ABB Relion 670 Series Applications Manual page 262

Section 10
Unbalance protection
Where,
PUDIFL1 is the differential voltage of phase L1 in % of UBase
• The voltage across the faulty unit is calculated as follows:
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 elements failure, the capacitance values in the system and the
differential voltages in % of UBase are shown in the
Table 41: Differential voltage calculation for grounded capacitor bank element failures
No of fuses C
1
operated
0 4.6667 Ce
1 4.55 Ce
2 4.4211 Ce
3 4.2778 Ce
4 4.1176 Ce
5 3.9375 Ce
6 3.7333 Ce
7 3.5 Ce
8 3.2308 Ce
9 2.9167 Ce
10 2.5455 Ce
11 2.1 Ce
12 1.5556 Ce
13 0.875 Ce
According to IEEE Standard C37.99-2000, the capacitor bank must be removed from service
when the voltage across the unit exceeds 110 % of the rated unit voltage. Hence, the trip is
given after 5 elements failed 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 123
failure for the considered grounded capacitor bank.
256
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 C
2 L1
4.6667 Ce 2.3333 Ce
4.6667 Ce 2.3038 Ce
4.6667 Ce 2.2703 Ce
4.6667 Ce 2.2319 Ce
4.6667 Ce 2.1875 Ce
4.6667 Ce 2.1356 Ce
4.6667 Ce 2.0741 Ce
4.6667 Ce 2 Ce
4.6667 Ce 1.9091 Ce
4.6667 Ce 1.7949 Ce
4.6667 Ce 1.6471 Ce
4.6667 Ce 1.4483 Ce
4.6667 Ce 1.1667 Ce
4.6667 Ce 0.7368 Ce
shows the differential voltage variation with the number of elements and units
© Copyright 2017 Hitachi Power Grids. All rights reserved
Table 41.
U UDIFL1 PUDIFL1
TapL1
(pu) (%UBase)
(pu)
0.5 0 0
0.4937 0.0127 1.2658
0.4865 0.027 2.7027
0.4783 0.0435 4.3478
0.4687 0.0625 6.25
0.4576 0.0847 8.4746
0.4444 0.1111 11.1111
0.4286 0.1429 14.2857
0.4091 0.1818 18.1818
0.3846 0.2308 23.0769
0.3529 0.2941 29.4118
0.3103 0.3793 37.931
0.25 0.5 50
0.1579 0.6842 68.4211
1MRK 511 401-UEN Rev. K
(Equation 136)
(Equation 137)
(Equation 138)
%Uunit Decision
(%)
100 Trigger
101.2658
102.7027
104.3478 Warning
106.25 Alarm
108.4746 Trip
111.1111
114.2857
118.1818
123.0769
129.4118
137.931
150
168.4211
Bay control REC670
Application manual