How to add a Rules Condition to only allow voting for users with at least 30 user points? I want to put condition when userpoints>=30, then user is able to vote. 

For this, I did following steps-


ON event- "User votes on a node" the condition selected is "Compare current Userpoints" and in the condition part put ">=30".


I am using following modules: Rules, User Points and Vote Up/Down.
You should try to implement the hook form alter Drupal API: hook_form_alter

Within the hook_form_alter you can validate, if the current user has more then 30 Points and disable the voting widget if the value is below 30.