Transformer w/ 240V Delta Secondary

[Fitzdrew516]

There is a piece of equipment that the manufacturer SPECIFICALLY lists that they need a 220V 3ph supply. It was designed with a 240V 3ph supply (Square D 75 KVA transformer 480/240 delta Catalog #EE75T6HCU) to a panel and then the panel feeds a couple of these pieces of equipment. It was designed that way because we were told it needed 240v and it was the best guess we had at the time (owner needed drawings out before equipment was final). We tried to push back, but to no avail.

Anyway - Question being can the taps on the secondary of the transformer be changed to get to the 220V that I apparently need now? I'm doubting that it can be done, but I figured I'd ask before we tell them they're going to need to buck down to 220.

From the manufacturer -

"The Multivac can handle temporary fluctuations within 10%. However, if you cannot maintain a nominal 220 Volts, further action is required (208 Volt nominal supply is not an acceptable supply). "

Thanks,
-Drew

 

[dkidd]

Anyway - Question being can the taps on the secondary of the transformer be changed to get to the 220V that I apparently need now? I'm doubting that it can be done, but I figured I'd ask before we tell them they're going to need to buck down to 220.

What do the nameplate/instructions say?

 

[Fitzdrew516]

What do the nameplate/instructions say?

The full quote is

"Multivac machines are designed to operate on a nominal 220 Volt, 3 phase power system unless otherwise specified. The power should be a separate service line to assure clean, non-fluctuating power. No neutral conductor is required; however, a good earth ground conductor is essential. The supply voltage must not fluctuate outside 220 VAC +/- 10%. You should monitor your voltage during both heavy and light load times of the day to ensure fluctuations do not exceed 10%. The Multivac can handle temporary fluctuations within 10%. However, if you cannot maintain a nominal 220 Volts, further action is required (208 Volt nominal supply is not an acceptable supply). Voltages that fall outside of this range will require a “Buck” or “Boost” transformer to bring the voltage into an acceptable range. Multivac can furnish you with transformer information upon request."

 

[jeremy.zinkofsky]

Look at the nameplate on the XFMR for the tap settings that are desirable. If that information is not provided, call the manufacturer of the XFMR. If you cannot get the voltage you want you will have to get a buck XFMR from the equipment manufacturer. Those are your only two options.

 

[Jraef]

Wow, that is a STUPID design spec if you ask me. I know that's not your issue, I'm just commenting.



That Sq D part number doesn't come up as valid, maybe because it's old now. But the one they sell now, with the middle of the part number being 151, shows 2 x 5% center taps. That means the second tap gives you 10% lower than the normal 240V secondary which would be 216V. But also remember, that is based on the primary voltage so it's a ratio, not an absolute value.

 

[Fitzdrew516]

Wow, that is a STUPID design spec if you ask me. I know that's not your issue, I'm just commenting.



That Sq D part number doesn't come up as valid, maybe because it's old now. But the one they sell now, with the middle of the part number being 151, shows 2 x 5% center taps. That means the second tap gives you 10% lower than the normal 240V secondary which would be 216V. But also remember, that is based on the primary voltage so it's a ratio, not an absolute value.

Here's a picture of what was submitted - Does this help?
Forgive my ignorance, but I don't know what "2-2.5% FCAN" or "4-2.5%FCBN" means. Can anyone shed light on that?

 

[kwired]

Here's a picture of what was submitted - Does this help?
Forgive my ignorance, but I don't know what "2-2.5% FCAN" or "4-2.5%FCBN" means. Can anyone shed light on that?

The transformer has multiple taps to compensate for variances in primary voltage. The chart on that sheet tells you if the primary voltage is 480 volts then connection to tap #3 (which is usually the default tap from the factory) will yield nameplate output secondary voltage (of 240).

If your primary voltage were 492 then you connect tap #2 to get output of 240.

What is being said is you can adjust these taps to get as close as possible to desired output depending on what actual primary voltage is.

 

[jumper]

Forgive my ignorance, but I don't know what "2-2.5% FCAN" or "4-2.5%FCBN" means. Can anyone shed light on that?

FCAN stands for ``Full Capacity Above Nominal``
FCBN stands for ``Full Capacity Below Nominal``

For example: If a Transformer has 2 - 5% FCBN taps and the nominal voltage is 240 volts, then there are two taps below 240 volts in 5% increments. 5% of 240 is 12 volts, thus there is are taps for 228 and 216 volts. Since kVA capacity is voltage times current (for single phase; for three phase also multiply by 1.732 (the square root of 3),) the fact that the tap can handle the full capacity of the transformer in kVA, means that the tap can handle enough current for the Transformer to provide the nameplate kVA rating with that voltage input.

http://www.schneider-electric.us/en/faqs/FA101575/

 

[Fitzdrew516]

Thanks, Jumper and kwired. That's helpful. I knew it had something to do with that, but wasn't sure of the acronym.

