Capacitor Bank is needed to set proper protection systems to protect Capacitor bank against faults occurring within the bank including those inside the capacitor units, and to protect Capacitor bank against system diturbances and faults.
Generally, the method of detecting neutral value[voltage or current] is selected as the protection for capacitor bank system.
NVS is the protection system using voltage unbalance signals to alarm or shut down the bank in case of faults that may lead to significant damages.
To measure the unbalance of voltage, the voltage-sensing device[NVS] is used.
· Ungrounded Single Wye Banks
It detects the unbalance voltage between capacitor neutral and resistance which is connected with capacitor.
NVS of defecting voltage is changeable according to the number of internal series in capacitor.
· Ungrounded Double Wye Banks
It is the same protection method as ungrounded single Wye Bank.
The difference is that it detects the unbalance voltage between the two neutrals and it needs to use overvoltage relay.