journeyman0217
Senior Member
- Location
- Tennessee
- Occupation
- Electrician
It is tapped to #4 468v...getting 472v on the meter
480v high leg motor issue
- Thread starter journeyman0217
- Start date
ptonsparky
Tom
- Occupation
- EC - retired
They could be about anything from 0 to 480.
ptonsparky
Tom
- Occupation
- EC - retired
Close enough. Are all three phase to phase the same?
My issue with the back feeding of a transformer would be with a delta wye, not yours.
journeyman0217
Senior Member
- Location
- Tennessee
- Occupation
- Electrician
yes getting 472 on all three phases
ptonsparky
Tom
- Occupation
- EC - retired
What are the primary voltages? L-L and L-G
Primary Amperages? Each line.
Is the motor the only load on that transformer?
Primary Amperages? Each line.
Is the motor the only load on that transformer?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
When troubleshooting it is best to make, and provide, all of the possible voltage measurements.
L1-L2
L2-L3
L3-L1
L1-N
L2-N
L3-N
L1-G
L2-G
L3-G
N-G
MD Automation
Senior Member
- Location
- Maryland
- Occupation
- Engineer
As Kwired mentioned above... it's a phasing symbol, which shows the phase shift (if any) between the primary and secondary windings.
In a typical delta to wye it shows the 30 degree shift inherent in that type of transformer.
In your delta to delta, it indicates there is no phase shift.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Notice the label only says HV and LV. If reference feed was prohibited it would use terms like primary and secondary. Sorgel always had application notes on backfeeding their transformers.
My guess is the transformer is almost 50 years old.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Yep.
These same phasing dashes are used with delta-wye connections, although they are commonly misinterpreted to be 'grounding' provisions.
ptonsparky
Tom
- Occupation
- EC - retired
Figured that out, eventually.
I couldn't find it online for a a spec sheet.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Nope. The voltage to ground relation of the primary does nothing to the secondary. Since you have a secondary that doesn't have a center point tap, your choices are to corner ground the secondary or leave it ungrounded.
journeyman0217
Senior Member
- Location
- Tennessee
- Occupation
- Electrician
journeyman0217
Senior Member
- Location
- Tennessee
- Occupation
- Electrician
Nobody could ever tell me what they were, thank you
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Just to clarify on the step-up/step-down thing: this transformer was pretty clearly originally designed as a 'step-down' transformer. As others have noted, this transformer is capable of being used as a 'step-up' transformer, and may even have proper documents for such 'reverse' use.
The clue is the location of the voltage adjustment taps. The voltage adjustment taps change the 'turns ratio' between primary and secondary, so that you can get the correct secondary voltage even if the primary voltage is a bit out of spec.
In the vast majority of cases the voltage adjustment taps are placed on the primary side of the transformer. This lets the voltage adjustment change both the turns ratio of the transformer and adjust the magnetic flux level in the transformer core. If you place the voltage adjustment taps on the secondary side, then if your primary voltage is higher than nominal the transformer core will have excessive saturation and losses.
I have a drive isolation transformer with voltage taps on the secondary side, but this is very rare.
So when you look at that transformer dataplate, and you see the taps on the HV side, you can be quite certain that you have a 480V:240V step down transformer used in reverse.
-Jonathan
journeyman0217
Senior Member
- Location
- Tennessee
- Occupation
- Electrician
So is there such thing as a 480v delta high leg? If so, what would be your voltages?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The NEC had no real prohibition against reverse feeding a transformer until fairly recently, certainly not back when this transformer was made.
journeyman0217
Senior Member
- Location
- Tennessee
- Occupation
- Electrician
Interesting, makes sense.
ptonsparky
Tom
- Occupation
- EC - retired
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Although they rarely, for most of the US, they evidently fo exist.
The high leg would be 415V.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Not every transformer should be run backwards. As previously mentioned taps are an issue. Some small transformers, like machine tool units less than 3kVA may actually have compensating windings on their primary to account for losses in thier cheaper core construction. Finally there is the probability the increased inrush/energizing current may require primary side OCPD which exceeds the NEC limits.
[Soapbox]
The reality is the NEC has their restriction, for manufacturer approval, because too many installers do not follow manufacturers instructions, especially when they are not included with the equipment. This is similar to how SCCR requirements have been added to article 240, in addition to the historical ones in 110.9 and 110.10, or the specific prohibition of 2 grounded conductors I a termination that accepts 2 grounding conductors.[/soapbox]