By Michael Brooks

FERC on Thursday backtracked on several Tariff provisions it directed PJM to include in its implementation of a new cost allocation method for transmission projects that address stability issues (EL15-95-005, ER19-1501).

The commission granted rehearing of its Feb. 28 order accepting PJM’s stability deviation method for the limited purpose of removing the provisions from the compliance filing the RTO submitted in April. It directed PJM to refile its Tariff revisions without the provisions, leaving the new method as originally proposed.

The stability deviation method identifies the loads that would be most impacted by a stability disturbance — and thus benefit most from transmission projects that address stability-related issues — by measuring the voltage angular deviations during a simulated worst-case fault. Load buses with a deviation of less than 25% of the highest deviation would be excluded from the cost allocation. (See FERC: Stability Deviation Method Best for Artificial Island.)

In its original proposal, however, PJM identified a possible flaw in this plan: Once in service, the new transmission facility could address all stability issues, making it impossible to measure any angular deviations in a simulation. Several transmission owners also noted that the 25% threshold meant that under certain conditions, some deviations would be excluded from the cost allocation.

FERC directed PJM to include language to take the new facility out of the analysis if it resulted in deviations too small to measure when running the simulation. It also directed language that would allow PJM to adjust the 25% threshold as necessary.

In its April compliance filing, however, PJM said it had done further analysis and determined “that removing the stability upgrade would cause the model to go unstable and, therefore, fail to provide any meaningful information upon which to base the cost allocation.” Meanwhile, TOs American Electric Power, Dominion Energy, Duke Energy, FirstEnergy and PPL complained that the discretionary threshold provision would allow the RTO “to unilaterally determine the rate design under the PJM Tariff to recover the costs of a stability project based solely on PJM’s own discretion and with no approval or participation by” TOs.

To address both concerns, PJM asked FERC to delete the two provisions for now and give it some time to develop more Tariff revisions. FERC agreed.

“Accounting for these changed perspectives, we grant rehearing and remove both the deviation measurement provision and the discretionary threshold provision,” the commission said. It gave the RTO 30 days to refile its original proposal.