Looking for some calculation help for a transformer

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We have a job that is a little out of my depth. I am hoping to get some help or a reference to hire someone to do the calculations. The client has a generator for a barge. They are trying to get 240 and 120 for a sub panel.

The power output is 480v Wye. There is one free 50A breaker they want to use as a feed to a connex that will house this panel. The run is about 50 feet. They would like a 15kv transformer. Since they are stepping down the power, and they have that 50ft run, I am unsure what I can give them on the other end. Also I am unsure if the 15kv transformer is going to be big enough for the application. As I said, I do not mind hiring someone to run the calculations, I am just getting a lot of different information from local vendors.


Thanks again,

Phil
 

Smart $

Esteemed Member
Location
Ohio
Is this system entirely on the barge or a shore power system? If former, the NEC does not apply. However, we can still provide some design considerations.

You said 15kv. Assume you mean 15kVA...? Don't know if it's large enough. Depends on what is being powered...? Do they want/need 240/120 3? 4W or 120/240 1? 3W?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
In addition to what Smart $ has asked, I have a few questions of my own:

  1. You say they have a generator. Is that the existing on-board power supply for the barge?
  2. You say the power output is 480V Wye. Do you mean that that is what the generator puts out?
  3. If this is a barge, the power is more likely to be 480V ungrounded delta. Can you confirm?
  4. What is a ?connex??
  5. What do you mean by saying there is one free 50A breaker? Are you saying that the existing on-board distribution system has one available spare breaker, and it is a 50A? If so, then where is it, what is its voltage, and how many poles does it have?
  6. What are the loads that the transformer will serve?

 
Here we go.... The client is a government agency so if your familiar with anything involving the feds. It never works. Secondly the barge is located in a secure area of operations, so I cant send anyone out there to verify. So we are playing a game of telephone trying to get information.

There specs were as follows, think of them more of a suggestion, as they may not fit within the parameters they have.

1. Stainless steel enclosure
2. 15 KVA step down transformer 480V/240, 120 (encapsulated)
3. 2-50 amp single phase 240V weatherproof receptacle
4. 2-20 amp single phase GFI weatherproof receptacle
5. 1-20 amp 3 phase 480V weatherproof receptacle
6. 50 foot power cable SO with 4 conductors #6 AWG
7. Main circuit breaker protection for panel with disconnect handle
8. Single pole circuit breaker protection
9. Double pole circuit breaker protection
10. Unit pre-mounted on unit strut channels ready for wall installation
11. All features pre-tested prior to delivery


Info On The Generator:

Generator suppling power WhisperWatt 150 model number DCA-150US-J2

it is set up as the picture indicates. I am told the following:

"wired with a black wire coming off the U terminal, a Red wire coming off the V terminal, a blue wire coming from the W terminal and nothing on the O terminal. There is a green wire coming from the ground. I spoke with the people that built the system for us, We are 95% sure that it is 480v Wye."

I am told, they have one free breaker, which is 50A. They want to use that to plug this into.

Give me a sec and I will respond to the additional questions.

gen..jpg
 
In addition to what Smart $ has asked, I have a few questions of my own:

  1. You say they have a generator. Is that the existing on-board power supply for the barge?
  2. You say the power output is 480V Wye. Do you mean that that is what the generator puts out?
  3. If this is a barge, the power is more likely to be 480V ungrounded delta. Can you confirm?
  4. What is a ?connex??
  5. What do you mean by saying there is one free 50A breaker? Are you saying that the existing on-board distribution system has one available spare breaker, and it is a 50A? If so, then where is it, what is its voltage, and how many poles does it have?
  6. What are the loads that the transformer will serve?




  1. You say they have a generator. Is that the existing on-board power supply for the barge?
Yes it powers the barge.



  1. You say the power output is 480V Wye. Do you mean that that is what the generator puts out?
This is what they are saying.



  1. If this is a barge, the power is more likely to be 480V ungrounded delta. Can you confirm?
Could be, again, I have limited information



  1. What is a ?connex??
A connex is a steel storage container, like a shipping container



  1. What do you mean by saying there is one free 50A breaker? Are you saying that the existing on-board distribution system has one available spare breaker, and it is a 50A? If so, then where is it, what is its voltage, and how many poles does it have?
Yes one free breaker, 50 feet from where this will be mounted. Yes it is 50A, the voltage is 480v 4 wire, so I am told. I can try to get some more information.



  1. What are the loads that the transformer will serve? Serves a couple of Air compressors, and just some std. power (tool chargers ext.)
 
Is this system entirely on the barge or a shore power system? If former, the NEC does not apply. However, we can still provide some design considerations.

