Sizing a Soft Start for a 100 HP motor for a Hammer Mill

[Cydog]

Good Morning ,

We have a 100 HP , 480 V (Full Load Amps 124 ) Hammer Mill motor that has a Wye/Delta starting procedure. I would like to put a Soft Start on this motor. What is the best way to size up a Soft Start and what are the conditions that need to be considered ?

Thanks so much for your help.

 

[JesperMP]

It depends heavily on the kind of application.
Siemens has a sizing tool that we use:
Simulation Tool for Soft Starters (STS)
I believe that the other big vendors have similar tools or guides.

 

[doctord]

https://benshaw.com/wp-content/uploads/2020/07/White-Paper-Soft-Start-vs-Wye-Delta.pdf
This document gives some good information. I have never used their product so can not recommend.
I like the soft starter or VFD instead of the WYE/DELTA start. Replaced many starters on German equipment as they were not sized to last.

 

[Gene Bond]

Use a heavy duty rating, something that will give you 450% FLA or so for ramping. A hammer mill is high inertia, so a fairly long starting time.

I like the Motortronics soft starters, personally: https://www.motortronics.com/pages/lowvoltage_VMX2.html Have used them for many years on all types of crushers, grinders, etc.

 

[ndzied1]

Make sure you are aware of the limited number of starts per hour for soft starters.

If not followed, bad things can happen ( one cheap soft starter we used once caught fire. That was not a good day).

 

[Cydog]

Thanks everyone . I'm looking at a WEG . Yes I agree going with a much larger Soft Start for that reason. I need to measure the space for it.

 

[jraef]

One major thing to be wary of is whether or not it has SCRs on 3 phases. Cheap soft starters use only 2 phases, the third phase is a bus bar. This is OK for some pumps and fans, but would be bad to use on something like a hammer mill. Don’t let anyone talk you into it either. It’s bad for the motor and has an increased risk of causing serious damage.

Stick to what Gene Bond said; heavy duty rating, stick to a major brand. I used to work for Motortronics 20 years ago and Weg came to us to build their starters in the US, so I’ve seen them from the inside, I was not impressed. to me the best are AB, Motortronics, Benshaw, Siemens (beware of their 2 phase option though) and maybe ABB. Schneider and Eaton are not good for something Ike this IMHO.

 

[sbaum]

I can recommend Benshaw Severe Duty series (RB2/RB3). They are solid and support is great. I have personally installed one on a 125HP hammermill.

 

[ndzied1]

One major thing to be wary of is whether or not it has SCRs on 3 phases. Cheap soft starters use only 2 phases, the third phase is a bus bar. This is OK for some pumps and fans, but would be bad to use on something like a hammer mill. Don’t let anyone talk you into it either. It’s bad for the motor and has an increased risk of causing serious damage.

The soft starter I alluded to earlier that caught fire was one of these 2 phase jobs. We ended up replacing it with an AB with 3 phases and it has worked well since.

 

[Levi G]

Have you considered using a VFD instead? I am working on installing a VFD on a 20hp hammer mill these days.
The reason for a vfd is so the mill can run at a slower speed. I have been told that the grain quality coming out at the slower speed is more uniform with less of the grain being turned into dust.
As far as I know the throughput will be the same at a slower speed.

 

[Gene Bond]

A VFD can give some significant bennefits on these and similar machines. Things like long, soft starting times without using excess power (possibly reducing demand charges and motor heat). As well as slightly tuning the speed for a more desirable finished particle size, etc.

I've done this on hammers, impactors, and grinders.

 

[p8p8]

A VFD can give some significant bennefits on these and similar machines. Things like long, soft starting times without using excess power (possibly reducing demand charges and motor heat). As well as slightly tuning the speed for a more desirable finished particle size, etc.

I've done this on hammers, impactors, and grinders.

VFD is way better.
But price difference:
https://www.automationdirect.com/ad...ge_ms="208-460 VAC"&Amperage_Rating_ms="192A"

https://www.automationdirect.com/ad...s=10&Nominal_Drive_Input_Voltage_ms="460 VAC"

 

[sbaum]

Best to know your application and load before saying a VFD is better than a Softstart. In the cases mentioned for smaller loads, I agree.
The 125HP hammerill I refered to is essentially a wood chipper. That is a severely abusive load (at least this customer certainly abuses his ) with high current spikes. I'm certain a VFD would have failed long ago for this applicaiton. The softstart has built-in bypass so can better withstand the high current spikes after it's up to speed

 

[Cydog]

Thanks for all your input. This plant is very abusive on equipment. Another question I have is , what do they mean when they say 3 Starts an Hour , 10 Starts an Hour , etc. ? Is this due to the time needed to charge the capacitors ?

Thanks again,

 

[Gene Bond]

No, it is time to dissipate the heat from the starting current.