This is testing purpose in testing region. But actually it wiil be one full back up per day, differential back every 4 hour and transaction log every 1 hour. Actual problem is to the growing size of the transaction log though there is no transaction is performed. Two options are available in back up 1. Append and 2. overwrite to the file.

So my question is why the transaction log is growing with any of the option? Full backup file and differential back up file is not grwing for the same option overwrite when no transaction is performed.