4.3.7 Stabilized and instantaneous differential protection for
machines MPDIF (ANSI 87M/87G)
4.3.7.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Stabilized and instantaneous differ-
ential protection for machines
MPDIF 3dI>G/M 87M/87G
4.3.7.2 Function block
Figure 448: Function block
4.3.7.3 Functionality
The stabilized and instantaneous differential protection for machines function
MPDIF is a unit protection function. The possibility of internal failures of the
machine is relatively low. However, the consequences in terms of cost and
production loss are often serious, which makes the differential protection an
important protection function.
The stability of the differential protection is enhanced by a DC restraint feature.
This feature decreases the sensitivity of the differential protection optionally for
a temporary time period to avoid an unnecessary disconnection of the machine
during the external faults that have a fault current with high DC currents. MPDIF
also includes a CT saturation-based blocking which prevents unnecessary tripping
in case of the detection of the magnetizing inrush currents which can be present at
the switching operations, overvoltages or external faults.
4.3.7.4 Analog channel configuration
MPDIF has two analog group inputs which must be properly configured.
Table 716: Analog inputs
Input Description
I3P1 Three-phase currents
I3P2 Three-phase currents
See the preprocessing function blocks in this document for the possible
signal sources.
Protection functions 1MRS759142 F
788 REX640
Technical Manual
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