ABB Relion 670 Series Applications Manual page 252

Section 10
Unbalance protection
Where,
V is the open-circuit voltage between U
th
Z is the open-circuit impedance between U
th
I is the unbalance current in Amperes
UNBL1
I is the phase L1 current in Amperes
L1
V is the RMS value of phase L1 voltage in Volts
L1
V is the RMS value voltage across the faulty unit
unit
%V is percentage of voltage across faulty unit with respect to the rated voltage
unit
V
unitRated
w is the radial frequency = 2 × π × f = 2 × π × 50
Based on the number of fuse operations, the calculated unbalance currents are shown in the
following table:
Table 38: Unbalance current calculation for grounded capacitor bank element failures
No of
fuses
operated
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
According to IEEE Standard C37.99-2000, a capacitor bank must be removed from the service
when the unit voltage exceeds 110% of the rated voltage. So, the trip is given after 12 elements
failure in the faulty unit.
246
is the RMS value rated voltage of a unit
C1 I I
UNBL1 L1
(A) (A)
(*Ce)
33.25 0 2368.8
33.18 1.25 2367.2
33.11 2.50 2366.4
33.04 3.74 2365.1
32.96 5.17 2363.7
32.88 6.61 2362.3
32.79 8.22 2360.7
32.69 10.05 2358.9
32.58 11.99 2356.9
32.47 13.97 2354.9
32.34 16.32 2352.6
32.21 18.66 2350.2
32.06 21.39 2347.5
31.89 24.47 2344.4
31.71 27.75 2341.1
31.51 31.40 2337.5
31.28 35.62 2333.3
31.02 40.40 2328.5
30.73 45.75 2323.1
© Copyright 2017 Hitachi Power Grids. All rights reserved
and U
1 2
and U
1 2
I I I
MEMUNBL1 MEML1 REFUNBL1
(A) (A) (A)
0.00 0.00 0.00
1.25 2367.2 1.25
1.25 2367.2 1.25
1.25 2367.2 1.25
1.25 2367.2 1.25
1.25 2367.2 1.25
1.25 2367.2 1.25
1.25 2367.2 1.25
1.25 2367.2 1.24
1.25 2367.2 1.24
1.25 2367.2 1.24
1.25 2367.2 1.24
1.25 2367.2 1.24
1.25 2367.2 1.24
1.25 2367.2 1.24
1.25 2367.2 1.23
1.25 2367.2 1.23
1.25 2367.2 1.23
1.25 2367.2 1.23
1MRK 511 401-UEN Rev. K
I %V Event
UNBCLCL1 unit
(A) (%)
0.00 100.00
0.00 100.55 Trigger
1.25 101.14
2.50 101.77
3.93 102.44
5.36 103.16
6.98 103.94
8.77 104.79
10.74 105.71
12.73 106.71
15.08 107.80
17.43 108.99
20.15 110.30 Trip
23.24 111.77
26.51 113.39
30.17 115.20
34.38 117.27
39.17 119.61
44.52 122.28
Bay control REC670
Application manual