ABB Relion REC670 Applications Manual page 171

1MRK 511 358-UEN A
Capacitor Unit
(Can)
IEC09000753 V1 EN-US
Figure 76: Replacement of a faulty capacitor unit within SCB
There are four types of the capacitor unit fusing designs which are used for construction of
SCBs:
Externally fused
Internally fused
Fuseless
Unfused
Which type of fusing is used may depend on can manufacturer or utility preference and
previous experience.
Because the SCBs are built from the individual capacitor units the overall connections may
vary. Typically used SCB configurations are:
1. Delta-connected banks (generally used only at distribution voltages)
2. Single wye-connected banks
3. Double wye-connected banks
4. H-configuration, where each phase is connected in a bridge
Application manual
where an individual fuse, externally mounted, protects each capacitor unit.
where each capacitor element is fused inside the capacitor unit
where SCB is built from series connections of the individual capacitor units (that is, strings)
and without any fuses
where, in contrary to the fuseless configuration, a series or parallel connection of the
capacitor units is used to form SCB, still without any fuses
Rack
IEC09000753_1_en.vsd
Section 7
Current protection
165