Southwest Power Pool (SPP) filed amendments to its open access transmission tariff with FERC July 23, noting that the increase in non-dispatchable resources has rendered the current manual curtailment rules unworkable.
The amendments would facilitate the systematic rather than manual curtailment of non-dispatchable resources in the SPP energy imbalance market (EIS market) during congestion periods.
Currently, in the EIS market, certain resources are manually instead of systematically dispatched. These non-dispatchable resources traditionally have not been systematically dispatched through SPP’s market software tools to relieve congestion because of the uncontrollable nature of their output.
SPP also said there are several reasons why a resource would have an uncontrollable output, including that it may be an intermittent resource, such as a wind resource. Because of the uncontrollable nature of these non-dispatchable resources’ output, such resources often are unable to comply with a dispatch instruction to ramp up to a specific megawatt level and as a result, systematic dispatch of such resources has not been possible.
However, SPP said, such resources are able to reduce output when required to do so, so when SPP needs to curtail a non-dispatchable resource to relieve congestion, it issues a manual curtailment instruction to the resource through telephone.
When the manual curtailment rules were put in place for non-dispatchable resources, the amount of such resources in the SPP footprint was minimal, and manually dispatching such resources was enough to manage congestion. However, SPP added, since the beginning of the EIS market, the number of such resources and the megawatts of capacity in the SPP footprint have increased, rendering the manual curtailment of the resources unworkable.
Over the next three years, SPP expects the addition of more than 4,000 MW of non-dispatchable resource installed capacity in its footprint. “The significant increase in the amount of non-dispatchable resources has resulted in adverse economic and reliability impacts in the SPP region related to the manual dispatch of these resources,” SPP added.
The current manual curtailment of non-dispatchable resources impacts the SPP markets as well as the transmission system’s reliability. For instance, SPP added, having to dispatch these resources manually can block the quick resolution of an interconnection reliability operating limit exceedance, which must be resolved in 30 minutes or less.
Proposed new rules
To more efficiently dispatch and curtail non-dispatchable resources, SPP said it intends to modify its market operating system (MOS) and curtailment adjustment tool (CAT) software tools to allow automated and systematic curtailment instructions to be sent to non-dispatchable resources during congestion periods. These instructions systematically will direct a non-dispatchable resource to curtail its ouput instead of sending instructions that simply reflect the resource’s actual output at the time the EIS market solves for the next interval and that do not contemplate or instruct that the resources change the amount of their output, as is the case today.
Under the proposed new rules, during SPP congestion management events, non-dispatchable resources may be directed to operate at or below an adjusted maximum output level, and when directed, such a resource will be required to operate at the lower of its curtailment level or actual net output.
To determine such a resource’s curtailment level, SPP added that it will include the unscheduled portion of the output of non-dispatchable resources in the CAT curtailment calculations and assign a pro rata relief obligation in a way comparable to the obligations assigned to other impacting resources calculated by the CAT and NERC interchange distribution calculator (IDC). SPP will determine a maximum output level for each affected non-dispatchable resource based on the pro rata portion of the impacts of scheduled and non-scheduled output.
Non-dispatchable resources will be curtailed in accordance with their existing transmission service priority, which is based on whether the resource is scheduling against a transmission reservation, for instance.
The amendments to its tariff that SPP proposed include three new definitions for “exigent conditions,” “manual dispatch instruction” and “non-dispatchable resource,” as well as amendments to the definitions of “shut-down mode” and “start-up mode.”
Another amendment specifies that the impact of “unscheduled output from non-dispatchable resources” is included as part of the market flow impact on each coordinated flowgate and reciprocal flowgate that SPP submits to the NERC IDC, which will be used to determine the curtailment levels for all resources, including non-dispatchable resources.
While SPP requested an effective date of Oct. 15 for the amendments, it asked FERC to rule on the filing within 60 days so that SPP can complete the design, development and testing of necessary software to implement the changes on the effective date.