Distance protection - Under reach & over reach

ailinfan

What is the meaning for under reach & over reach?

楚大少

Distance relay will compare the current and voltage that it measures and determine whether it is within its operation zone. However, there are some other factor that will influence the impedance that the distance relay will calculate. These factors include errors of CT & PT, saturation, line parameters error, etc. The influence of these factors is about 20% percent of the line impedance in total. So the distance relay set 80% of the line as instant operation zone -- zone 1. Zone 2 covers the rest 20% of the line with a delay of about 0.5 second. Zone 3 provides backup protection of the next line with a delay of about 0.8 second.
7 ]$ K! d  _; b% E
I hope this is helpful. You can read some books on protection relay or just go to wikipedia to find the information u need.

sjsky1984

Are you oversea chinese?