New Grain Bins with Leg How to size the service

[legacyelectric]

Hello everyone: I've been a long time member but only now am I posting: I have an opportunity to bid a new grain bin facility for a private party. The private party want's me to calculate the load to determine the size of the service needed. The power company will be bringing in a 300kva 480v delta-delta transformer. There is going to be (2) 40hp 480v fans per bin (total 4 bins) using soft starts on them. (4) unloading augers 20 hp 480v each. (8) 2hp 480v roof top fans. (1) 25hp 480v motor and finally the 100hp 480v motor at the top of the leg.

There will be a need for a 25kva 480v - 120/240 transformer to power some 120 volt items, less than 75amps

so to recap I want to figure out the size of the service.

8 40hp 480 volt motors
4 20 hp 480 volt motors
8 2 hp 480 volt motors
1 25 hp 480 volt motor
1 100hp 480 volt motor

So looks like 541 total hp

I see there is a code section about farm load calculations in Article 220 Part v

Any ideas would be appreciated.

Thanks in advance.

 

[ptonsparky]

Hello everyone: I've been a long time member but only now am I posting: I have an opportunity to bid a new grain bin facility for a private party. The private party want's me to calculate the load to determine the size of the service needed. The power company will be bringing in a 300kva 480v delta-delta transformer. There is going to be (2) 40hp 480v fans per bin (total 4 bins) using soft starts on them. (4) unloading augers 20 hp 480v each. (8) 2hp 480v roof top fans. (1) 25hp 480v motor and finally the 100hp 480v motor at the top of the leg.

There will be a need for a 25kva 480v - 120/240 transformer to power some 120 volt items, less than 75amps

so to recap I want to figure out the size of the service.

8 40hp 480 volt motors
4 20 hp 480 volt motors
8 2 hp 480 volt motors
1 25 hp 480 volt motor
1 100hp 480 volt motor

So looks like 541 total hp

I see there is a code section about farm load calculations in Article 220 Part v

Any ideas would be appreciated.

Thanks in advance.

Figue the fans will all run at the same time. You and the owner will have to decide when the leg runs with which auger motors or how many. We don’t know your setup. Typical unload is one bin at a time but having the ability to blend product from different bins is a plus. Sounds like a fun project. Enjoy.

 

[ptonsparky]

Is there a particular reason they went with Delta secondary?

 

[legacyelectric]

Is there a particular reason they went with Delta secondary?

I have no idea. They do what they want

 

[kwired]

Is there a particular reason they went with Delta secondary?

Oddball unit they ended up with for "whatever" reason and they want to get rid of it?

This does effect the ability to use 277/480 volt breakers and puts you into needing to use 480 only or even 600 volt breakers.

But then with that many 20+ hp motors one may be looking into something like I-Line panels anyway - if they all come from same panel.

But yes I also agree with the fact that all fans definitely will run at same time, so you at least need to account for all the fans as one major portion of the load. Some cases the fan load is the max load you may ever see, but with a leg, it plus any additional conveyors used for filling may be in addition to all the fans going at once. Seldom do you see loading and unloading loads at same time on the farm though, but if it is a commercial elevator or other storage bins for a plant that processes the contents of those bins, that may have completely different loading characteristics than typical on the farm storage sites.

 

[texie]

I have no idea. They do what they want

What flavor of 480 delta is the service? Is this a 480/240 center tapped arrangement? Or if this is a corner grounded system that is going to complicate things.
I ask as anything other than a 480Y is so rare today. The only time in recent years I've seen any POCO provide anything but a Y service is when they have only 2 phases of a Y system available on the primary.

 

[kwired]

What flavor of 480 delta is the service? Is this a 480/240 center tapped arrangement? Or if this is a corner grounded system that is going to complicate things.
I ask as anything other than a 480Y is so rare today. The only time in recent years I've seen any POCO provide anything but a Y service is when they have only 2 phases of a Y system available on the primary.

