Above information provided by some members is not entirely correct.
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As per Indian Railway Refund rules for Partially traveled tickets, you are entitled to refund if claimed within 24 hours of disembarking en-route.
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Partially...
more... - used Reserved tickets
Time-limit: Within 24 hrs after the arrival of the train where you terminate your journey
Refund allowed: 50% of the fare for the untravelled portion of the journey, after retaining fare for the travelled portion subject to a minimum fare for 100 KMs
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However how you do it on an eticket is not clear anywhere. Its probably the online TDR route but you will need a certificate from the TTE that you have disembarked at the station you claimed. Even if you have that certificate, I am not sure how you would go about claiming what you are entitled to as per current rules.