ABB Relion 670 Series Applications Manual page 160

Section 8
Current protection
³
I 1
step2
EQUATION1203 V4 EN-US
where:
I
step1
Step 3
This step has directional function and a time delay slightly larger than step 2, often 0.8 s. Step
3 shall enable selective trip of earth faults having higher fault resistance to earth, compared to
step 2. The requirement on step 3 is selectivity to other earth-fault protections in the network.
One criterion for setting is shown in Figure 77.
3I
0
IN
>
IEC05000156 V3 EN-US
Figure 77:
³
I 1
step3
EQUATION1204 V4 EN-US
where:
I
step2
Step 4
This step normally has non-directional function and a relatively long time delay. The task for
step 4 is to detect and initiate trip for earth faults with large fault resistance, for example tree
faults. Step 4 shall also detect series faults where one or two poles, of a breaker or other
switching device, are open while the other poles are closed.
Both high resistance earth faults and series faults give zero-sequence current flow in the
network. Such currents give disturbances on telecommunication systems and current to earth.
It is important to clear such faults both concerning personal security as well as risk of fire.
The current setting for step 4 is often set down to about 100 A (primary 3I
applications definite time delay in the range 1.2 - 2.0 s is used. In other applications a current
dependent inverse time characteristic is used. This enables a higher degree of selectivity also
for sensitive earth-fault current protection.
8.4.4.7 Phase selection element
The phase selection feature is controlled by the setting
output PHSELL1, PHSELL2, and PHSELL3 from EF4PTOC shall be connected to phase selection
inputs PS1L, PSL2, and PSL3 of the trip logic SMPPTRC, as shown in
154
3I
0
× ×
.2 I
step1
3I
0 1
is the current setting for step 1 on the faulted line.
Step 3, Selectivity calculation
3I
0
× ×
.2 I
step2
3I
02
is the chosen current setting for step 2 on the faulted line.
© Copyright 2017 Hitachi Power Grids. All rights reserved
1MRK 511 401-UEN Rev. K
3I
02
IN >
One phase-to-
earth fault
IEC05000156-3-en.vsd
). In many
0
GUID-8C11DEA0-5786-4839-9EAF-2DFDB9ECE216 v1
EnPhaseSel . The phase selection
Figure 78.
Bay control REC670
(Equation 46)
M15282-164 v6
(Equation 47)
M15282-177 v4
Application manual