What is complicated other than for those that can't grasp the concept of grounding a "phase conductor"?

Neither one can use 277/480 volt rated breakers unless they are supplying a single phase load and avoid using the high leg.

 

[ptonsparky]

... The only time in recent years I've seen any POCO provide anything but a Y service is when they have only 2 phases of a Y system available on the primary.

That is the only time I’ve seen it and that was at least 15 years ago.

 

[texie]

That is the only time I’ve seen it and that was at least 15 years ago.

Yep, rare indeed these days. I had a situation a few years ago that had a 480/240 service that they needed to make bigger. The POCO said no way-if you want to add load we require you to make it a Y service. The POCO made the customer pay for running the 3rd phase almost a mile and rebuild the entire service.
Been my experience that the more rural coops are much more flexible on this than the large investor owned folks. But even that flexibility is fading fast.

 

[kwired]

Originally Posted by texie
... The only time in recent years I've seen any POCO provide anything but a Y service is when they have only 2 phases of a Y system available on the primary.

That is the only time I’ve seen it and that was at least 15 years ago.

My experiences are for a padmount transformer they will prefer wye secondary because those are more common and usually less cost as well. I have run into a few cases where we want to keep existing delta secondary (usually on 120/240) but we are adding load and need a larger transformer - then they will order a padmount with delta secondary. Otherwise delta secondary from pole top banks of single phase transformers are still common. 480 volt delta does seem to be limited to open delta for the most part though for new services. Most POCO's around here still build 120/240 delta banks if that is what is desired.

 

[mayanees]

480V, 800 Amp

480V, 800 Amp

That looks like 480V, 800 Amp gear. And it also looks like the 300 kVA transformer is undersized, especially if all of the fan motors run together. Of course the Utility can easily swap it out with a 500kVA if in fact all of the fans run together.
Ideally you should get the Utility's contribution at the service point and have someone look at the voltage levels to make sure everything can start. VFDs on the fans will help, but if the 100 HP motor is across-the-line started and all of the fans are running there could be voltage drop issues.
Good luck. Nice project.

 

[ptonsparky]

The POCO transformer does seem a bit light for known minimum 440 amp load, but that is typical POCO.

 

[legacyelectric]

The POCO transformer does seem a bit light for known minimum 440 amp load, but that is typical POCO.

I will say this... the Power company is only sizing the transformer to the current load demand. Meaning only two bins will be put up and no leg, for now. This is a 10 year projected plan the farmer has.

I only know about the transformer from the farmer and he only knew the power company said their transformer would put out 360 amps. So based off that I figured it was a delta-delta. Maybe I'm wrong.

 

[SceneryDriver]

What is complicated other than for those that can't grasp the concept of grounding a "phase conductor

Soft starters may have issues with corner-grounded delta power. Most soft starters (and many VFD's, though I know they wern't mentioned here) expect and require wye-connected power. Some may be able to be field-modified by removing the MOV networks from their inputs (AB has several drive lines that jraef has mentioned in other threads) but not all can. The rest of the world uses only solidly grounded wye-connected power, so most equipment is engineered for it and not necessarily so for delta power of any flavor.



SceneryDriver

 

[Jraef]

Soft starters may have issues with corner-grounded delta power. Most soft starters (and many VFD's, though I know they wern't mentioned here) expect and require wye-connected power. Some may be able to be field-modified by removing the MOV networks from their inputs (AB has several drive lines that jraef has mentioned in other threads) but not all can. The rest of the world uses only solidly grounded wye-connected power, so most equipment is engineered for it and not necessarily so for delta power of any flavor.

SceneryDriver

Delta systems and VFDs are bad news. Any ground fault on the delta system runs a risk of damaging the VFDs (the same is true for 3 phase UPS systems and low-end soft starters). If you remove the ground reference jumper (in VFDs that allow that) to keep the protection components (MOVs, CM capacitors) from damaging the rest of the VFD, you also lose some of the protection they provided.

