System Impact Study (Interconnection / SIS — Legacy)

The System Impact Study (SIS) was the detailed engineering study conducted under the prior serial LGIP process, evaluating the full impact of an individual Interconnection Request on the transmission system — including thermal overloads, voltage violations, and stability problems — and identifying required Network Upgrades with cost estimates. Under FERC Order No. 2023, the SIS was replaced by the Cluster Study, which performs equivalent analysis for groups of projects simultaneously and allocates upgrade costs using the Proportional Impact Method rather than the serial 'first-to-cause, first-to-pay' model. This term may still appear in legacy agreements and transitional queue proceedings.

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