VFD with multiple fan motors overcurrent protection 1

[LWFB]

I know the the overcurrent protection line side needs to be fast interrupt. What is the concensus for overcurrent on the load side with multiple fan motors.
Any concerns for multiple motors on single drive

Any help appreciated.

 

[buzzp]

You should have overload protection on each fan. The drive overload only protects the drive output and not the load, in your case.

 

[jraef]

Slight correction, you MUST have OL protection for each individual motor downstream from the VFD.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[artecerv]

This application note will also tell you what to do:

http://www.yaskawa.com/site/dmdrive.nsf/DocType.html?ReadForm&Start=1&Count=1000&Expand=3

AD4014 Application Data Multiple Motor Operation

 

[LionelHutz]

Be careful about using manual motor starters. The switch, breaker and overload all-in-one type of controller. Many of them will overheat on the output of a VFD. The ones I've seen have problems had a coil inside for the instantaneous overcurrent trip and that coil overheated.

 

[Drivesrock]

LWFB,

I would suggest that you choose OL relays so that the motor FLC is roughly in the middle of the adjustment range. There will be losses in the cables associated with the VFD PWM frequency and you may need to adjust the 'overload' protection for a little over the motor FLC to allow for that.
Please be aware that 'Instantaneous Overcurrent' - short circuits between phases or phase to earth - will not be protected against. The VFD will be much quicker at tripping (or at least should be!) than the relay opening when this kind of fault occurs. I believe it will be very dificult to find a relay that will trip on Instantaneous before the drive trips.
So this will mean that if one of your multiple motors or their cables has a short circuit fault then the drive will trip and all the motors will stop. Normally, this is rare! It will depend on your application.

Drivesrock.

 

[jraef]

Be careful about using manual motor starters. The switch, breaker and overload all-in-one type of controller. Many of them will overheat on the output of a VFD. The ones I've seen have problems had a coil inside for the instantaneous overcurrent trip and that coil overheated.

I have seen this too, but to be honest, the problem goes right away by simply putting a load reactor on the VFD output side (in front of the motor protectors), which has additional benefits when using multiple motors such as helping to protect the VFD from short circuits in the load wiring.

Eng-Tips: Help for your job, not for your homework Read faq731-376