4.4.4.2 Function block
GUID-5B6B4705-1EF3-4E12-B1A6-92A5D9D71218 V2 EN
Figure 246: Function block
4.4.4.3 Functionality
The unbalance protection based on the negative-sequence overcurrent protection
for motors MNSPTOC 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.
MNSPTOC 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 "On" and "Off".
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.
GUID-F890E844-B9C9-4E99-A51F-6EAB19B5239B V1 EN
Figure 247: Functional module diagram
Level detector
The calculated negative-sequence current is compared to the Start value setting. If
the measured value exceeds the Start value setting, the function activates the timer
module.
Section 4 1YHT530004D05 D
Protection functions
460 615 series
Technical Manual
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