Delta to Wye: one phase of the wye is high!

Status
Not open for further replies.
S

Sami Burton

Member
Hello All,

One of my electricians has called me from the field with the following question and neither one of us have a clue:

They are testing the phases to ground on the wye side in the field. Two of the phases are running at 110, but for some reason one phase is running at 130. Is this because the delta is transferring its high leg to one phase of the wye? We do not know why one phase on the wye is higher to ground!?!

Any help would be greatly appreciated.

Thanks!
 
charlie b

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I infer that you are talking about the secondary side of a delta-wye transformer. Is that right? Is it under load? Are the loads balanced (i.e., do you have current readings on the three phases)?
 
brian john

brian john

Senior Member
Location
Leesburg, VA
1. What is the primary voltage phase to phase, phase to ground.
2. What is the secondary voltage phase to phase, phase to XO and phase to ground.
3. As noted is it properly grounded at XO.
4. Check all the taps are set properly and the same.
5. As noted is the system under load if so what are the phase currents?
6. Did they megger the transformer and (I know the answer but will ask anyway) do they have access to a TTR.

Not necessarily in order of importance but as it came to my feeble mind.
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Sami, welocme to the forum! :)

Sami Burton said:
Two of the phases are running at 110, but for some reason one phase is running at 130. Is this because the delta is transferring its high leg to one phase of the wye? We do not know why one phase on the wye is higher to ground!?!
Click to expand...
Presuming nothing weird happening, with a Delta/wye transformer, the only way a secondary line-to-neutral voltage could be different, would be for the line-to-line voltage on one primary to be different.

As with any line-to-line or 3-phase load, the voltage to neutral on any conductor has absolutely no bearing on it. You need to check the line-to-line voltages on the primary. Is the source an open or full Delta?
 
M

mull982

Senior Member
Sami Burton said:
Hello All,

One of my electricians has called me from the field with the following question and neither one of us have a clue:

They are testing the phases to ground on the wye side in the field. Two of the phases are running at 110, but for some reason one phase is running at 130. Is this because the delta is transferring its high leg to one phase of the wye? We do not know why one phase on the wye is higher to ground!?!

Any help would be greatly appreciated.

Thanks!
Click to expand...


Is it possible that the X0 point is ungrounded as others mentioned and the voltages you are reading are capacitive coupled voltages? These can coupled voltages can sometimes lead to strange readings.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
What are all of the actual voltages at the transformer?

Delta Primary
H1-H2
H2-H3
H3-H1

Wye Secondary
X1-X2
X2-X3
X3-X1
X1-N
X2-N
X3-N
N-G
 
S

Sami Burton

Member
Thank you!

Thank you!

Everyone, thank you for your posts! They were very helpful. It is not under load. We are going to bond the XO to the ground.

P.S. What does "megger" mean?
 
Status
Not open for further replies.
Top