Allow requestor approval - Not required in Payable invoice approval process

Hi Team,

Can any one suggest for below requirement.

Requestors should not allow to approve their own transactions in the Payable module.  A and B are the employees, Configured in AME approval hierarchy defined Org specific and Amount limits basis. How can we restrict self approval for employee A or B. If A raises the invoice it should go for B irrespective of amount.

Thanks

Chandra