When designing a capacitor bank, many factors must be taken into consideration: rated voltage, kvar needs, system protection and communications, footprint and more. These factors govern the selection of the capacitor units to be used, along with proper grouping of these units.
Each unit should be rated 9.96 kV and 667 kvar. For a fuseless bank, capacitor units are only connected in series (illustrated in Figure 10); they are never placed in parallel like an externally or internally fused capacitor bank.
Figure L39 gives the minimum recommended cross section area of the upstream cable for capacitor banks. The minimum cross section area of these cables will be 1.5 mm 2 for 230 V. For the secondary side of the current transformer, the recommended cross section area is ≥ 2.5 mm 2 .
Bank stability for a fuseless capacitor bank is similar to that of an externally fused capacitor bank and defined by shorted series sections, internal to individual capacitors. The voltage on the remaining series sections in the string should not exceed 110% of its rated voltage.
Standard-duty capacitors are designed to the IEEE 18-2002 standard and are typically used in utility transmission and distribution applications, whereas heavy-duty capacitors are designed to the IEEE 18-2012 standard for applications where higher reliability is needed.
Capacitor banks require a means of unbalance protection to avoid overvoltage conditions, which would lead to cascading failures and possible tank ruptures. Figure 7. Bank connection at bank, unit and element levels. The primary protection method uses fusing.