Transformer help!!

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chris648

Member
Location
Ohio
I apologize if I posted this under the wrong section. I have a GE 5 KVA 480 or 240 to 120 240 single phase transformer. Model number 9T21B1004G02 . My issue is when energized on 480 I have 240 from phase to phase. 130 from X1 to ground, but only 50 volts X4 to ground. I have tried a 2nd transformer, exact same result. Hooked it to a different power source, same result. All the obvious has been checked. Proper input voltage and that. I have hooked it up bonded and un bonded, ground to water line, ground to ground grid. Nothing is changing. Im still questioning if this transformer can be used to feed a small 120/240 volt panel and get both voltages. According to GE it is. I have been on the phone with GE and we have went over everything step by step. Any help would be appreciated with this model.
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
You say that you grounded the transformer and then took you voltage measurements, what exactly did you ground?
 

Besoeker

Senior Member
Location
UK
I apologize if I posted this under the wrong section. I have a GE 5 KVA 480 or 240 to 120 240 single phase transformer. Model number 9T21B1004G02 . My issue is when energized on 480 I have 240 from phase to phase. 130 from X1 to ground, but only 50 volts X4 to ground. I have tried a 2nd transformer, exact same result. Hooked it to a different power source, same result. All the obvious has been checked. Proper input voltage and that. I have hooked it up bonded and un bonded, ground to water line, ground to ground grid. Nothing is changing. Im still questioning if this transformer can be used to feed a small 120/240 volt panel and get both voltages. According to GE it is. I have been on the phone with GE and we have went over everything step by step. Any help would be appreciated with this model.
I assume it's double wound? i.e. the primary 480V winding isolated from the 120-0-120V secondary?
Is the centre tap of the 120-0-120V connected to ground?
If not, you could measure almost anything from X1 and X4 to ground.
 
T

T.M.Haja Sahib

Guest
I apologize if I posted this under the wrong section. I have a GE 5 KVA 480 or 240 to 120 240 single phase transformer. Model number 9T21B1004G02 . My issue is when energized on 480 I have 240 from phase to phase. 130 from X1 to ground, but only 50 volts X4 to ground. I have tried a 2nd transformer, exact same result. Hooked it to a different power source, same result. All the obvious has been checked. Proper input voltage and that. I have hooked it up bonded and un bonded, ground to water line, ground to ground grid. Nothing is changing. Im still questioning if this transformer can be used to feed a small 120/240 volt panel and get both voltages. According to GE it is. I have been on the phone with GE and we have went over everything step by step. Any help would be appreciated with this model.

Have you checked voltages with another meter?
 

chris648

Member
Location
Ohio
I bonded X2 and X3 to the frame of the transformer with my with my grounds. From there carried my grounded and grounding conductors to the 120/240 panel. When I hooked this to a different 480 power source I checked voltages right at the transformer and had the same readings. All threads i keep reading people has used this transformer in a control application, in a shop or factory. I cant find where anyone has used it to feed a 120/240 volt service. Im thinking its wound to eathier deliver 120 or 240. Not both at the same time. honestly it has me, a electrician for 18 years feeling like a first year APP.
 

chris648

Member
Location
Ohio
The diagram has me confused, it doesnt show a a center tap, it just has a ground on the frame. ...... and yes a different meter has been used.
 
T

T.M.Haja Sahib

Guest
I assume it's double wound? i.e. the primary 480V winding isolated from the 120-0-120V secondary?
Is the centre tap of the 120-0-120V connected to ground?
If not, you could measure almost anything from X1 and X4 to ground.

Please do not confuse line capacitance voltages here.That is applicable for utility transformer connected to distribution lines with their neutral terminal ground connection accidentally broken.
 

Besoeker

Senior Member
Location
UK
Please do not confuse line capacitance voltages here.
What!!!
If no part of the secondary is grounded there is no ground reference for the voltage measurements wrt ground. They are therefore indeterminate.
It's a simple concept. Or ought to be.
 
