Welcome to the OEM forum, Samir.
The good news is you can use your RPi 3. The bad news is you might be able to use your current transformers, but without knowing exactly what they are (in terms of their ratio, their current output at rated current and their VA rating), I cannot say definitely that you can use them.
What I think you need is an emonTx V3.4, 3 YHDC 100 A c.t’s to measure your 3 phase incoming lines, a 9 V a.c. adapter to measure one of the voltages, a programmer to enable you to load the 3-phase sketch into your emonTx, and you might also need a 5 V d.c. USB power supply for the emonTx; and for your RPi, you either need a RFM69Pi radio module for it to receive by radio the data from your emonTx, or if the emonTx and RPi can be located close together, then you can connect them serially.
The RPi needs emonCMS (which you can either download or you can buy a pre-programmed SD card), and it will receive your temperature data via Wi-Fi (or wired Ethernet).
Before you buy, you might like to look at the download for the 3-phase sketch. In the zip file, you’ll find documentation with all the details that you need to configure and calibrate it.