Steam generators that currently correct their capacity ratings to reflect ambient temperatures make changes averaging less than 1%, meaning new rules requiring corrections of all steam units should not have a major impact on PJM operations.

The largest change among the units that currently correct — representing 58% of PJM’s installed capacity (ICAP) — was 2%.

“At least for the units that already temperature correct, we’re not seeing a major change in their ICAP ratings,” PJM’s Tom Falin told the Planning Committee last week.

About half of PJM’s steam units already adjust their ratings although Manual 21 requires adjustments only for combustion turbines and combined cycle plants. Falin said the committee will be asked to endorse manual language adding the correction requirements for nuclear, coal and oil units as soon as January.