How to get Refund for the Train Ticket-Railway Rules

How to get Refund for the Train Ticket-Railway Rules 

Refund in case of train late more than 3 hours: In case train is late more than 3 hours, refund is admissible as per railway refund rules only when TDR is filed by the user before the actual departure of the train at boarding station and passenger has not travelled.

Source:IRCTC