4.3.2 Stabilized and instantaneous differential protection for two-
winding transformers 87T
4.3.2.1 Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Stabilized and instantaneous differential
protection for two-winding transformers
TR2PTDF 3dI>T 87T
4.3.2.2 Function block
GUID-134E8524-738D-4232-A6BD-4C9BD2A62F8D-ANSI V1 EN
Figure 247: Function block
4.3.2.3 Functionality
The stabilized and instantaneous differential protection function 87T is designed to
protect two-winding transformers and generator-transformer blocks. 87T includes low
biased and high instantaneous stages.
The biased low stage provides a fast clearance of faults while remaining stable with high
currents passing through the protected zone increasing errors on current measuring. The
second harmonic restraint, together with the waveform based algorithms, ensures that the
low stage does not trip due to the transformer inrush currents. The fifth harmonic restraint
ensures that the low stage does not trip on apparent differential current caused by a
harmless transformer over-excitation.
The instantaneous high stage provides a very fast clearance of severe faults with a high
differential current regardless of their harmonics.
The setting characteristic can be set more sensitive with the aid of tap changer position
compensation. The correction of transformation ratio due to the changes in tap position is
done automatically based on the tap changer status information.
Section 4 1MAC059074-MB A
Protection functions
500 615 series ANSI
Technical Manual
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