Sizing frequency converter transformer correctly

[powerpete69]

Supplier got back.

Dear powerpete69,

If the voltage is 3 phase 400V, then that is still accepted to supply to this extruder.

But the inverter No. U1 at extruder need to be changed the parameter as below.

P1-09 : Change from 50 to 60 Hz
P1-10 : Change from 1420 to 1705 rpm
See point 5.2 on page 12 in the attached user manual for how to change the inverter parameter.


Looks like I can simply reprogram those two parameters and good to go.
They show you how to reprogram it on page 12 of the guide they included for me.

See how easy that was?
Looks like a $3,000, 480 to 400 three wire to four wire standard transformer will do the trick.

 

[powerpete69]

The manufacturer also said to change the two small inverters in the 2nd machine as well to the same parameters and all will go well.
So now I feel warm and fuzzy about it.
Thanks everyone for your intelligent input.
When I get this hooked up in June or July, I shall let you know how well it works.

 

[powerpete69]

Here's that all familiar and confusing how to size the fuses for your transformer.
The manufacturer does want separate feeds, so I did just that.
They want 250% for the primary protection and 125% for secondary protection in NEC.
480V 3 wire to 400V 4 wire at 45 KVA in case you forgot.
I sized the secondary at 125%, but but went 200% on the primary. Seems like the primary could be lower.
Do I even need the secondary protection?
Also, we have VFD's, not across the line motors.

Any advice on the fuse sizes or wire sizes near transformer or anything else.....most appreciated as this subject confuses most and I could never get a straight answer on it as opinions seem to vary.
See attached drawing.

 

[jim dungar]

I sized the secondary at 125%, but but went 200% on the primary. Seems like the primary could be lower.
Do I even need the secondary protection?
Also, we have VFD's, not across the line motors.

Yes, you need secondary protection whenever your primary protection exceeds 125%.

 

[powerpete69]

Yes, you need secondary protection whenever your primary protection exceeds 125%.

thank you.
So in this case I could just use 70 amp fuse on the primary side and call it a day with a #4 conductor size?
If I just use primary protection, I would size the secondary wire size to the 65 FLA available on the secondary? 65 X 1.25 = 81 amps or #4 wire? Is that correct?

I should know this, but I have been doing more preventative maintenance and less engineering over the last few years.
And yes, I see table 450.3(B) now where it says "primary protection only"......"not required on secondary for 9 amps or more"

 

[powerpete69]

I attached my updated drawing revision 2.

Anyone see any problems?

 

[jim dungar]

thank you.
So in this case I could just use 70 amp fuse on the primary side and call it a day with a #4 conductor size?
If I just use primary protection, I would size the secondary wire size to the 65 FLA available on the secondary? 65 X 1.25 = 81 amps or #4 wire? Is that correct?

The secondary conductors need to be protected per 240.21(C). The primary cannot provide this protection for a wye secondary.

All of your secondary conductors must terminate directly to the transformer terminals, they cannot be spliced as shown on your latest drawing.

 

[powerpete69]

The secondary conductors need to be protected per 240.21(C). The primary cannot provide this protection for a wye secondary.

All of your secondary conductors must terminate directly to the transformer terminals, they cannot be spliced as shown on your latest drawing.

Ok, I see under 240.21 (C) that I need two sets of feeders from the transformer secondary. Check. Got it.

With two sets of #4 feeders from the secondary of the transformer, will the 70 amp fuse on the primary suffice? 450.3(B)
If I'm understanding you correctly, I do not need secondary fuse protection if I use two different secondary feeders without splices.

Thank you very much for your knowledge. Much appreciated.

I attached revision 3. Please let me know if I understood you correctly.

 

[jim dungar]

If I'm understanding you correctly, I do not need secondary fuse protection if I use two different secondary feeders.....

Per 240.21(C) your secondary conductors are limited in length before their required protection. You don't show the length of your #4 feeders, but you would typically be limited to less than 25'.

 

[powerpete69]

Per 240.21(C) your secondary conductors are limited in length before their required protection. You don't show the length of your #4 feeders, but you would typically be limited to less than 25'.

