ABB RELION REX640 Technical Manual page 839

Protection and control

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1MRS759142 F

The operation of PREVPTOC can be described with a module diagram. All the

modules in the diagram are explained in the next sections.

Figure 475: Functional module diagram

Level detector

The level detector compares the negative-sequence current to the set

to the timer module.

Once activated, the timer activates the START output. When the operation timer

has reached the set

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.

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

So whenever the value of I

rotation direction and provides an operating signal that disconnects the motor

from the supply.

Technical Manual

value exceeds the set

Operate delay time value, the OPERATE output is activated. If

Start value , the level detector sends an enabling signal

exceeds the start value, the function detects the reverse

Protection functions

Start value . If

is very high.