Transformer Question

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  #1  
Old 05-18-06, 10:13 AM
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Transformer Question

If my transformer taps are set for 120/208 volts, 3 phase, but I need to run at 230 volts, 3 phase for my hoist, I obviously must install a step-up transformer for the 230volts right? There is now way to run another secondary back to the 120/208volt, 3 phase transformer since the taps can only be set for all secondaries comming off of that transformer, right?

Today at my office a squirrel took the power to everone's office but mine. The electricians did not enter the electrical room, only did something to the transformers on top of the pole. I assume the squirrel got his little mouth on one phase and his tail on the other phase (since they found his body parts) knocking out the cut-out fuses on top of the power pole for two phases (two pots), but the squirrel left a phase hot. That hot phase was on a subpanel feeding off of the 3 phase main distribution panel where the subanel then fed my sole office in return, correct?
 
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  #2  
Old 05-18-06, 11:02 AM
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Originally Posted by eeee
If my transformer taps are set for 120/208 volts, 3 phase, but I need to run at 230 volts, 3 phase for my hoist, I obviously must install a step-up transformer for the 230volts right? There is now way to run another secondary back to the 120/208volt, 3 phase transformer since the taps can only be set for all secondaries comming off of that transformer, right?
First check to see if 208V is an acceptable voltage for the motor; many are rated 208-240V. 240V three-phase is an odd configuration and perhaps a misprint in some documention. Maybe call the manufacturer or look up the info online.

I assume the squirrel got his little mouth on one phase...
A likely scenario, yes.
 
  #3  
Old 05-18-06, 05:40 PM
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transformer

See if you have the method for 120/240volt secondary. There should be a schematic of the transformer and it's terminating points on the front Find the numbers for 240 volt and change your connections. Make sure your power is disconnected at the disco. Also the issue with the squirrel might have been contained to that specific area by blowing fuses to prevent it from further danger and damage.
 
  #4  
Old 05-18-06, 06:07 PM
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Check the motor

Take a look at the motor and see if it is a multi-tap. I don't know what the motor looks like but just a hunch. In some types of commercial equipment they'll have a multi-tap type connections for the motor which, with the correct connections in number sequence, they can operate at different voltages, check with mfg, to be sure.
 
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Old 05-18-06, 08:23 PM
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Actually voltage requirements for motors are +/- 10% of nameplate rating. Although a 230 v rated motor is actually designed to be run on 240 volts, 208 is (marginally)acceptable (230*.9=207) although higher would be better. Check your actual voltage to be sure you actually have 208 as well. If voltage is typically low in your area, you could reach the point of damage. If you are lucky, the poco runs your taps on the high side and maybe end up around 213 volts.

Check current draw after hooking it up.

The other thing you may check is if the motor has a choice of wye or delta configurations. Post back if this is available.

While ibpooks is correct as to 240 3 phase being odd, it is not unheard of.

Where I live there are several different 3 phase supply voltage configurations.
There is what you have which is a wye configuration (the lower standard voltage of this config. the higher would be 277/480)

grounded delta 120/240 and 240/480 but with one leg grounded so if reading voltages to ground you have two with voltage and one that reads 0 but you still get 240 (low) or 480 (high) from leg to leg

ungrounded delta 240 only and higher setup 480 only. That would be read from any leg to ground or leg to leg.

center tap (or high leg) delta 120/240 but one of the legs to ground reads ~208-215. but still have 240 from any leg to another leg

It all depends what the poco has to the area. Most newer systems are the 120/280 and 277/480 wye config.

These are in addition to the single phase (residential) supply. (two legs each 120 to ground and 240 leg to leg.

re: the squirrel situation:

it is very unusual to take only one leg to a panel. Chances are you have at least 2 legs (sometimes done with the high leg system described above) or all three to the panel that feeds your office but only noticed what was off and not what may have been on.

What the poco did was to replace the fuses in the cut outs. That is why they are there, to protect the wires going into the buiding and their equpment. Sounds like they worked like they are supposed to if this is all they did to get you up and running.
 
  #6  
Old 05-19-06, 05:06 AM
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Mucking with the taps on your service transformer is not a DIY job.

Transformer taps are placed on the _primary_ side of the transformer to adjust the voltage energizing the primary coils.

There is no way that you could adjust the voltage or change the 'taps' of a 120/208 wye system to get a 240V three phase system. The reason is that the connections of the transformer coils is entirely different. 120/208 is what is known as a 'wye' connection, providing 3 phases of 120V from phase to neutral, with 208V between phases. 240V is almost always a 'delta' system, with 240V between phases, and possibly 120V between _2_ of the phases and neutral. If you somehow managed to put together a 240V wye system, you would have 139V phase to neutral on your single phase circuits.

