Operation Principle - ABB Relion Technical Manual

Section 7
Impedance protection
7.3.7
170

Operation principle

The Loss of excitation (LEXPDIS ,40) protection in the IED measures the apparent
positive sequence impedance seen out from the generator.
Measured mode Measured apparent impedance
V
Z
posseq
posseq
=
I
posseq
EQUATION2051-ANSI V1 EN
There are three characteristics in LEXPDIS (40) protection as shown in figure 71.
Naimly:
• Offset mho circle for Z1
• Offset mho circle for Z2
• Directional blinder
X
IEC06000455 V2 EN
Figure 71: Three characteristics in LEXPDIS (40) protection
When the apparent impedance reaches the zone Z1 this zone will operate, normally with
a short delay. The zone is related to the dynamic stability of the generator.
(Equation 39)
Underexitation protection
Underexcitation Protection
Restrain area
Restrain area
R
R
Directional
blinder
Z1, Fast zone
Z2, Slow zone
IEC06000455-2-en.vsd
1MRK 502 048-UUS A
Technical manual