I just got off the phone with the manufacturer of the equipment and he said that if it were truly a 240 supply it'd be fine and the close to 230 I could get the better. Here's the deal though... often times the nominal 240 can really be 250V or higher and he said over 240 probably wouldn't be good.

So theoretically since I'm wanting to get close to 220V instead of the transformer's typical output of 240V could you adjust the taps on the primary accordingly? Say my actual voltage is 480 on the primary, well could I adjust the taps and not use the 3rd tap (as suggested on the chart) and the output would be less?

 

[Jraef]

FCAN = Full Capacity Above Normal
FCBN = Full Capacity Below Normal

So 4 x 2-1/2% FCBN means you have 4 taps, each one at 2-1/2% below normal. Ergo if you use the 3rd tap, you will have 7-1/2% below normal voltage, so a 480V input will result in a secondary of 222V.

 

[winnie]

Is the manufacturer okay with corner grounding?

You have a delta secondary, and the manufacturer says 'a good earth ground conductor is essential'. With a delta secondary you don't have a neutral to ground, your picture doesn't even show a phase center tap. So the only ground you can provide is a corner ground or you need an additional grounding transformer.

-Jon

 

[GoldDigger]

FCAN = Full Capacity Above Normal
FCBN = Full Capacity Below Normal

So 4 x 2-1/2% FCBN means you have 4 taps, each one at 2-1/2% below normal. Ergo if you use the 3rd tap, you will have 7-1/2% below normal voltage, so a 480V input will result in a secondary of 222V.

It looks like the tap numbered 3 is the normal one though.
So "third" is not equal to "three", as there are high and low taps either side of "normal"

Your example is fine, it just does not match the OPs situation.

 

[Jraef]

It looks like the tap numbered 3 is the normal one though.
So "third" is not equal to "three", as there are high and low taps either side of "normal"

Your example is fine, it just does not match the OPs situation.

Good catch, I didn't really look that closely at it.

 

[texie]

Is the manufacturer okay with corner grounding?

You have a delta secondary, and the manufacturer says 'a good earth ground conductor is essential'. With a delta secondary you don't have a neutral to ground, your picture doesn't even show a phase center tap. So the only ground you can provide is a corner ground or you need an additional grounding transformer.

-Jon

Yep, caught my eye too. I'd be very surprised if that equipment is built to comply for use on a corner grounded system. Corner grounding brings on a whole host of equipment listing issues for the machine and the equipment in the supply circuit.

 

[GoldDigger]

On the other hand, they may just be asking for a good EGC.
They said "ground", which is ambiguous between " grounded" and "grounding".
It still does not tell us anything for sure about whether ungrounded or corner grounded would be acceptable.
And, of course, it is possible that they are saying that they do not need to use the neutral but expect a center grounded wye anyway.

 

[kwired]

If your nominal 240 runs at about 250, then your nominal 480 is probably running close to 500.

That is typical at places where I work.

208 volt nominal is usually running closer to 215, 277 nominal about 285.

Chances are OP needs to try the #1 tap which is for 504 volts with output of 240. Depending on actual input volts he probably at least ends up below 240 but probably not all the way down to 230.

 

[templdl]

Is this a drve appication? Have you considered a transformer with a 240y/139 secondary? Take a look at the drive transformer catalog section which should include a selection of drive isolaion transformers with wye secondaries. When you ground the X0 you will have 139v to ground which one one think would be preferred rather than corner grounding a delta with 240v to ground.

 

[Jraef]

You don't have to have a corner grounded secondary, but if you don't, you must have fault monitoring and a way to shut it down if one is detected.

I've heard, but have not yet checked, that this would not apply to a single motor if that is the only load.

 

[jeremy.zinkofsky]

Tap 6 will give you 222V on the secondary.

From your post from the manufacturer, it sounds like you just need an EGC via a ground rod or approved means. The manufacturer stated that the equipment does not need a neutral, so the Delta/Delta configuration is fine. You should still confirm that though.

 

[kwired]

Tap 6 will give you 222V on the secondary.

You sure, if input is 444 tap 6 is supposed to give 240 secondary.

Change input to 480 and the secondary will rise proportionally - should get about 259. If input is closer to 500 secondary is going to be even higher.