With luck, your motor will be designed to operate down to 208V; check the nameplate or contact the manufacturer. If not, then you will either need to replace the motor or use some sort of buck-boost arrangement.

-Jon
 
  #7  
Old 05-19-06, 10:11 AM
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Transformer

Many responders indicate that I want 240volts. I actually want 230volts, 3 phase for the hoist. I think that once the taps are set on the 3 phase pad mounted transformer, all the three phase secndaries must run at the secondary output voltage delivered as a result of the setting of the taps on the primary side to engergize the coils as desired.

Regarding the squirrel: My office was on and most if not all of the rest of the building was off. I visited with the electrician on the utility pole fixing the problem. They never entered the electrical Room to work on the Main Distribution Panel. That means the squirrel blew two of the cutouts on the pole since I have a wye secondary running at 120/208 volts, 3 phase. One cut-out and respective phase must have survived and this is the one that powers my office. There is no delta here, so the previoius responder was not on track thinking it was a situation involving a delta.
 
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Old 05-19-06, 10:50 AM
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ok let get few thing straghten out here for a sec :,,

most commercal 3 phase power system are genrally are 120/208 wye system [ most common ] and other wye voltage is 277/480 [ i will leave this out for now ]

The other system is Delta it come in either 3 or 4 wire verison but this can get tricky here if 4 wire you have one leg called " wild leg " [ can be ******* or whatever you want to called this ]
the wild leg is genrally 208 volt between line and netrual

right now i am not going to get into this delta system for now it kinda right out of the DIY scope in this forum

anyway let get back to the track for a min for hoist motor most hoist motors will work on 208 wye system with out any issuse related but best bet is get the name plate of the hoist motor and read " VOLTAGE " or " VOLT " it will tell you what voltage it can run safe range it will printed like this " 208-230 " that mean it will work either system but if printed "230 " only you may have to concat the manufacter for spec if can able to run on 208 volt because some hoist motors do have contractor [ switches ] are very senstive with voltage set up .

if the manufacter required " buck and boost " transformer this part is best left to be done by electricican because the connection is pretty compatied.

belive me this matter can be resloved by a electrician check out this device instead try to destory a perfect good hoist motor [ they are not cheap btw ]

if other question please do post it here we will try to help you much as we can withen the guideline in this forum

Merci, Marc
 
  #9  
Old 05-19-06, 11:45 AM
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240V is a 'nominal' voltage, describing a particular type of standard power system. A nominal 230V motor is designed to be connected to this system.

120/208V describes an entirely different type of power system.

-Jon
 
  #10  
Old 05-19-06, 11:55 AM
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Winne: yes i was well aware with the voltage set up

i done alot of motor work as well,

normally majorty of 3 phase motor useally hook up on either 240 or 480 system.

but for single phase yeah they have 120 or 240 volt verison as well.

let get back to the oringal question of this person asking about hoist motor as you did explain it in nice way as i did as well so just be fair for us.

i am not going to slam on anyone face today so why not just shake the hand for now and let it be gone for now ??

thanks
 
  #11  
Old 05-19-06, 02:14 PM
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, all the three phase secndaries must run at the secondary output voltage delivered as a result of the setting of the taps on the primary side to engergize the coils as desired.
Yes
One cut-out and respective phase must have survived and this is the one that powers my office.
As posted prior, it's a possibility but it is very unusual if this is the case.

OK here is a link to a website. In the literature on page 2 there is a table. In it you will find that a motor rated at 230 v which is designed to be used on a nominal 240 v system has an acceptable voltage range of 207-253 volts (See my prev. post as to why)

If you check your power system to find the actual voltage available, you should find that you have adequate voltage. Although not optimum but acceptable.

http://pge.com/docs/pdfs/biz/power_q..._tolerance.pdf

So if you want to change things you can but NEMA lists 207 volts as the minimum acceptable voltage for a 230 v rated motor.
 
  #12  
Old 05-19-06, 05:41 PM
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Originally Posted by french277V
i am not going to slam on anyone's face today, so why not just shake hands and let it be gone for now??
Jon was not addressing your response at all. He was addressing #7 about 230V. Had he not done this, I would have. It has nothing to do with your answer.
 
  #13  
Old 05-19-06, 07:24 PM
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Boline : no problem at all i can understand it

Winne: that ok we are cool today


for oringal poster if need more help or question just be free to ask us we will be more than gald to help you with this matter

thanks you for your time to read this


Merci, Marc
 
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