InteliPro, SW version 1.4, ©ComAp –April 2014
InteliPro 1.4 Comprehensive Guide - rev. 1
Vector shift reaction times are usually requested up to 30ms. Typical setting is shown e.g. in G59/3
standard (see below).
Rate Of Change Of Frequency (df/dt, ROCOF, ANSI 81R)
ROCOF is second most frequently requested method of LOM detection. In principle, the method uses
similar evaluation method like Vector shift, but the physical phenomena detected is different. It
calculates the change of speed of the generator, caused by sudden change in its load, together with
unintentional islanding situation (loss of mains), which is normally capable of keeping the frequency on
a stable level. The frequency change is expressed as tangent in time [Hz/s]:
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