The reason people used to like using ungrounded delta systems was because it provided for an increased ability to keep the entire facility operating in the event of a grounded fault somewhere on the system, because the delta system would essentially go from ungrounded to corner grounded and the main breakers would not trip. But the NEC now requires that you use a corner grounded delta system, or have a ground fault monitoring system, which presumes there is someone there to see that and know what it means. So generally, AHJs will require corner grounding if it's a facility that is "not under engineering supervision". Having a corner grounded delta system then defeats the only valid reason for having a delta system in the first place. Combined with the risk to power electronics, you are better off with a 480Y277V system, even if you never use the 277V. In a lot of industrial plants they just ground the neutral point at the transformer or SE point and never run the neutral wires out to the gear if nothing is using the neutral. That's totally legit and the power electronics will be happy with that.

 

[cpickett]

Delta systems and VFDs are bad news. Any ground fault on the delta system runs a risk of damaging the VFDs (the same is true for 3 phase UPS systems and low-end soft starters). If you remove the ground reference jumper (in VFDs that allow that) to keep the protection components (MOVs, CM capacitors) from damaging the rest of the VFD, you also lose some of the protection they provided.

Does a resistance grounded system pose a risk to drives? If they are worried about uptime, that would be an option, however most likely they would need to be an 'industrial facility under engineering supervision' for an AHJ to be ok with it.

 

[ptonsparky]

Grain storage requires temperature and humidity control. Generally speaking, if one bin needs ventilation, they all do. At over 80,000 bushels per bin, the dockage for poor quality adds up quickly.

Control of when the 100hp starts in relationship to the fans would solve that problem. Leg first, then fans. I’ve seen dampers installed to reduce the back spin as other fans on the bin are started. These fans can take a long time to get moving. Be aware of that.

 

[legacyelectric]

Just got off the phone with the power company. this guy didn't know much but he said it was a 480/277 300kva pad mount transformer

Also where I am located NW Kansas there is no AHJ except for the property owner. No inspections state wide in Kansas except for certain municipalities. Although I want to do it according to code anyway.

Thanks for all the advice, I certainly do appreciate it very much

Larry

 

[kwired]

Just got off the phone with the power company. this guy didn't know much but he said it was a 480/277 300kva pad mount transformer

Also where I am located NW Kansas there is no AHJ except for the property owner. No inspections state wide in Kansas except for certain municipalities. Although I want to do it according to code anyway.

Thanks for all the advice, I certainly do appreciate it very much

Larry

You earlier mentioned this may be a 10 year project. The currently available transformer may be more than needed right now. They may upgrade it when more load is added. I'd still run service conductors according to the final goals.

I've had a few of those kind of sites myself where we start off with one setup, a few years later we add some more, POCO swaps to a larger transformer. My gear was large to begin with so I never needed to change anything, just add my new circuits.

Did one addition to a site last year. Added two more bins, gave POCO the load additions and they decided to upgrade transformer. Am about maxed out on service after this addition, but still have one spare conduit from transformer to service location that can be used for some additional loads, then it becomes a bigger deal if we ever add more after that.

 

[legacyelectric]

You earlier mentioned this may be a 10 year project. The currently available transformer may be more than needed right now. They may upgrade it when more load is added. I'd still run service conductors according to the final goals.

I've had a few of those kind of sites myself where we start off with one setup, a few years later we add some more, POCO swaps to a larger transformer. My gear was large to begin with so I never needed to change anything, just add my new circuits.

Did one addition to a site last year. Added two more bins, gave POCO the load additions and they decided to upgrade transformer. Am about maxed out on service after this addition, but still have one spare conduit from transformer to service location that can be used for some additional loads, then it becomes a bigger deal if we ever add more after that.

Yes that is exactly what the farmer wants to do. build for the future plans and have his equipment already sized for the future plans.