Thus, as a general rule, the minimum number of capacitor units connected in parallel within a
SCB is such that isolation of one capacitor unit in a group should not cause a voltage
unbalance sufficient to place more than 110% of rated voltage on the remaining capacitors of
that parallel group. Equally, the minimum number of series connected groups within a SCB is
such that complete bypass of one group should not pause voltage higher than 110% of the
rated voltage on the remaining capacitors of that serial group. The value of 110% is the
maximum continuous overvoltage capability of capacitor units as per IEEE Std 18-1992.
The SCB typically requires the following types of IED protection:
1. Short circuit protection for SCB and connecting leads (can be provided by using PHPIOC,
OC4PTOC, CVGAPC, T2WPDIF/T3WPDIF or HZPDIF functions)
2. Earth-fault protection for SCB and connecting leads (can be provided by using EFPIOC,
EF4PTOC, CVGAPC, T2WPDIF/T3WPDIF or HZPDIF functions)
3. Current or Voltage based unbalance protection for SCB (can be provided by using
EF4PTOC, OC4PTOC, CVGAPC or VDCPTOV functions)
4. Overload protection for SCB
5. Undercurrent protection for SCB
6. Reconnection inhibit protection for SCB
7. Restrike condition detection
CBPGAPC function can be used to provide the last four types of protection mentioned in the
above list.
7.10.3 Setting guidelines
GUID-CECD6525-779C-4A77-844D-031AAEE3A5B6 v1
GUID-7C456976-BA0D-4AAC-9C7A-F73AF52B2B44 v2
This setting example will be done for application as shown in figure
114:
Preprocessing
Function Block
Capacitor bank
protection function
400kV
CBPGAPCSMAI
200MVAr
400kV
500/1
IED
IEC09000754-1-en.vsd
IEC09000754 V1 EN-US
Figure 114: Single line diagram for the application example
From figure 114 it is possible to calculate the following rated fundamental frequency current
for this SCB:
Section 7 1MRK 505 370-UEN D
Current protection
204 Busbar protection REB670
Application manual
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