ABB RELION REX640 Technical Manual page 578

Section 4
Protection functions
572
sequence component on the star connected side that is earthed at its star point has to
be eliminated by using the Zro A elimination parameter.
The same parameter has to be used to eliminate the zero-sequence component if there
is, for example, an earthing transformer on the delta-connected side of the "Ynd"
power transformer in the area to be protected. In this case, the vector group matching
is normally made on the side of the star connection. On the side of the delta
connection, the elimination of the zero-sequence component has to be eliminated by
using the Zro A elimination parameter.
By using the Zro A elimination parameter, the zero-sequence component of the local
phase currents is calculated and reduced for each phase current:
1
− − −

I I I
LOC A _ = LOC A _ − ⋅ LOC A

3

GUID-2A5E838D-ECDA-43EE-87E4-06F46251C487 V2 EN
1
− − −

I I I
LOC B _ = LOC B _ − ⋅ LOC A

3

GUID-FB947BAF-6402-471D-A497-7AEA961B7D1A V1 EN
1
− − −

I I I
LOC C _ = LOC C _ − ⋅ LOC A

3

GUID-0B4023DE-019F-4BA6-9C5F-9BF4226BA720 V1 EN
Fail safe function
To prevent malfunction during communication interference, the operation of
LNPLDF is blocked when the protection communication supervision detects severe
interference in the communication channel. The timer reset stage is activated in case
the stabilized stage is started during a communication interruption. The protection
communication supervison is connected internally from PCSITPC to LNPLDF
(dotted OK line).
Protection
communication
supervision
(PCSITPC)
BLOCK
Operation "Test/blocked"
Operation "Off"
GUID-00D1CBD6-821D-4838-B536-51DBC3254603 V1 EN
Figure 313: Operation logic of the fail safe function
The function can also be set into "test/blocked" state with the Operation setting. This
can also be utilized during the commissioning.
The BLOCK input is provided for blocking the function with the logic. When the
function is blocked, the monitored data and measured values are still available but the
− −

I I
_ + LOC B _ + LOC C _


− −

I I
_ + LOC B _ + LOC C _


− −

I I
_ + LOC B _ + LOC C _


OK
AND
1MRS759142 C
(Equation 98)
(Equation 99)
(Equation 100)
PROT_ACTIVE
REX640
Technical Manual