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Application
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 lenght, while
in ungrounded or Petersen coil and/or resistance
grounded systems, the residual overcurrent protection
can be used on feeders of small lenght 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.
Protective
functions
50/51 - Phase overcurrent
50N/51N - Residual overcurrent
49 - Thermal image
37 - Undercurrent
46 - Negative-sequence overcurrent
I2/I1 - Phase interruption under low-load
condition
BF - Circuit breaker failure |
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