VFD or Contactors

[marwanco]

Hello All,

I used to control 15HP pump motor with reversible contactors and overloads.

What advantage will I have if I go for VFD solution instead.

Any cost saving? Will I eleminate overload?maybe other advantages?

I can run pump slower by reducing frequency, this is small advantage to me.

Thanks
MHH

 

[mesutphen]

The only two advantages to VFD's that I've seen have been speed control and reduced starting current. A VFD is more expensive than a reversible contactor. While you can realize some electricity savings in running the pump at a reduced speed, it is doubtful that you will recoup the added cost. The VFD will not eliminate the overload. If the advantage of running the pump slower is worth the added cost, then go for it. A VFD is not horribly expensive, just more expensive than the reversible contactor.

 

[jraef]

All modern VFDs now include overload protection. In general, the crossover as far as cost goes compared to a reversing starter is at about 10HP (or 5HP at 230V), so at 15HP, the VFD is going to cost you a little more. it still might be worth it though, because it does provide soft starting, which can save on wear and tear of your mechanical components, plus there is the POTENTIAL* for energy saving. You have to consider though that a VFD also adds a level of complexity to your control system considerations, something that may be problematic for some operators.

*Energy saving however only comes into play if you can ELIMINATE some other form of flow control that is wasting energy, the savings come from reducing that waste. So if for example you have a 15HP centrifugal pump and you have a throttling valve to control flow (or pressure), then using the VFD speed change to control that will reduce the energy wasted across the throttling valve. It's a common misconception that just using a VFD to reduce speed will save on energy.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[ScusaMe]

.....control 15HP pump motor with reversible contactors and overloads.

H-m-m-m. What kind of pump (Centrifugal or Positive Displacement) and what is the application that requires the pump to be run in reverse ?

How do you control the pump using the overloads ?

Seems there's more here than meets the eye.