Sum in dd:hh:mm:ss

Hi guys. I'm using a database of the duration time of the different trips that a set of vehicles made during the month. The data is in the format dd:hh:mm:ss. I would like to add these data (more than 300 rows) to obtain the total amount of time of the different trips and with this information get a lot more of averages and relevant information for my customers. The thing is that I can't get the sum.

For example:

A1: 00:17:41:24
A2: 0:01:39:00
A3: Sum(A1:A2)

But i just got 0:00:00:00

Please help me!!