If putting 7.5 hp variable frequency drive in 5 hp motor in elevator, May be due to regeneration (DBR put as per recommend) drive dc bus ckt failed recent out of 10 nos 8 nos burnt,any suggestion?

The variable frequency drive must be sized/rated for at least twice the KW rating of your motor, because the initial start up amp draw of the motor will be at least twice the rated amp draw of the motor.
Some VFD drive manufacturers probably have that already factored in, But the two to one sizing is a good rule of thumb.

Thank you all for comment still i am searching reasons as i was practically present on site and observes each and every point but Drive Size, DBR rating ,Line chock and parameter and also ac drive does not go in Regen. now i am focusing to wards noise.

you have already put the variable frequency drive in and if it is lifting the elevator then the drive is probably adequate the DC Bus is being damaged during the lowering of the elevator so you probably just need to put a larger DB in

The ac drive sizing of 7.5hp with a 5hp motor is due to debating requirements when running the variable frequency drive at high switching frequencies along with the starting torque requirements of the application. DBR need to be sized to match the braking IGBT within the drive as far as a minimum resistance is concerned. And the resistor needs to of sufficient kW's to take into to account the duty cycle of the braking.