As @JoeySmyth pointed out, both PiDrive versions (314GB and 1TB) are designed for low power consumption and are powered by the Raspberry Pi itself.
The unique cable that comes with the kit gives you the option to plug external power into it, power the Pi AND the 1TB PiDrive and connect the drive to the Pi in order to transfer data between them without the need for any additional cables. The Kit also provides you with a power adapter (5V 3A) and a USB cable for it, 4GB microSD card and a SD card adapter and an enclosure for the Pi and the PiDrive.
The 1TB PiDrive is currently only available with the whole kit in our official WDStore.
Let me know if there’s anything else that I could be of help!