If i Have a 3x400VAC system, and I want to calculate the voltage drop over the cable "vectorially" - or what you call it :) - how do I do this?
U.nominal=400V

I have tried this method:
$\Delta$U.conductor=I.1*Z.cable1+I.2*Z.cable2+etc. and then I will have to find the new voltage ->
$\Delta$U.phase=U.conductor*$\sqrt{3}$
U.new=U.nominal-$\Delta$U.phase

When I'm calculating this with angles, I actually get a higher voltage, after the voltage drop :D
The voltage drop is cause by a electrical motor starting.

In school we learn it this way:
$\varphi$.motor=80 degrees

U.new=U.nominal-$\sqrt{3}$*I1*Length.cable1*(R.cable1*cos$\varphi$+X.cable1*sin$\varphi$)+$\sqrt{3}$*I2*Length.cable2(R.cable2*cos$\varphi$+X.cable2*sin$\varphi$)+etc.
But that is not with vectors.

Hope you understand?

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