(a) The commissioners court may issue fully negotiable revenue bonds for the purpose of refunding bonds issued under this subchapter. An election is not necessary for the issuance of refunding bonds.
(b) The refunding bonds may be secured in the manner provided by this subchapter for securing original revenue bonds.

(c) Refunding bonds may be issued to refund bonds of more than one series or issue of outstanding revenue bonds and may combine pledges for the outstanding bonds for the security of the refunding bonds. Refunding bonds may be secured by other and additional revenues if the refunding bonds will not impair the contract rights of the holders or any of the outstanding bonds that are not to be refunded.
(d) Refunding bonds must be authorized by order of the commissioners court and shall be executed and mature as provided by this subchapter for original bonds.
(e) Refunding bonds must bear interest at the same or lower rate than that of the bonds refunded unless it is shown mathematically that a saving will result in the total amount of interest to be paid.
(f) Refunding bonds shall be approved by the attorney general as in the case of original bonds and shall be registered by the comptroller of public accounts on surrender and cancellation of the bonds to be refunded, unless the order authorizing issuance provides that the bonds are to be sold and the proceeds deposited in the place or places where the original bonds are payable. In that case, the refunding bonds may be issued in an amount sufficient to pay the interest on the original bonds to their option or maturity date, and the comptroller shall register them without the surrender and cancellation of the original bonds.
(g) Refunding bonds, after they have been approved by the attorney general and registered by the comptroller, are incontestable.