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Section 7
Current protection
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
This setting example will be done for application as shown in figure 114:
200MVAr
400kV
IEC09000754 V1 EN-US
Figure 114: Single line diagram for the application example
From figure
for this SCB:
204
400kV
500/1
114
it is possible to calculate the following rated fundamental frequency current
Preprocessing
Capacitor bank
Function Block
protection function
SMAI
1MRK 505 370-UEN D
GUID-CECD6525-779C-4A77-844D-031AAEE3A5B6 v1
GUID-7C456976-BA0D-4AAC-9C7A-F73AF52B2B44 v2
CBPGAPC
IED
IEC09000754-1-en.vsd
Busbar protection REB670
Application manual
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