VFD or Softstart Requirements 25 HP 460 volt 3 phase motors

[Fordean]

Is their a rule of thumb on softstarts or VFD devices. When do you begin to considered these items. And which would be more preferable. These are to be used in Boiler Recirculation Heat pumps.

I am worried about inrush currents. Nusiance.

Any input. would be appreciated. And lowest cost size of a item.

 

[petersonra]

Is their a rule of thumb on softstarts or VFD devices. When do you begin to considered these items. And which would be more preferable. These are to be used in Boiler Recirculation Heat pumps.

I am worried about inrush currents. Nusiance.

Any input. would be appreciated. And lowest cost size of a item.

I would not worry all that much about inrush on a smallish motor like this in this kind of application.

To me VFDs are a good choice where being able to change the speed of the motor is desirable. They are an expensive soft starter if all you want to do is reduce the inrush.

 

[Besoeker]

Is their a rule of thumb on softstarts or VFD devices. When do you begin to considered these items. And which would be more preferable. These are to be used in Boiler Recirculation Heat pumps.

I am worried about inrush currents. Nusiance.

Any input. would be appreciated. And lowest cost size of a item.

I'm with petersonra.
Unless you have to change the speed or could get energy savings by doing so a VFD is not right for the application.
And, unless your supply is weak or of limited capacity I think it would be hard to justify a soft-start.

 

[Fordean]

I'm with petersonra.
Unless you have to change the speed or could get energy savings by doing so a VFD is not right for the application.
And, unless your supply is weak or of limited capacity I think it would be hard to justify a soft-start.

Ok thanks. Sounds like a good answer.

 

[Fordean]

I would not worry all that much about inrush on a smallish motor like this in this kind of application.

To me VFDs are a good choice where being able to change the speed of the motor is desirable. They are an expensive soft starter if all you want to do is reduce the inrush.

Thanks. No budget for it. Probably runs like 8000 or so?

 

[petersonra]

Thanks. No budget for it. Probably runs like 8000 or so?

for a 25HP drive?

not unless it is gold plated. more like $2000.

depends a lot on brand and model number. and how well your salesman likes you.

 

[weressl]

I would not worry all that much about inrush on a smallish motor like this in this kind of application.

I wouldn't be able to say that without knowing what the incoming service is.

 

[Cow]

It depends on what your doing to know whether or not you need a vfd or soft start. As well as how your incoming service will handle it. There is no general rule of thumb that covers everything across the board. I've seen across the line starters from 0-350 HP and drives/softstarts from 0-500+ HP.

 

[Jraef]

Your local utility will have published rules as to when you have to provide reduced voltage starting to limit starting current, but even though the rules will tell you a HP value, it also will depend on the duty cycle. Usually unless the grid in your area is fairly loaded already, they tend to start at the equivalent of around 50HP at 480V, but I have seen as low as 15HP (Seattle City Light was like that when I lived there). But you can also request a variance if you think you deserve it. I did for our shop because we had an overhead crane that had 20HP motors on it, but we only used it once or twice per month, so we got the variance. Boiler feed recirc pumps may run for a long time each time they turn on, so if your limit is 25HP or less, they may qualify for a variance too.

But as to the VFD, if your pumps run full speed and there is a throttling valve to vary the flow, then the VFD will replace that system and probably pay for itself in energy savings in 2 years or less. If it runs full speed and the flow does NOT vary, then a VFD will WASTE energy in the losses of the drive itself. So in other words, it is entirely application dependent.

 

[petersonra]

I have not run across any utilities requiring something as small as a 25Hp motor on a 480V service that has to have some kind of reduced voltage starting.

 

[Jraef]

I have not run across any utilities requiring something as small as a 25Hp motor on a 480V service that has to have some kind of reduced voltage starting.

Like I said, Seattle City Light was (and apparently is still) 15HP. It's not too hard to get a variance, but this is the default starting point and those who don't ask don't get one.

From SCL's website:

Starting Limitations on Poly-Phase Motors
Across-the-line starting of 15- horsepower motors or less will normally be permitted for starting currents less
than values in Table 12-3. Reduced starting current shall be required on all motors exceeding 15-horsepower
nameplate rating, or motors started more frequently than one start per hour, unless otherwise agreed by SCL.

But it's often stated as a starting kVA value, not HP, but if you look at the motor starting kVA codes and go backward from there, it works out to HP values.