The relay type NA20 is typically used in HV, MV and LV 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.
Beside to the phase and residual overcurrent protection, the following protective functions are provided:
- Thermal image protection of lines and power transformers.
- Undercurrent protection for monitoring of CB opening.
- Negative sequence protection against asymmetrical short circuits and unbalance loads.
- I2/I1 protection against phase interruption under low-load condition.
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