def s_res(self, components=None):
        """
        Get resulting apparent power in kVA at line(s) and transformer(s).

        The apparent power at a line (or transformer) is determined from the
        maximum values of active power P and reactive power Q.

        .. math::

            S = max(\sqrt{p_0^2 + q_0^2}, \sqrt{p_1^2 + q_1^2})

        Parameters
        ----------
        components : :obj:`list`
            List with all components (of type :class:`~.grid.components.Line`
            or :class:`~.grid.components.Transformer`) to get apparent power
            for. If not provided defaults to return apparent power of all lines
            and transformers in the grid.

        Returns
        -------
        :pandas:`pandas.DataFrame<dataframe>`
            Apparent power in kVA for lines and/or transformers.

        """

        if components is not None:
            labels_included = []
            labels_not_included = []
            labels = [repr(l) for l in components]
            for label in labels:
                if (label in list(self.pfa_p.columns) and
                        label in list(self.pfa_q.columns)):
                    labels_included.append(label)
                else:
                    labels_not_included.append(label)
            if labels_not_included:
                logging.warning(
                    "Apparent power for {lines} are not returned from "
                    "PFA".format(lines=labels_not_included))
        else:
            labels_included = self.pfa_p.columns

        s_res = ((self.pfa_p[labels_included] ** 2 + self.pfa_q[
            labels_included] ** 2)).applymap(sqrt)

        return s_res
Get resulting apparent power in kVA at line(s) and transformer(s).

        The apparent power at a line (or transformer) is determined from the
        maximum values of active power P and reactive power Q.

        .. math::

            S = max(\sqrt{p_0^2 + q_0^2}, \sqrt{p_1^2 + q_1^2})

        Parameters
        ----------
        components : :obj:`list`
            List with all components (of type :class:`~.grid.components.Line`
            or :class:`~.grid.components.Transformer`) to get apparent power
            for. If not provided defaults to return apparent power of all lines
            and transformers in the grid.

        Returns
        -------
        :pandas:`pandas.DataFrame<dataframe>`
            Apparent power in kVA for lines and/or transformers.