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)

Applications
• Bank capacitor / harmonic filter
Protection functions
• Pt100 thermometric probes (26)
• Undervoltage (27)
• Phase undercurrent (37)
• Negative sequence overcurrent (46)
• Neutral unbalance overcurrent with inherent unbalance compensation (46N)
• Thermal image (49)
• Phase overcurrent (50/51)
• RMS phase overcurrent (50/51(RMS))
• Residual overcurrent (50N/51N)
• Overvoltage (59)
• Breaker failure (BF)
• Discharge Timer (TD)
Monitoring and control functions
• CB diagnostic
• Cold Load Pickup (CLP)
• CTs monitoring (74CT)
• Digital Fault recording (DFR)
• Fault and event logging (SER & SFR)
• Logic selectivity
• Multiple setting profiles
• Programmable Logic Controller
• Self-test
• Trip circuit supervision (74TCS)
Hardware
• 2 binary inputs + 6 output relays + 8 LEDs
• Auxiliary power supply 110-230 Vac/dc
• Auxiliary power supply 24-48 Vac/dc
• Flush, projecting, projecting, rack, with separate MMI
• Network module with Ethernet FX port (optical fiber)
• Network module with Ethernet TX port (copper RJ45) + RS485 port
• Nominal current 1/5 A selectable by DIP-switch
• RS485 port (unavailable with Ethernet FX port)
• Standard CT amperometric inputs 1/5 A
Communication
• IEC 61850 Protocol
• Modbus RTU RS232 protocol
• Modbus RTU RS485 / IEC 870-5-103 / DNP3 protocol
• Modbus TCP/IP protocol (network board must be provided)