ABB Relion 670 Series Applications Manual page 274

Section 10
Unbalance protection
L3
L2
L1
Su = 1
Blown
fuses
IEC19000929 V1 EN-US
Figure 129: Units arrangement in an ungrounded double WYE connected capacitor bank
The per unit capacitance of the parallel group of capacitors that include the blown fuses is
calculated as,
P
=
a
C
g
P
IECEQUATION19337 V1 EN-US
Where,
P is the number of parallel units in the affected section = 9.
a
n is the number of blown fuses.
The per unit phase-to-neutral capacitance of the series or parallel group of capacitor units that
include blown fuses is calculated as,
=
C
s
C
IECEQUATION19338 V1 EN-US
Where, S
The per-unit capacitance of the phase (both WYEs) that includes blown fuses is calculated as,
(
=
C
p
IECEQUATION19339 V1 EN-US
Where,
P is the number of parallel units per phase = 15.
u
For a single WYE bank, P
Because of the element failure in the left section, per unit (of line-to-ground voltage)
unbalance voltage in the neutral is calculated as,
=
V
NG
2
IECEQUATION19340 V1 EN-US
268
Cu
N1
Pa = 9
-
n
a
´
S C
u g
( )
´ - +
S 1 1
g u
is number of series groups = 1.
u
)
´ + -
P C P P
a s u a
P
u
= P and C
a u
3
-
1
+
C
p
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Cu Cu
= C .
p s
1MRK 511 401-UEN Rev. K
Cu Cu
N2
IEC19000929-1-en.vsdx
(Equation 151)
(Equation 152)
(Equation 153)
(Equation 154)
Bay control REC670
Application manual