Stabilized And Instantaneous Differential Protection For Machines Mpdif (Ansi 87M/87G) - ABB RELION REX640 Technical Manual

Protection functions
4.3.7 Stabilized and instantaneous differential protection for
machines MPDIF (ANSI 87M/87G)
4.3.7.1 Identification
Function description
Stabilized and instantaneous differ-
ential protection for machines
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
I3P1
I3P2
788
See the preprocessing function blocks in this document for the possible
signal sources.
IEC 61850 IEC 60617
identification identification
MPDIF 3dI>G/M
Description
Three-phase currents
Three-phase currents
1MRS759142 F
ANSI/IEEE C37.2
device number
87M/87G
REX640
Technical Manual