25 C.F.R. § 175.230
Why are changes to purchased power costs not included in the procedure for adjusting electric power rates?
Changes to purchased power costs are not included in the procedure for adjusting electric power rates because unforeseen increases in the cost of purchased power are:
(a) Not under our control;
(b) Determined by current market rates; and
(c) Subject to market fluctuations that can occur at an undetermined time and frequency.