code: def _varname_inj(self):
          
          # 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)
docs: Customize varname for bus injections