code: def write_case_data(self, file):
          
          case_sheet = self.book.add_sheet("Case")
          case_sheet.write(0, 0, "Name")
          case_sheet.write(0, 1, self.case.name)
          case_sheet.write(1, 0, "base_mva")
          case_sheet.write(1, 1, self.case.base_mva)
docs: Writes the header to file.