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Application
The differential current relay type NT20 is intended for the
protection of two-winding power transformers,
auto-transformers and generator- transformer units.
Beside to the main differential protection (87T), the
following functions are provided:
Thermal image on one side,
Overcurrent on both sides,
Residual overcurrent or high impedance differential restricted
earth fault protection on one side,
Low impedance differential restricted earth fault protection
on one side.
No matching CTs are required.
Protective
functions
26 - Thermal probes
49 - Thermal image
50/51 - Phase overcurrent
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