Application - ABB RELION REX640 Technical Manual

1MRS759142 C
4.4.4.6
REX640
Technical Manual
The operation of PREVPTOC can be described with a module diagram. All the
modules in the diagram are explained in the next sections.
I
I3P
2
detector
BLOCK
GUID-345DEF01-F242-4FEF-BA3F-48452E9555F8 V1 EN
Figure 416: Functional module diagram
Level detector
The level detector compares the negative-sequence current to the set Start value. If the
I value exceeds the set Start value, the level detector sends an enabling signal to the
2
timer module.
Timer
Once activated, the timer activates the START output. When the operation timer has
reached the set Operate delay time value, the OPERATE output is activated. If the fault
disappears before the module operates, the reset timer is activated. If the reset timer
reaches the value of 200 ms, the operation timer resets and the START output is
deactivated.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operation time. The value is available
in the monitored data view.

Application

The rotation of a motor in the reverse direction is not a desirable operating condition.
When the motor drives fans and pumps, for example, and the rotation direction is
reversed due to a wrong phase sequence, the driven process can be disturbed and the
flow of the cooling air of the motor can become reversed too. With a motor designed
only for a particular rotation direction, the reversed rotation direction can lead to an
inefficient cooling of the motor due to the fan design.
In a motor, the value of the negative-sequence component of the phase currents is very
negligible when compared to the positive-sequence component of the current during
a healthy operating condition of the motor. But when the motor is started with the
phase connections in the reverse order, the magnitude of I
the value of I exceeds the start value, the function detects the reverse rotation
2
direction and provides an operating signal that disconnects the motor from the supply.
Timer
Level
t
Section 4
Protection functions
OPERATE
START
is very high. So whenever
2
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