Capacitor bank protection

In recent years the harmonic producing part of total load has increased continuously because of the massive usage of power electronic in all the voltage levels. Thyristor convertors, frequency convertors, thyristor switches and static var compensator, such as thyristor controlled reactors (TCR) and thyristor switched capacitors (TSC), are commonly adopted in industrial applications and power utilities.
Filter capacitor banks consist of capacitor bank and series connected air core. Their task is to absorb the harmonic currents generated by loads and all above mentioned power electronic devices.
The aim of NC020 is to provide a reliable and cost effective solution for such an application granting capacitor bank safe operations.



  • Breaker Failure - BF
  • Negative sequence overcurrent transformer - 46LT
  • Overvoltage - 59
  • Phase overcurrent side H and side L - 50/51


  • Modbus RTU RS232 protocol


NC020 Coding
Flyer NC020
NC020 Manual



The relay type NC20 provides protection of shunt capacitor banks and harmonic filter circuits. The capacitor banks may have the following configurations:

  • Single Wye grounded.
  • Single Wye ungrounded (with a resistor on the output of the neutral unbalance voltage transformer in order to develop the appropriate input current for the unbalance protection).
  • Double Wye ungrounded.
The capacitor banks may be: internally/externally fused or fuseless capacitor units. A suitable compensation method is provided to compensate the inherent unbalance neutral current
Protections 37, 49 and 50/51 (RMS) are based on RMS value measurement of the three phase currents (fundamental and harmonics up to the 11th)