ABB Relion 670 Series Applications Manual page 267

1MRK 511 401-UEN Rev. K
U
unit
IECEQUATION19279 V1 EN-US
U
unitRated
IECEQUATION19120 V1 EN-US
Where,
U
unit
U
unitRated
• The percentage increase in the voltage across the faulty unit is calculated as follows:
% U
IECEQUATION19121 V1 EN-US
Based on the number of fuse operations, the capacitance values in the system and differential
voltages in % of UBase are shown in the below table:
Table 44: Differential voltage calculation for ungrounded capacitor bank element failures
No of fuses C C
1
operated
0 36 Ce
1 34 Ce
2 32 Ce
3 30 Ce
4 28 Ce
5 26 Ce
6 24 Ce
7 22 Ce
8 20 Ce
9 18 Ce
10 16 Ce
11 14 Ce
12 12 Ce
13 10 Ce
14 8 Ce
15 6 Ce
16 4 Ce
17 2 Ce
According to IEEE Standard C37.99-2000, the capacitor bank must be removed from the
service when the voltage across the unit exceeds 110 % of the rated unit voltage. Hence, the
trip is given after 3 units failure in the faulty unit.
If the failure of the elements or the units results in the differential voltage of at least 1% of
UBase, the SCPDPTOV function detects the fault.
Figure 126
considered ungrounded capacitor bank.
Bay control REC670
Application manual
æ ö
C
= ´ ç
2
÷
U
L 1 +
è ø
C C
1 2
U
=
1 L
S
u
is the RMS value voltage across the faulty unit
is the rated RMS value voltage across the unit
U
= ´
unit
100
unit
U
unitRated
C U
2 L1
(pu)
36 Ce 18 Ce 0.5
36 Ce 17.4857 Ce 0.4857
36 Ce 16.9412 Ce 0.4706
36 Ce 16.3636 Ce 0.4545
36 Ce 15.75 Ce 0.4375
36 Ce 15.0968 Ce 0.4194
36 Ce 14.4 Ce 0.4
36 Ce 13.6552 Ce 0.3793
36 Ce 12.8571 Ce 0.3571
36 Ce 12 Ce 0.3333
36 Ce 11.0769 Ce 0.3077
36 Ce 10.08 Ce 0.28
36 Ce 9 Ce 0.25
36 Ce 7.8261 Ce 0.2174
36 Ce 6.5455 Ce 0.1818
36 Ce 5.1429 Ce 0.1429
36 Ce 3.6 Ce 0.1
36 Ce 1.8947 Ce 0.0526
shows the differential voltage variation with the number of unit's failure for the
© Copyright 2017 Hitachi Power Grids. All rights reserved
U UDIFL1
TapL1 N
(pu)
(pu)
0 0
0.0096 0.0382
0.0200 0.0788
0.0313 0.1222
0.0435 0.1685
0.0568 0.2181
0.0714 0.2714
0.0875 0.3289
0.1053 0.391
0.1250 0.4583
0.1471 0.5317
0.1719 0.6119
0.2000 0.7
0.2321 0.7974
0.2692 0.9056
0.3125 1.0268
0.3636 1.1636
0.4250 1.3197
Unbalance protection
(Equation 148)
(Equation 149)
(Equation 150)
PUDIFL1 %Uunit
(%UBase) (%)
0 100
3.8187 102.8571
7.8824 105.8824
12.2159 109.0909
16.8478 112.5
21.8109 116.129
27.1429 120
32.8879 124.1379
39.0977 128.5714
45.8333 133.3333
53.1674 138.4615
61.1875 144
70 150
79.736 156.5217
90.5594 163.6364
102.6786 171.4286
116.3636 180
131.9737 189.4737
Section 10
Decision
Trigger
Warning
Alarm
Trip
261