The relay type NA21 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
STANDARD PROTECTIVE & CONTROL ELEMENTS
Phase overcurrent side H and side L - 50/51
Maximum Residual Overcurrent - 50N/51N
Automatic Recloser - 79
Breaker Failure - BF
CT Supervision - 74CT
Trip Circuit Supervision - 74TCS
Under Current - 37
Negative sequence overcurrent - 46
Thermal Image Transformer - 49LT
SW PACK OPTIONAL CONFIGURATION
Thermal with Pt100 Probes - 26
One USB Type B local port for communication with ThyVisor setup software
PRON NA21 IEC 103 Attestation of Conformity
XMR-A is a part of XMORE platform, the complete range of IEDs for Medium Voltage application including feeder, motor, generator, transformer and capacitor bank.
Thanks to Hardware and Software modularity XMR-A is flexible and scalable in term of application and performance as:
Overcurrent and Earth fault protection (StandardSW configuration)