Delta-connected banks are generally used only at distribution
voltages and are configured with a single series group of capacitors rated at
line-to-line voltage.
Delta-connected banks require a two bushing capacitor or
single-bushing units with insulated racks.
Delta-connected banks are frequently used at 2400 V because
capacitor units for wye connection at 2400 V are not readily available.
With only one series group of units, no overvoltage occurs
across the remaining capacitor units from the isolation of a faulted capacitor
unit.
Therefore, unbalance detection is not required for
protection, but may be used to detect the outage of units within the bank.
No zero-sequence or third harmonic currents can flow into a
delta-connected capacitor bank.
Where one series group per leg is used, the individual
capacitor fuses shall be capable of interrupting the system short-circuit
phase-to-phase fault current. This design may necessitate current-limiting
fuses.
If internally fused capacitor units are used, unbalance
detection is required to detect a capacitor with failed elements. There is no
visible indication of a blown fuse.
Two or more series groups are normally required in each
capacitor unit to enable the internal fuses to interrupt the fault current.
Static var compensator usually uses the delta connection for
the thyristor-switched capacitors (TSCs) to simplify the controls and optimize
the use of the thyristor valve.
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