Differential Relaying and CT Error Calculations

[Dave Loucks]

Article 240.87 in the National Electrical Code describes using differential protection as one of the options to use if you have a breaker rated 1200 A or higher.  But just what is differential protection and why should or shouldn't be used?

This presentation gives an overview of how differential relaying operates and includes a discussion of CT accuracy and how high resistance loads (e.g. long CT conductors, small wire gauge CT conductors or high impedance loads) affect differential relaying accuracy.

Click on the image below to view a screencast of me presenting the contents in the attached PPT file below.