def _varname_inj(self):
        """Customize varname for bus injections"""
        # Bus Pi
        if not self.n:
            return
        m = self.system.dae.m
        xy_idx = range(m, self.n + m)
        self.system.varname.append(
            listname='unamey',
            xy_idx=xy_idx,
            var_name='P',
            element_name=self.name)
        self.system.varname.append(
            listname='fnamey',
            xy_idx=xy_idx,
            var_name='P',
            element_name=self.name)

        # Bus Qi
        xy_idx = range(m + self.n, m + 2 * self.n)
        self.system.varname.append(
            listname='unamey',
            xy_idx=xy_idx,
            var_name='Q',
            element_name=self.name)
        self.system.varname.append(
            listname='fnamey',
            xy_idx=xy_idx,
            var_name='Q',
            element_name=self.name)
Customize varname for bus injections