
GENERAL
10
NA20 - Manual - 04 - 2022
2 G E N E R A L
2 G E N E R A L
Preface
The relay type NA20 is typically used in HV, MV and LV radial networks as feeder or power trans-
former 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 pro-
vided:
• 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.
• I
2
/
I
1
protection against phase interruption under low-load condition.
Following input circuits are available:
• Three phase current and one residual current inputs with nominal currents independently select-
able at 1 A or 5 A using dip-switch.
• Two or five (optional) binary inputs.
• One block input (logic selectivity).
In addition to the main protection element, the breaker failure (BF), CT monitoring (74CT), Trip Circuit
Supervision (TCS) and programmable logic (PLC) are also provided.
Setting, programming and reading operations must be effected by means of Personal Computer with
ThyVisor software or by means of remote communication interface (RS485 bus and Ethernet network
or USB); all operations must be performed through MMI.
According to the hardware configurations, the NA20 protection relay can be shipped in various case
styles depending on the required mounting options:
• Flush.
• Projecting mounting.
• Rack.
• With separate operator panel.
Other options are:
• Auxiliary power supply operating range.
• Communication protocols.
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Содержание NA20
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