ABB RELION REB500 Technical Manual page 69

1MRK 505 406-UEN B
voltage). Providing this is the case, the phase-angle of the impedance, that is, between fault
current and voltage, is determined:
arg
argZ = arg U - arg I
where,
• arg: argument of the complex number (angle)
• U: fault voltage
U = UL1 (phase-to-ground loop L1-E)
U = UL1 − UL2 (phase-to-phase loop L1-L2)
• I: fault current
I = IL1 (phase-to-ground loop L1-E)
I = IL1 − IL2 (phase-to-phase loop L1-L2)
arg Z must lie within the following limits for the fault to be designated a forwards fault:
-27° < arg Z < +117°
Arg Z must lie within the following limits for the fault to be designated a reverse fault:
+153° < arg Z < -63°
Z is the impedance measured by the protection, which corresponds to the line impedance Z
By using the fault voltage as reference voltage for determining direction, the measurement is
independent of source impedance.
If the fault voltage is less than the setting of the parameter
U (minimum fault voltage), the impedance is determined from the fault current and a
min
separate reference voltage:
arg
where,
• arg: angle (argument) of the complex number
• Uref: reference voltage
Uref = (UL2 – UL3) ⋅ ∠27° (phase-to-ground loop L1-E)
Uref = (UL1 - UL3) + 1/8 ⋅ (UL1mem – UL3mem) (phase-to-phase loop L1-L2)
• I: fault current
I = IL1 (phase-to-ground loop, for example, L1-E)
I = IL1 - IL2 (phase-to-phase loop, for example, L1-L2)
The reference voltage U
case of a phase-to-phase loop, the reference voltage also includes a proportion of the memory
voltage U
the power system frequency, depending on the discrepancy between the measured frequency
Bay protection functions REB500
Technical manual
U

Z arg
I
U
 
ref
Z arg arg U
ref ref
I
is derived from the phase voltages not involved in the fault. In the
ref
. The duration of the memory voltage is limited to between 5 and 15 periods of
mem
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
arg I
Section 5
Bay protection functions
.
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