I don't know for which exam you are asking this. But in general, there are no such norms known about the Voter Card to be a valid identity in the examination center. You can consider any of the Unique Identification card such as License, Passport, Aadhar card etc.

Now if its written that you need to bring it then you have to take your admit to the examination center.

To know more about CU visit the link below:

https://www.careers360.com/university/university-of-calcutta-kolkata

I hope this answer helps. All the very best for your future endeavors!