Beat eggs 2 minutes at medium speed of electric mixer; add sugar, beating well. Add rind, juice, and oil; mix well.
Combine flour, baking powder, and salt; add to egg mixture, beating until smooth.
Drop batter by level tablespoonfuls into deep oil heated to 375°. Fry until golden, turning once. Drain well on paper towels. Roll each doughnut in powdered sugar.