Yes you can get an electricity connection bases on the possession certificate under the Release of new
LT Connections, Enhancement and Reduction of Loads) Regulations, 2007. as there under the proof of occupancy or ownership both are valid proof for the purpose of electric connection. So allotment letter, possession certificate and occupancy certificate based on these also an electric connection can be taken.
Kindly refer Rule required documents and formalities.
http://www.uerc.gov.in/Rules%20and%20regulation/UERCRegulations/Regulations%202013/English%20Regulations,%202013/UERC%20(Release%20of%20New%20LT%20Connections,%20Enhancement%20and%20Reduction%20of%20Loads)%20Regulations,%202013.pdf