Datasheet

K8AK-PM

Load-side Phase Loss

In principle, phase loss cannot be detected on the load side

because the K8AK-PM measures three-phase voltage to

determine phase loss.

Motor Load Phase Loss during Operation

Motor load phase loss cannot be detected during operation. It

can be used to detect phase loss at startup.

Normally, three-phase motors will continue to rotate even if

one phase is open. The three-phase voltage will be induced

at the motor terminals. The diagram shows voltage induction

at the motor terminals when phase R has been lost with a

load applied to a three-phase motor. The horizontal axis

shows the motor load as a percentage of the rated load, and

the vertical axis shows voltage as a percentage of the rated

voltage. The lines in the graph show the voltage induced at

the motor terminals for each load phase loss occurs during

operation. As the graph shows, phase loss cannot be

detected because the motor terminal voltage does not drop

very much even if a phase is lost when the load on the motor

is light. To detect motor load phase loss during operation, use

the undervoltage detection function to detect the motor

terminal voltages at phase loss.

Set the operating time carefully because it will affect the time

from when the phase loss occurs until tripping when this

function is used.

Characteristic Curve Diagram

Note: For phase loss of phase R. V

, V

, and V

indicate the motor

terminal voltage at phase loss.

Overvoltage Detection When Only One Phase Exceeds the

Overvoltage Set Value

The K8AK monitors each of the three-phase voltages. This

means an overvoltage is detected even if only one phase

exceeds the set value. The same applies to undervoltages.

Questions and Answers

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VTR

VRS

Note: This characteristic curve shows the approximate

values only.

Voltage (as a percentage of rated voltage)

Motor load (as a percentage of rated load)