Authors: Prem Kumar, Dale Fredrickson, Koushik Chanda

The blackout of August 2003 caused misoperation of several system dependent protections of generators during the disturbance, exacerbating an already bad grid situation. Since then, there is increasing scrutiny on generator protection. The need to verify the operation of system dependent generator protection functions during system power swings is becoming increasingly important. Stability studies are needed to verify the impedance locus and expected relay operations for the various cases of power swings. In today’s deregulated energy market stability studies are typically performed by planning engineers of the transmission company or their consultants, and generator protection studies are performed by the protection engineers of the generating company or their consultants. Both studies are generally difficult to perform because of the amount of data required, different entities involved, and availability of engineers with a combined understanding of stability and protection.

This paper will provide a basic overview of stability studies and system dependent protection functions, will identify the required generation and transmission system parameters, present guidelines to perform a comprehensive study through an actual example, and will assist the generation and transmission engineers to achieve the desired result for system dependent generator protection functions.

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