I believe I can keep within 25 feet.
If I do go past 25 feet, I would think an 80 amp fuse on secondary would suffice. 65 FLA X 1.25 = 81.25

I'm probably wrong again....please correct me!

 

[jim dungar]

When using the transformer secondary conductor rules, your conductors can be sized based on their individual protection, so you may not need #4.
If you cannot stay under 25', you may be better off using a single protective device within 25' which feeds your other switches using 240.21(B) similar to your original drawing.

 

[powerpete69]

When using the transformer secondary conductor rules, your conductors can be sized based on their individual protection, so you may not need #4.
If you cannot stay under 25', you may be better off using a single protective device within 25' which feeds your other switches using 240.21(B) similar to your original drawing.

Wow, this is really humbling, but I can take it....at least I'm learning.
So if my loads are greater than 25 feet from transformer, use my original drawing with the splices.....primary and secondary protection. (70 amp primary fuse is probably better)
If I'm less than 25 feet from transformer, then Rev 3 drawing will suffice with the 70 amp primary fuse and separate feeders. (this sounds cheaper)

Did I finally get it right?

 

[jim dungar]

Wow, this is really humbling, but I can take it....at least I'm learning.
So if my loads are greater than 25 feet from transformer, use my original drawing with the splices.....primary and secondary protection. (70 amp primary fuse is probably better)
If I'm less than 25 feet from transformer, then Rev 3 drawing will suffice with the 70 amp primary fuse and separate feeders. (this sounds cheaper)

Did I finally get it right?

Because you have a Wye secondary, what happens on the primary is not important.

You need to have a single protective device on each set of secondary conductors, within 25' of the transformer. These conductors cannot be spliced, or tapped, before the disconnect. This is what is wrong with your drawing showing two conductors on the line side of your first disconnect.

When using the rules in 240.21, conductors do not need to be sized any larger than the protective device in which they terminate. This reduction in conductor size is often cost justified.

If the 25' length is a limiting factor you will need to have a single protective device and then feed to your two smaller switches.

 

[powerpete69]

Because you have a Wye secondary, what happens on the primary is not important.

You need to have a single protective device on each set of secondary conductors, within 25' of the transformer. These conductors cannot be spliced, or tapped, before the disconnect. This is what is wrong with your drawing showing two conductors on the line side of your first disconnect.

When using the rules in 240.21, conductors do not need to be sized any larger than the protective device in which they terminate. This reduction in conductor size is often cost justified.

If the 25' length is a limiting factor you will need to have a single protective device and then feed to your two smaller switches.

Ahhhh, more interesting stuff!!!

Ok, just talked w electrician. The 30 amp and 35 amp fused disconnects will be around 20 feet away from transformer.
With this being the case, I believe my attached rev 3 drawing is then correct.

I believe you are saying I certainly could use #4 wire to the loads from the transformer in this case, but per 240.21 only requires a #10 to the 30 amp fused disconnect from transformer....and a #8 to 35 amp fused disconnect assuming less than 25 feet. (separate feeds)

Now do we have it? I can see why no one can easily explain this. Going thru the tons of exceptions and cross references of the code book is most taxing and complicated!!

 

[jim dungar]

You are getting it.

We have been talking about a specific installation so some details, important to others, may have been omitted. In particular there are sizing minimums when applying certain applying certain parts of 240.21. Also, the lengths mentioned are for the conductors themselves not the physical distance between the devices.

 

[powerpete69]

These European 400V, 50 HZ mini extruders did finally get wired up and running in Northeast Ohio.. About a year later, the electricians were busy! By doing research with company in Indonesia..... I avoided the $30,000 cost of a frequency converter and just installed a 480V to 400V transformer (maybe $1500 ish) and left it at 60 hz. Plus a straight transformer will last way longer than frequency converter.
The key was re-programming the (3) VFD's from 50 to 60 hz and changing the rpm from 1420 to 1705 per manufacturer recommendations. Took 10 minutes to reprogram 3 of them. Easy per the manual.
Works great and the operator couldn't be happier with his two mini extruders.
All's well that ends well.