Braking Resistor of VFD

[kimseunghee]

As I understand the braking resistor is always needed for VFD. Stater Vendor said that no resistor is need if pump come to stop very gradually and slowly. I am not not sure if it is right ? Is there abrupt increase in voltage during braking phase ?

 

[Skogsgurra]

The braking resistor is only needed if you need to stop the drive faster than it would stop when coasting down to zero speed.

You may, actually, stop a little faster than that without the resistor since losses in motor and inverter help reduce speed.

Many applications run without braking resistors. A mains failure stops the drive, but since drives universally get their control supply from the DC link, the energy in the load will keep DC link high until the drive has come to a standstill.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[gepman]

It is more common to have problems with VFDs slowing down fans than pumps (at least for me) since the moment of inertia on the fan can be higher and the frictional (slowing) forces lower. I have never had to put braking resistors on any of my pumping systems but I did see one on an oilfield pump that pumped over one mountain to a lower elevation, presumably for the syphon effect.

I am curious to know what situations that others have had to put braking resistors in pumping systems just so if I run into a similar situation that I can check out the requirement for braking resistors during the design stage in order to avoid the embarassment of adding them later.

 

[gepman]

My second paragraph in the above post may be interpreted as hijacking a thread. Please ignore it and my apologies to kimseunghee.

 

[chief]

Brake resistors (water cooled)are common in the oilfield drilling industry, especially to dissipate the energy from the Drawworks motors (approx 2000 -3000 hp).Also we use dynamic braking, where the hoist energy is dissipated by essentailly converting the hoist motors to generators by suitable switching arrangements. Another alternative is to regenerate the brake energy back to the grid. For smaller braking loads from Top drives , chopper resistors (air cooled) are common.

Offshore Engineering&Design

 

[controlsdude]

in the material handling industry, only use braking resistors where we stop and start conveyor real fast (< 5 seconds). For a sorter, if you have a ramp up and down at 15 seconds you do not need a braking resistor.

It depends on how much friction you have versus your ramp down time. Something you would have to play with if your not concerned with how much time it takes to ramp to a stop.