Subject to the limitations in this section, with the approval of the Board of Public Works, a State unit authorized to issue bonds may issue new bonds to refund its outstanding bonds. The power to issue bonds under this section is in addition to any other power to borrow. A State unit may issue bonds under this section only for: the public purpose of realizing for the State unit a savings in the total cost of debt service on a direct comparison or present value basis; the public purpose of debt restructuring that reduces the total cost of debt service; or the public purpose of debt restructuring that the State unit determines: is in its best interests; is consistent with its long term financial plan; and realizes a financial objective of the State unit, including improvement of the relationship of debt service to any source of payment such as taxes, assessments, or other charges. A State unit may: provide that bonds under this section be in 1 or more series; and vary the amount of the series. The total principal amount of the bonds issued under this section may exceed the total principal amount of the bonds that are being refunded. To determine whether the bonds under this section are within any limit on debt that applies to the State unit: the amount of the bonds that are being refunded shall be subtracted from its total outstanding debt; and the amount of the bonds issued under this section shall be added to the difference. Except as provided in paragraph (2) of this subsection, a State unit shall issue bonds under this section in accordance with the procedures that applied to issuance of the bonds that are being refunded. If, at a public meeting, the State unit determines that it would be in the public interest, the State unit may sell bonds issued under this section at a private sale, without soliciting bids. Bonds that are being refunded and that are subject to redemption before their stated dates of maturity may be called for redemption: on the earliest redemption date; or at a later date that the State unit determines. A State unit shall invest and apply proceeds of a sale of bonds issued under this section to ensure that the principal and redemption premium of, and interest on, the bonds that are being refunded will be paid in full when due. The State unit may deposit any part of the proceeds of the sale of bonds issued under this section in a trust fund with a trust company or other banking institution, in the name of the State unit. The trustee may invest and reinvest money in the trust fund in: obligations of the United States; obligations guaranteed by the United States; certificates of deposit or time deposits secured by an obligation of the United States; or certificates of deposit or time deposits secured by an obligation guaranteed by the United States. Interest, income, and profits on the investment may be: considered to be revenue of a revenue project; and applied in any lawful manner, including to the payment of: the bonds that are being refunded; and the bonds issued under this section. The trustee shall make money in the trust fund available, as the State unit requires, for the payment of: the principal and redemption premium of, and interest on, the bonds that are being refunded; the principal and redemption premium of, and interest on, the bonds issued under this section; or any other related costs. All or any part of the bonds issued under this section may be made payable from and secured by: money in the trust fund; or other money or security that the State unit provides.