Capacitors and capacitor banks are used for various applications. Examples are: Reactive-power compensation for voltage stabilization, fast voltage- and reactive-power control or filter circuits for the elimination of certain frequencies. Capacitor banks for transmission systems are complex systems customized for the special application. The design depends much on the used switching technology (for example, mechanically or via thyristor). In detail hardly one capacitor bank resembles another. However, a capacitor bank consists always of the same components (C, R, L, and switches). A capacitor bank often consists of several subcomponents which are connected to the capacitor-bank busbar via the circuit breakers. The modularity of hardware and protection functionality allows to tailor the protection device exactly to the needs of the capacitor bank or the sub component of the capacitor bank and to realize the complete protection of the whole capacitor bank or the capacitor- bank sub component with only one SIPROTEC 7SJ8 device. Capacitor banks require the use of extensive protection functionality. The protection consists of standard protection functions and specific capacitor protection functions.