Considerations for generator protection during black start conditions

This paper covers the application of sound relaying principles to help prevent unwanted tripping during black starts. An unwanted trip can be extremely detrimental to a utility attempting to reconnect its high-voltage grid and restore service throughout its operating region. This paper describes the analysis required to properly apply generator protection at stations with black start capability. A real-life case of a generator differential protection misoperation during a black start at a large hydro station is examined in detail to illustrate what steps to take to prevent these types of nuisance trips without sacrificing relay sensitivity. This paper also shows how to use a second generator differential element in tandem with the first to minimize the chance of an unwanted trip from occurring during a black start.