ABB 615 Series - Phase Selection Logic

The operation of 21FL can be described with a module diagram. All the modules in the
diagram are explained in the next sections.
BLOCK
TRIGG_XC0F
Phase
selection
logic
Fault
impedance
and
distance
calculation
TRIGG
ALARM
Trigger
detection
Alarm
indication
I_A
I_B
I_C
V_A_AB
V_B_BC
V_C_CA
I
0
I
1
I
2
V
0
V
1
V
2
Recorded
data
GUID-5DEC6352-438F-4B66-88F1-F72C0138AECF V1 EN
Figure 410: Functional module diagram
5.7.4.1 Phase selection logic
Identification of the faulty phases is provided by the built-in Phase Selection Logic based
on combined impedance and current criterion. Phase selection logic is virtually setting-
free and has only one parameter, Z Max phase load, for discriminating a large symmetrical
load from a three-phase fault. The setting Z Max phase load can be calculated using the
equation.
Z Max phase load = ⋅0 8
2
.
max
V
S
xy
GUID-BDFF7D0D-9323-4610-84C6-A9B4234136B3 V1 EN (Equation 137)
V
xy
Nominal phase-to-phase voltage
S
max
Maximum three-phase load
For example, if V
xy
= 20 kV and S
max
= 1 MVA, then Z Max phase load = 320.0 Ω.
The identification of the faulty phases is compulsory for the correct operation of 21FL.
This is because only one of the impedance-measuring elements (fault loops) provides the
correct result for a specific fault type. A three-phase fault is an exception and theoretically
1MAC059074-MB A Section 5
Protection related functions
615 series ANSI 805
Technical Manual