T

T.M.Haja Sahib

Guest
I bonded X2 and X3 to the frame of the transformer with my with my grounds. From there carried my grounded and grounding conductors to the 120/240 panel. When I hooked this to a different 480 power source I checked voltages right at the transformer and had the same readings. All threads i keep reading people has used this transformer in a control application, in a shop or factory. I cant find where anyone has used it to feed a 120/240 volt service. Im thinking its wound to eathier deliver 120 or 240. Not both at the same time. honestly it has me, a electrician for 18 years feeling like a first year APP.

Feeding a 120/240 volt service may not be an issue;check to see you have not exceeded its KVA capacity marked on its name plate.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
The diagram has me confused, it doesnt show a a center tap, it just has a ground on the frame. ...... and yes a different meter has been used.
The center tap is when you tie (wire nut) X2 and X3 together, this makes one single winding between X1 and X4, you will then Ground (earth) X2 and X3 as a single point.

After you have done this take another set of readings from X1 to X4, X1 to X2-3, X4 to X2-X3.

Roger
 

chris648

Member
Location
Ohio
thats where the problem is, X1 to X4 = 240 volts , X1 to ground = 130 volts, X4 to ground = 50 volts, Ground is good ... two different 480 services, two different transformers but same model number, same voltage readings. Now you see why i feel like a first year cub again ??... :(
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
there hasnt been a load put on it because Im not getting the desired voltages, so the KVA isnt exceeded.
After you have done what I described above go ahead and apply an incandescent lamp load across X1 to X2-3 and at the same time put a load on X4 to X2-3, then take readings again.

Roger
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
thats where the problem is, X1 to X4 = 240 volts , X1 to ground = 130 volts, X4 to ground = 50 volts, Ground is good ... two different 480 services, two different transformers but same model number, same voltage readings. Now you see why i feel like a first year cub again ??... :(
What have you done with X2 and X3?

Your readings will be between X1 to X2-3 and X4 to X2-3 don't read anything to ground.

Roger
 

chris648

Member
Location
Ohio
X2 and X3 are tied together and tied to the frame, grounding and grounded conductors, then taken to the panel, X1 to ground = 120, X4 to ground 50 volts
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
It is not the transformer. It is how you have it connected and the voltage measurements you are making.

The transformer is a dual coil secondary, it has one 120V coil from X1-X2 and one from X3-X4. The coils can be interconnected in 3 different ways.

In parallel for 120V 2W output; L1 to X1, X1 to X3, X2 to X4, and X4-L2; in this case you would connect either X1 or X4 to ground.
In series for 240V 2W output; L1 to X1, X2 to X3, and X4-L2: in this case you could connect either X1 or X4 to ground.

But the connection you want is:
In series and center tapped for 120/240V 3W output; L1 to X1, X2 to X3, and X4-L2: in this case you connect X2 to ground and this becomes your neutral.
 

Besoeker

Senior Member
Location
UK
thats where the problem is, X1 to X4 = 240 volts , X1 to ground = 130 volts, X4 to ground = 50 volts, Ground is good ... two different 480 services, two different transformers but same model number, same voltage readings. Now you see why i feel like a first year cub again ??... :(
If the connections X2 and X3 are tied together AND connected to the same ground that you couldn't/shouldn't get those readings. It would imply that you don't have equal voltages across each of the two secondary windings.

Two suggestions.
Measure each secondary winding. X1-X2 and X3-X4. They should both be the same at 120V.
Measure X2 to ground.
Measure X3 to ground.

OK. That's three.

Post the results here.
 

chris648

Member
Location
Ohio
Guys thanks for all your help, and assuring me i hadnt lost all my electrical knowledge and should be flipping burgers somewhere. ill end this with this point, something you would think i would know by now, unless you yourself make up the connections dont take someone elses word for it. sometimes you just gotta break the rules and slip away and put your hands on it yourself. Now how do I explain this one to the shop???.... thanks again guys, and this web page is going directly to my favorites list for future help or my input to others needing help!!
 
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