code: def validate(self, bigchain, current_transactions=[]):
          
  
          current_validators = self.get_validators(bigchain)
  
          super(ValidatorElection, self).validate(bigchain, current_transactions=current_transactions)
  
          # NOTE: change more than 1/3 of the current power is not allowed
          if self.asset['data']['power'] >= (1/3)*sum(current_validators.values()):
              raise InvalidPowerChange('`power` change must be less than 1/3 of total power')
  
          return self
docs: For more details refer BEP-21: https://github.com/bigchaindb/BEPs/tree/master/21