3 phase high leg problem

[ptonsparky]

Other way around isn't it?

If problem follows the wire the problem is with the source.
If it stays the same problem is with the motor.

That sounds assuring.

 

[cpinetree]

Been crazy here this week, I'll get more info, current draws etc Monday.

This problem area does share FPL transformers with the service that feeds multiple 120/240 3ph motors in a pump area.

Everything seems fine / normal in that area (I'm told), just the shop / office panel has the strange voltages.

Thanks for the help.

 

[ptonsparky]

Other way around isn't it?

If problem follows the wire the problem is with the source.
If it stays the same problem is with the motor.

Taken from Franklins AIM for their pump motors.

"...4. Current unbalance should not exceed 5% at service
factor load or 10% at rated input load. If the unbalance
cannot be corrected by rolling leads, the source of
the unbalance must be located and corrected. If,
on the three possible hookups, the leg farthest from
the average stays on the same power lead, most
of the unbalance is coming from the power source.
However, if the reading farthest from average moves
with the same motor lead, the primary source of
unbalance is on the “motor side” of the starter. In this
instance, consider a damaged cable, leaking splice,
poor connection, or faulty motor winding."

 

[gar]

180817-2103 EDT

cpinetree:

In post #10 I indicated that the voltage measurements you made do not logically correlate with a system that has 120 degrees offset from phase to phase. We at least need new voltage measurements line to line with no load.

Unloaded ordinary transformers do not produce much phase shift from their input, and their output voltage is closely related to turns ratio.

If a remeasurement of the voltages is about the same as the orignal values, then try to find a scope with capability to measure the phase angle between AB and AC. Note there is a scope grounding problem to make this measurement.

.

 

[electrofelon]

The 5% limit only applies to a single three phase transformer that supplies the wild leg system. I have never seen such a transformer, but know they exist.
The utility will use two or three transformers for this type of service with a larger one supplying the 120/240 volt single phase loads. Around here that type of service is typically used where the 3 phase load is very small as compared to the single phase load. Most often they will install this as an open delta. The local utility calls the two transformers the "lighter" and the "kicker", with the lighter supplying the single phase loads and the kicker adding the third phase for the 3 phase loads. Of course that doesn't mean that the single phase loads have not been expanded to the point where they caused the voltage imbalance, but I would expect two legs with a lower voltage if that was the case.

Seattle city light calls them "lighter" and "teaser"

http://www.seattle.gov/light/engstd/docs2/0125.02.pdf

Also SCL usually connects these to two phases and the neutral which I think is technically called open wye not open delta?

 

[gar]

180817-2341 EDT

I have now drawn out the delta voltage vectors from post #1 using a CAD program. High resolution. We are assuming sine waves to make this analysis.

The phase angle between AB and AC is offset from 120 degrees by 3.4 degrees. 123.4 instead of 120.

The vertical distance from AB to C perpendicular to AB is 202.1 .The horizontal distance along A toward B to the perpendicular point is 133.2, whereas neutral is at 243/2 = 121.5 .

The length of CN is 202.4 .

Were these voltage measurements from totally unloaded transformers?

.

 

[kwired]

Seattle city light calls them "lighter" and "teaser"

http://www.seattle.gov/light/engstd/docs2/0125.02.pdf

Also SCL usually connects these to two phases and the neutral which I think is technically called open wye not open delta?

We (non utility people) usually aren't that concerned with the primary side, the secondary side is "open delta" either way if there is only coils of two sides of the delta present.

 

[gar]

180819-1930 EDT

This morning I mace some voltage measurements at our shop where we have a 240 V open delta. Total kVA possibly 250 or somewhat higher with about 2/3 for the single phase transformer, and 1/3 for the stringer transformer. I can't read the transformer labeling.

I have no way to make simultaneous measurements, but my results were Vab = 241.3, Vac = 241.4, and Vcb = 241.2 . The maximum calculate phase deviation from 120 degrees was 0.041 degrees.

There is one building tenant with at least a third of the building that was open with all lights on, and air conditioning. I have no control of this load.

cpinetree we need a redo of the voltage measurements with no load on the power company transformers.

.

 

[cpinetree]

180819-1930 EDT

This morning I mace some voltage measurements at our shop where we have a 240 V open delta. Total kVA possibly 250 or somewhat higher with about 2/3 for the single phase transformer, and 1/3 for the stringer transformer. I can't read the transformer labeling.

I have no way to make simultaneous measurements, but my results were Vab = 241.3, Vac = 241.4, and Vcb = 241.2 . The maximum calculate phase deviation from 120 degrees was 0.041 degrees.

There is one building tenant with at least a third of the building that was open with all lights on, and air conditioning. I have no control of this load.

cpinetree we need a redo of the voltage measurements with no load on the power company transformers.

.

That may be all but impossible at this facility. I think we will let them know we need them to shut down one afternoon so we can do that, and it will need to happen sooner than later.

Just so I understand correctly, if the voltages remain close to the same as are being read now, this would point to a POCO transformer issue on the stinger transformer?

 

[cpinetree]

Taken from Franklins AIM for their pump motors.

"...4. Current unbalance should not exceed 5% at service
factor load or 10% at rated input load. If the unbalance
cannot be corrected by rolling leads, the source of
the unbalance must be located and corrected. If,
on the three possible hookups, the leg farthest from
the average stays on the same power lead, most
of the unbalance is coming from the power source.
However, if the reading farthest from average moves
with the same motor lead, the primary source of
unbalance is on the “motor side” of the starter. In this
instance, consider a damaged cable, leaking splice,
poor connection, or faulty motor winding."

Thank you.

This should help solve the where is the source of the problem question.

 

[gar]

180820-1126 EDT

cpinetree:

You seem to imply that there is a considerable load on the power company transformers in question, and you can not unload them.

Based upon my measurements on my open delta there is something grossly wrong with your delta source, and it would seem to be a power company problem.

I am assuming you have just two transformers.

What exists between the transformers and the panel where you are making measurements other than simple wires?

If these transformers supply other panels, then what are the voltages at the other panels?

If you change loading by a large amount on the panel, then how do the voltages change?

When you have two voltages close to being equal and near nominal, and one very far off, then there is something wrong in phase angle in a 3 phase system. Then the question is how can this happen? Transformer leakage inductance and a large load can produce phase shift, but you also get voltage drop. Since nominal voltages existed for 2 phases, and not for the 3rd it is unlikely that load was the cause.

It will be interesting to learn where problem is.

.

 

[gar]

180820-2441 EDT

jaggedben:

In an e-mail I received you ask:

Here is the message that has just been posted:***************

---Quote (Originally by gar)---
180816-1729 EDT

Something is very wrong.

The sum of the voltages around a delta has to equal zero. ...
---End Quote---
Still true if it's an open delta?
***************

Open delta has nothing to do with it. The answer is yes.

View it this way --- Adding Vab + Vbc has to equal Vca. Self evident obvious.

Rearrange the equation and you have --- Vab + Vbc - Vca = 0

.
.