If there shall be filed with the board by any public utility an application requesting the board to determine the reasonableness of the utility’s rates, charges, schedules, service or regulations, the board shall promptly initiate a formal proceeding. Such a formal proceeding may be initiated at any time by the board on its own motion. Whenever such a proceeding has been initiated upon application or motion, the board shall set the case for hearing and give such notice thereof as it deems appropriate. Whenever the board, after a hearing held after reasonable notice, finds any public utility’s rates, charges, schedules, service or regulations are unjust, unreasonable, insufficient, discriminatory or otherwise in violation of any provision of law, the board shall determine just, reasonable, sufficient and nondiscriminatory rates, charges, schedules, service or regulations to be thereafter observed and enforced.