def extend_substation(grid):
    """ Reinforce MV or LV substation by exchanging the existing trafo and installing a parallel one if necessary with according to dena

    Parameters
    ----------
        grid : :class:`~.ding0.core.GridDing0`
            Grid identifier.

    Returns
    -------
    type 
        #TODO: Description of return. Change type in the previous line accordingly
    """
    pass
