Why i can not connect my external hard drive to my phone yureka? When i connect my lenovo external hard drive to my phone yureka by the combination of otg cable,y cable and the power bank .
It shows constantly the message that connected and disconnected .
Please help me sir...
This trick you are trying to do, does not depend upon any single condition. To connect an external hard drive to phone with the help of USB-OTG requires to satisfy both hardware and software compatibility. 


as you said 'when you tried to connect external hard drive it shows constantly connecting and disconnecting', this maybe issue of power needed to support external hard drive. I guess your device has 5 V battery of capacity 2500 mAh. To mount 1 tb device on that power puts tremendous work load on Android device. ( there are devices like OnePlus or nexus with bigger specifications that can do this job so it's definitely not a 'impossible' thing) 
In case of software, your phone or phones file system might not have compatibility with the file system of external hard drive. Try to use different file explorers like ES File Explorer or there is an app available on play store named 'paragon' that can mount ntfs hfs+ and other file systems (requires root) . and then check again. 


before writing this answer i tried connecting my own Seagate backup+ 1TB  hard drive to my xiaomi redmi note 3. It shows notification 'Blank usb storage or unsupported file system'. my device has 4000 mAh battery and notification is not fluctuating so i guess its software issue in case of me and hardware issue in case of you.