4.4.4
Negative-sequence overcurrent protection for machines 46M
4.4.4.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Negative-sequence overcurrent
protection for machines
MNSPTOC
I2>M
46M
4.4.4.2
Function block
PICKUP
I
2
46M
TRIP
BLOCK
BLK_RESTART
GUID-947A7DA2-8229-4A11-966B-3E3A4BA7F4AC V1 EN
Figure 305:
Function block
4.4.4.3
Functionality
The negative-sequence overcurrent protection for machines function 46M protects
electric motors from phase unbalance. A small voltage unbalance can produce a large
negative-sequence current flow in the motor. For example, a 5 percent voltage unbalance
produces a stator negative-sequence current of 30 percent of the full load current, which
can severely heat the motor. 46M detects the large negative-sequence current and
disconnects the motor.
The function contains a blocking functionality. It is possible to block the function outputs,
timers or the function itself, if desired.
4.4.4.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are “Enable” and “Disable”.
The operation of 46M can be described by using a module diagram. All the modules in the
diagram are explained in the next sections.
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
603
Technical Manual
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