16.1 APPLICATION NOTES
16.1.1 ANTI-BACKSPIN PROTECTION
A motor may be driving a very high inertia load. Once the CB/Contactor supplying power to the motor is switched
off
, the rotor may continue to turn for a considerable length of time as it decelerates. The motor now becomes a
generator and applying supply voltage out of phase can result in catastrophic failure. In some other applications
for example when a motor is on a down-hole pump, after the motor stops, the liquid may fall back down the pipe
and spin the rotor backwards. Don’t start the motor at this time. In these circumstances the anti-backspin function
is used to detect when the rotor has stopped, to allow re-starting of the motor.
The operation of this function depends on the parameter VT connecting mode. If this is set to Vremanent, then the
function uses an undervoltage with the connected Phase-Phase remanent voltage. If not, the function uses only a
time delay.
Setting guidelines
The voltage threshold setting for the anti-backspin protection VRem Antibacks should be set to a low value to
indicate that the motor is stopped. The default setting of 10 V secondary is adequate for most applications.
The Anti-backs Delay must be set to an adequate time for the motor to stop after the trip. The default setting of
3000 s is adequate for the majority of applications.
P24xM Chapter 6 - Current Protection Functions
P24xM-TM-EN-2.1 163
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