Coordination Studies | Determining Device Priority

Achieving perfect coordination may seem as elusive as spotting a unicorn.  In order to obtain perfect coordination, overcurrent devices are selected and set so that only the device nearest a fault trips.  This minimizes the extent of an outage.  Although perfect coordination between all overcurrent devices is very difficult – bordering on impossible, making appropriate compromises and intentionally mis coordinating some less important devices makes it easier to coordinate more important devices.  The result: better overall selectivity for the system as a whole.   

Compromises? -Yes!  This approach requires evaluating the entire system and prioritizing the importance of each device.  Intentionally mis-coordinating devices seems counter intuitive and is certainly confusing.  However, it is one of the hidden secrets of successfully performing a coordination study. 

In this video, Jim Phillips explains a logical approach that can be used to define coordination priority and improve overall selectivity for the system. This is the approach that he adopted in the early 1980’s towards the beginning of his career (over 40 years ago but don’t tell anyone). Back then, he was responsible for developing software for performing coordination studies – Before there were PCs! This video is Module 15 of his 28 Module on-demand training program about performing coordination studies.