The relay type NA011 can be used in radial networks as feeder or power transformer protection.
In solidly grounded systems the residual overcurrent protection can be used on feeders of any length, while in ungrounded or Petersen coil and/or resistance grounded systems, the residual overcurrent protection can be used on feeders of small length in order to avoid unwanted trippings due to the capacitive current contribution of the feeder on external ground fault.
The NA011 protection relay may be shipped with traditional CTs or low power (LPCT) current inputs; for both versions, the residual overcurrent protection can use the measured (CTs or balanced transformer) or the calculated residual current.

Applications
• Feeder
• Transformer
Protection functions
• Phase overcurrent (50/51)
• Residual overcurrent (50N/51N)
• Automatic reclosing (79)
• Breaker failure (BF)
Monitoring and control functions
• Cold Load Pickup (CLP)
• Digital Fault recording (DFR)
• Fault and event logging (SER & SFR)
• Self-test
Hardware
• 3 binary inputs + 4 output relays + 8 LEDs
• Auxiliary power supply 24-230 Vac/dc
• Flush mounting
• LPCT amperometric inputs
• Nominal current 1/5 A selectable by DIP-switch
• RS485 port
• Standard CT amperometric inputs 1/5 A
Communication
• Modbus RTU RS232 protocol
• Modbus RTU RS485 / IEC 870-5-103 / DNP3 protocol