code: def voltage_delta_vde(v_nom, s_max, r, x, cos_phi):
      
      delta_v = (s_max * (
          r * cos_phi + x * math.sin(math.acos(cos_phi)))) / v_nom ** 2
      return delta_v
docs: Estimate voltrage drop/increase
  
      The VDE [#]_ proposes a simplified method to estimate voltage drop or
      increase in radial grids.
  
      Parameters
      ----------
      v_nom : int
          Nominal voltage
      s_max : float
          Apparent power
      r : float
          Short-circuit resistance from node to HV/MV substation (in ohm)
      x : float
          Short-circuit reactance from node to HV/MV substation (in ohm). Must
          be a signed number indicating (+) inductive reactive consumer (load
          case) or (-) inductive reactive supplier (generation case)
      cos_phi : float
  
      Returns
      -------
      :any:`float`
          Voltage drop or increase
          
      References
      ----------
      .. [#] VDE Anwenderrichtlinie: Erzeugungsanlagen am Niederspannungsnetz –
          Technische Mindestanforderungen für Anschluss und Parallelbetrieb von
          Erzeugungsanlagen am Niederspannungsnetz, 2011