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Section 4
1MAC050144-MB C
Protection functions
204
615 series ANSI
Technical Manual
4.1.9
Negative-sequence overcurrent protection for motors, 46M
4.1.9.1
Identification
4.1.9.2
Function block
Figure 95:
Function block
4.1.9.3
Functionality
The unbalance protection based on negative sequence current 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.
4.1.9.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are Enable and Disable.
The operation of unbalance protection based on negative sequence current can be
described by using a module diagram. All the modules in the diagram are explained in the
next sections.
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Negative sequence time overcurrent
protection
MNSPTOC
I2>M
46M
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