Specialist infrastructure investor group 3i Infrastructure said its portfolio is performing well and is positioned to deliver a strong yield.In the group's pre-close update from 1 April to 27 September 3i said movements in net asset value in the period will be influenced, among other factors, by the mark-to-market value of the junior debt portfolio, as well as currency movements.Chairman Peter Sedgwick said, "3i Infrastructure's portfolio continues to generate strong income, supporting the delivery of the company's distribution objectives."Managing Partner Cressida Hogg added, "Market conditions for infrastructure investment remain relatively supportive. The Investment Adviser is working on an attractive pipeline of investment opportunities in Europe and in India."At 27 September 2010 3i had cash balances of £297m and there are currently no external borrowings.