You said 15kv. Assume you mean 15kVA...? Don't know if it's large enough. Depends on what is being powered...? Do they want/need 240/120 3? 4W or 120/240 1? 3W?

My mistake, yea 15kva, NEC does not apply. I am not sure what they really need, nothing they will be running is 3 phase, most demand is for a 240v compressor.
 

Smart $

Esteemed Member
Location
Ohio
2. 15 KVA step down transformer 480V/240, 120 (encapsulated)
3. 2-50 amp single phase 240V weatherproof receptacle
4. 2-20 amp single phase GFI weatherproof receptacle
Still hard to say if 15kVA transformer is sufficiently sized. Output current rating at 120/240V 1? 3W is 62.5A. Spec's only provide receptacles as the "loads". If each receptacle supplies current to its rating (120A total), the xfmr is undersized.
 
Still hard to say if 15kVA transformer is sufficiently sized. Output current rating at 120/240V 1? 3W is 62.5A. Spec's only provide receptacles as the "loads". If each receptacle supplies current to its rating (120A total), the xfmr is undersized.


Thanks, I am thinking of giving them one 30a and one 50a on the 240. I am also concerned on the: 1-20 amp 3 phase 480V weatherproof receptacle. The way I see it this should be its own circut from the main panel. Or perhaps I am being too cautious.
 

Smart $

Esteemed Member
Location
Ohio
...I am told, they have one free breaker, which is 50A. They want to use that to plug this into.

...I am also concerned on the: 1-20 amp 3 phase 480V weatherproof receptacle. The way I see it this should be its own circut from the main panel. Or perhaps I am being too cautious.
The 50A breakers (2-pole) protect the twist-lock receptacles... and they're only for 120/240V 1? output (see Figure 9 on page 39 of the manual: http://www.multiquip.com/multiquip/...rev_0_60_hz_manual_DataId_93408_Version_1.pdf)

To get 480V 3?, they'll have to use the terminal block, which along with the other breakers and receptacles, is protected with both a 400A breaker and an overcurrent relay (page 40).

They're gonna have to re-think what they think they want... :p
 
The 50A breakers (2-pole) protect the twist-lock receptacles... and they're only for 120/240V 1? output (see Figure 9 on page 39 of the manual: http://www.multiquip.com/multiquip/...rev_0_60_hz_manual_DataId_93408_Version_1.pdf)

To get 480V 3?, they'll have to use the terminal block, which along with the other breakers and receptacles, is protected with both a 400A breaker and an overcurrent relay (page 40).

They're gonna have to re-think what they think they want... :p

I believe they are using the terminal block, to there own power distribution box. This is where the other 50A breaker is.
 
So assuming it is 480 WYE, and they are tapping off of a 50A breaker on its own distribution box, I would only need a 1 5KVA, 240 X 480-120/240 Volt 1 Phase Transformer? Since the feed on the other end is only 1P I could just use two of the leads?


Thanks again,
Phil
 

Smart $

Esteemed Member
Location
Ohio
So assuming it is 480 WYE, and they are tapping off of a 50A breaker on its own distribution box, I would only need a 1 5KVA, 240 X 480-120/240 Volt 1 Phase Transformer? Since the feed on the other end is only 1P I could just use two of the leads?

Thanks again,
Phil
That's correct... but what about the 20A 480V 3? receptacle? Need all three hots for that.
 
well if they have to have it, I would think I would need to run a small 3 phase sub panel over just for that and the transformer feed. I do not think It is a good idea, seems like too much run, to little power and if I am not mistaken I think generators start to do odd things when you pull to much from one side or breaker. They would be operating at the max amps (30A for the transformer and 20A for the outlet) not sure if the distance matters, but they want 6/4 wire, I just see someone plugging in all sorts of stuff due to convenience when they are prob. better off grabbing it off of another circuit. What do you think Smart $ and thanks again for your help.
 

Smart $

Esteemed Member
Location
Ohio
well if they have to have it, I would think I would need to run a small 3 phase sub panel over just for that and the transformer feed. I do not think It is a good idea, seems like too much run, to little power and if I am not mistaken I think generators start to do odd things when you pull to much from one side or breaker. They would be operating at the max amps (30A for the transformer and 20A for the outlet) not sure if the distance matters, but they want 6/4 wire, I just see someone plugging in all sorts of stuff due to convenience when they are prob. better off grabbing it off of another circuit. What do you think Smart $ and thanks again for your help.
Well, IMO, there's nothing wrong with giving them both the 480V receptacle and powering the transformer with the 6/4 SO... provided each has proper ocpd in the SS enclosure. Kind of hard to make a load assessment when all you are supplying is receptacles...!!!
 
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