Step Up Transformer
- Thread starter wireddd
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Step Up Transformer
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- <font size="2" face="Verdana, Helvetica, sans-serif">1. Buy an uninterruptible power supply sized for that one load only.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">2. Buy a motor generator with a 208V input and a 240V output.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">3. Buy a different load that accomplishes the same mission, but uses 208V.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">4. Determine whether the load you have is dual-rated (i.e., can handle the 208V).</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">5. Don?t tell the customer (what do they know about voltage anyway?), and make sure you cash the check before the load burns up.
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john m. caloggero
Senior Member
Re: Step Up Transformer
First of all we have not been told the rating of the load. Is it a 3-phase, 240/138 volt european equipment and is the neutral necessary? If the neutral is not needed, I believe the least expensive method to solve the 3-phase, 208V to 240V problem is to buy two single-phase transformers rated 208v primary and 32v secondary. Connect them in an open delta 3-phase boost configuration so that the input 208v plus the secondary 32v are additive and will provide 3-phase 240V without a neutral.
However, if a neutal is needed, you will have to use 3 single-phase, 208v primary with 32v secondary transformers connected in WYE to provide 3-phase and develop a 138 volt neutral.
First of all we have not been told the rating of the load. Is it a 3-phase, 240/138 volt european equipment and is the neutral necessary? If the neutral is not needed, I believe the least expensive method to solve the 3-phase, 208V to 240V problem is to buy two single-phase transformers rated 208v primary and 32v secondary. Connect them in an open delta 3-phase boost configuration so that the input 208v plus the secondary 32v are additive and will provide 3-phase 240V without a neutral.
However, if a neutal is needed, you will have to use 3 single-phase, 208v primary with 32v secondary transformers connected in WYE to provide 3-phase and develop a 138 volt neutral.
john m. caloggero
Senior Member
Re: Step Up Transformer
wiredd: The buck-boost method is the most efficient as far as cost is concerned, because the KVA rating is based on the amount of current in the 32V secondary, based on the load current. Example: if the load current is 15 amps, 3-phase, three 5 Kva transformers can be connected WYE and provide the power. Remember that the current will be higher on the 208v input, approximately 17.3A. You don't get something for nothing.
wiredd: The buck-boost method is the most efficient as far as cost is concerned, because the KVA rating is based on the amount of current in the 32V secondary, based on the load current. Example: if the load current is 15 amps, 3-phase, three 5 Kva transformers can be connected WYE and provide the power. Remember that the current will be higher on the 208v input, approximately 17.3A. You don't get something for nothing.
Re: Step Up Transformer
John,
It was interesting to read your replies. I had a reply with regard to applying a B-B transformer or a 208v delta- 240/133 wye(commonly available with drive isolation transformers)all typed up to answer this post before you responded but deleted it due to the lack if application information provided by the poster.
But there are a couple of my additional thoughts and a blind shot at his application:
He could also use a common 240-208y120 as a step-up for 240v and address the 120 with an individual 240-120/240 1ph transformer for those loads instead of attempting to use a 208-240/120 which is not common. Or, it may be possible to use (3) standard 208-120/240 1ph transformers in a delta and take only (1) phase-phase center tap(neutral point) on one of the transformers for the 120v and disregard the center taps of the other two after assuring that those taps are not bonded to the enclosure and are insulated and isolated.
It is intriguing to me why so much relevant information is commonly omitted when asking a question.
Dave
John,
It was interesting to read your replies. I had a reply with regard to applying a B-B transformer or a 208v delta- 240/133 wye(commonly available with drive isolation transformers)all typed up to answer this post before you responded but deleted it due to the lack if application information provided by the poster.
But there are a couple of my additional thoughts and a blind shot at his application:
He could also use a common 240-208y120 as a step-up for 240v and address the 120 with an individual 240-120/240 1ph transformer for those loads instead of attempting to use a 208-240/120 which is not common. Or, it may be possible to use (3) standard 208-120/240 1ph transformers in a delta and take only (1) phase-phase center tap(neutral point) on one of the transformers for the 120v and disregard the center taps of the other two after assuring that those taps are not bonded to the enclosure and are insulated and isolated.
It is intriguing to me why so much relevant information is commonly omitted when asking a question.
Dave
Re: Step Up Transformer
Spoke with Acme Electric Corp engineers today. Cheapest and simplest way is to use three boost transformers and carry the neutral through from the primary 208 volt side. On thier wiring diagrams it is picture AA. Using the 12/24 buck boost unit this will give me about 230 volts with a neutral. All within the limits for a 240 volt motor and accessories that the customer has.
Thanks for all of your help, some very interesting answers.
Spoke with Acme Electric Corp engineers today. Cheapest and simplest way is to use three boost transformers and carry the neutral through from the primary 208 volt side. On thier wiring diagrams it is picture AA. Using the 12/24 buck boost unit this will give me about 230 volts with a neutral. All within the limits for a 240 volt motor and accessories that the customer has.
Thanks for all of your help, some very interesting answers.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Step Up Transformer
16/32 are available, I wounder why they want to use 3? I have done this with just 2 many times.
16/32 are available, I wounder why they want to use 3? I have done this with just 2 many times.
- Location
- Massachusetts
Re: Step Up Transformer
Straight 3 phase I have always done it with just two.
Off the top of my head I think because he needs a neutral.Originally posted by hurk27:
16/32 are available, I wounder why they want to use 3? I have done this with just 2 many times.
Straight 3 phase I have always done it with just two.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Step Up Transformer
Here is a tool that you can use to determine which one you need. You can get as close as 236 volts. All you have to do is put in the KVA or circuit amperage and hit enter:
Square D Buck/Boost selector
P.S. use the 13.3% setting for 240 volts output
[ April 19, 2005, 07:12 PM: Message edited by: hurk27 ]
Here is a tool that you can use to determine which one you need. You can get as close as 236 volts. All you have to do is put in the KVA or circuit amperage and hit enter:
Square D Buck/Boost selector
P.S. use the 13.3% setting for 240 volts output
[ April 19, 2005, 07:12 PM: Message edited by: hurk27 ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Step Up Transformer
I never thought about the neutral as I dont remember when I have ever boosted a whole panel. and when I do a machine I do just the 3? loads. Why boost the 120 volt? It just cost more.
I never thought about the neutral as I dont remember when I have ever boosted a whole panel. and when I do a machine I do just the 3? loads. Why boost the 120 volt? It just cost more.
john m. caloggero
Senior Member
Re: Step Up Transformer
Hi Dave, It is less expensive to use a buck-boost transformer configuration. Why spend the money for standard type transformers that would require a greater KVA rating than the buck-boost transformer.
Hi Dave, It is less expensive to use a buck-boost transformer configuration. Why spend the money for standard type transformers that would require a greater KVA rating than the buck-boost transformer.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Step Up Transformer
Hi Dave the link I posted above will size the transformer for you if KVA is known. And yes Buck-boost is not the way to go when your trying to overcome voltage drop and if you have a varying load. As when the load drops off, the transformer will still do what it's supposed to do, "boost". you will wind up with over voltage.
Hi Dave the link I posted above will size the transformer for you if KVA is known. And yes Buck-boost is not the way to go when your trying to overcome voltage drop and if you have a varying load. As when the load drops off, the transformer will still do what it's supposed to do, "boost". you will wind up with over voltage.
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