late promotion policies in psu

iam working in ONGC as technical ASSISTANT from polytechnic background .but I did btech also..as per company policy I need to serve 18 year ( three promotions each 6 yrs) to became a officer level ASSISTANT executive engineer .these are time bounded promotions and no internal exams also ..so we have a btech qualification but we don't have a chance to get promotion faster or internal exams.but in other public sectors they have internal exams and fast promotion channels ...is there any possibility to get internal exams and fast promotion channels by putting case in court pls advice