ABB Relion 670 Series Applications Manual page 275

1MRK 511 401-UEN Rev. K
The trip level is based on protecting the capacitor units and fuses from the excessive voltages.
The alarm level is based on the early indication of the failures within the bank.
The number of blown fuses for the trip can be determined by the voltage on the capacitor
units in parallel with the faulty units and the capability of the units based either on industry
standards or the specifications provided by the manufacturer.
Therefore, the line-to-neutral voltage across the phase that includes blown fuses is calculated
as,
= +
V 1
LN
IECEQUATION19341 V1 EN-US
Then, the per unit voltage on the capacitor unit in the affected series group with the blown
fuses is calculated as,
V
=
V
CU
IECEQUATION19342 V1 EN-US
If C = 0 p.u., then
g
=
V V
CU LN
IECEQUATION19343 V1 EN-US
Table 46: Neutral unbalance voltage calculation for an ungrounded double WYE capacitor bank element failures
No of
Fuses
operated
(n)
0
1
2
3
4
5
6
7
8
Table 47
Table 47:
Name
BlockTrip
UMin>
CompEnable
UNUnbalWrn>
tDefWrn
UNUnbalAlm>
tDefAlm
Table continues on next page
Bay control REC670
Application manual
V
NG
´
C
LN S
C
g
´
S
u
C C C
g s p
(pu) (pu) (pu)
1 1 1
0.889 0.889 0.933
0.778 0.778 0.867
0.667 0.667 0.8
0.556 0.556 0.733
0.444 0.444 0.667
0.333 0.333 0.6
0.222 0.222 0.533
0.111 0.111 0.467
lists the recommended settings for the SCUVPTOV function in this example.
Setting of SCUVPTOV for an externally fused ungrounded double WYE capacitor bank
© Copyright 2017 Hitachi Power Grids. All rights reserved
V %V C
NG NG LN
(pu) (pu)
0 0 1
0.023 2.273 1.023
0.047 4.651 1.047
0.071 7.143 1.071
0.098 9.756 1.098
0.125 12.5 1.125
0.154 15.385 1.154
0.184 18.421 1.184
0.216 21.622 1.216
Default value
Trip enabled
75.0% of UBase
Enable
2.0% of UBase
5.00
7.0% of UBase
5.00
Unbalance protection
(Equation 155)
(Equation 156)
(Equation 157)
V %V Event
CU CU
(pu)
1 100
1.023 102.27 Warning
1.047 104.65
1.071 107.14 Alarm
1.098 109.76 Trip
1.125 112.5
1.154 115.39
1.184 118.42
1.216 121.62
Section 10
269