Dy1 shift - proved +30 ABC & -30 ACB but rotation is confusing

[Manindemand]

At two different stations, I took phase angles from A phase PT on 115kv bus to A B & C metering PTs on 13.8kv bus. I used a Dranetz Phasemeter - model 314. Both transformers are Dy1 and grid is A-B-C CCW.

The station with A-B-C sequence read:
HV A leads LV A by 32 deg
HV A leads LV B by 152 deg
HV A leads LV C by 272 deg

The station with A-C-B sequence read:
HV A leads LV A by 333 deg
HV A leads LV B by 93 deg
HV A leads LV C by 215 deg

When you draw two circles and plot the phases they both indicate A-B-C with CCW phasor rotation.

At the A-C-B station, I expected B and C angles to be the opposite in order to show A-C-B sequence.

Do these readings look correct? Please explain. Thanks

 

[rbulsara]

One of the secondary phases (b and c) are interchanged to get correct rotation and phasing.

 

[Manindemand]

Do you mean - when I thought I was connected to C phase I was really connected to B?

Or do you mean the readings are correct and it's a normal effect?

 

[rbulsara]

I meant it appears that B is connected to C (and C to B)(most likely the physical wire on secondary side, I dont think internal connections or the reading s are wrong.)

Check the rotation for each secondary(or check using a motor with same color wires conected to the same terminals. If the rotation remains the same, then B and C wires are interchanged in one of the secondaries.

 

[rbulsara]

Sorry, I forgot the medium voltagem second time around, i was thnking low voltage secondary (can't use motor))

But therory remains the same. Also hot phasing (direct checking phases) is a more postive test, then relying on the PT connections. You need to make sure that PT wirnig is not messed up in first place.

 

[Manindemand]

I've been searching the forum and was almost convinced that my connections/phases and readings are correct and I just need to view the A-C-B phase rotation in the CW direction (while plotting the degrees in the CCW direction on both circles).

This is one of the threads (by redtrumpet). See his second post in that thread.

thread238-19684 "Now you come to a delta-Y transformer. H1-H2-H3 are connected C-B-A. Is the secondary side phasor: - still rotating a-b-c ccw to match the reference, or a-b-c cw to reflect the fact the transformer phasing was reversed on the primary?"

We just replaced the meter PTs so I know the colors comming from each PT. I will verify the colors did not get rolled on the various terminal blocks upstream from where I took readings.

I'm also wondering if the odd readings are due to the old style Dranetz Phasemeter.

Thanks

 

[busbar]

Depending on what you want to do with the two systems, either be well aware of the difference, or use a [stick-mounted] phasing voltmeter set to check against your PT connections. Clearly in their present configuration the transformers are not parallelable—if that is your goal.

 

[Manindemand]

busbar, no, not trying to parallel them. At the station with A-C-B sequence I needed to take phase angle readings before and after installing new metering PTs on the 13.8kv bus. They are now installed and the before and after readings were the same.

After analyzing the A-C-B readings I was curious how A-B-C sequence readings would compare. I had to drive an hour to a station with highside PTs and A-B-C sequence into the transformer. Using the same phase on the 115kv grid (A Ph), I took readings on A, B and C on the 13.8kv bus. Both sets of readings were taken across Dy1 xfmrs.

When you plot these two sets of angles it's obvious that both A phases are correct (one +30 and one -30). It's also obvious that the A-B-C set plots correctly. But on the A-C-B set, I expected C to follow A when rotating CCW.

 

[rbulsara]

When you say both grids are A_B_C CCW, which grids? 13.8kV? or 115 kV? I presume it is 115 kV.


If the marks are say A,B,C on primary and a,b,c on the seconadary, by connecting A-C-B sequence on the primary, actual seconday 'b' will be on terminal maked 'c' (and actual 'c' would be on terminal marked 'b').

If you took the middle terminal of the secondary of ACB connected transfomer as 'b' then you will get the results you got. I think...

 

[busbar]

manin — A hour apart, eh? That’s a pretty long extension lead for a phasing voltmeter…my misunderstanding.

 

[jbartos]

Suggestion to Manindemand (Electrical) Oct 31, 2003 marked ///\\At two different stations, I took phase angles from A phase PT on 115kv bus to A B & C metering PTs on 13.8kv bus. I used a Dranetz Phasemeter - model 314. Both transformers are Dy1 and grid is A-B-C CCW.

The station with A-B-C sequence read:
HV A leads LV A by 32 deg
HV A leads LV B by 152 deg
HV A leads LV C by 272 deg

The station with A-C-B sequence read:
HV A leads LV A by 333 deg
HV A leads LV B by 93 deg
HV A leads LV C by 215 deg

When you draw two circles and plot the phases they both indicate A-B-C with CCW phasor rotation.

At the A-C-B station, I expected B and C angles to be the opposite in order to show A-C-B sequence.

Do these readings look correct?
///Where did you find the station A-C-B indication? Where did you find the station A-B-C indication?\\ Please explain.
///The measured values indicate that the stations have the same sequence.\\ Thanks

 

[Manindemand]

jbartos, all of our stations have one-line drawings showing the bus configuration, breakers, switches and transformers. The one-line indicates which phase hits each transformer HV bushing.

If both stations had the same sequence then wouldn't both A phases be the same?

Today I went to the A-C-B station (15 min from home) and verified that the original readings are correct.

First I used a cable toner to tone out the cable from LV PT j-box to the metering cabinet in the control building. The wiring from the cable was NOT rolled. I then ran a 100 ft lead from the control building (HV A Ph fuse) out to the LV PT j-box. I set up my phase meter and took readings again. The readings were the same. This proved the cable was not spliced wrong in the ground somewhere.

The next thing I'll do is take our Arbiter Power System Monitor (Model 931A) back to the A-C-B station and compare phase angles. Maybe it's the way the old Dranetz reads.

Is it possible that the readings are correct even with one xfmr A-C-B and the other A-B-C. Both circles plot A-B-C sequence in CCW direction. How could that ever change unless you actually rolled phases in the generator? Phase sequence only changes the rotation of motors and the phase shift through transformers right?

 

[Manindemand]

rbulsara - the grid I'm speaking of is the 115kv grid. The same grid that's interconnected throughout the USA (at higher kv). My understanding is that all generation in the USA (that's not islanded) is A-B-C CCW. It only changes sequence through transformers.

At the A-C-B station:

H1 & X1 are A ph, H2 & X2 are C ph, H3 & X3 are B ph.

When I say I read B phase I mean I read from the PT on the X3 phase.

 

[jghrist]

The phase rotation in some parts of the US is reversed. I know that Georgia Power and Duke Power use reversed phase rotation. I think the original reason for doing so was to confuse Georgia Tech power engineering students.

When you think about it, it is basically a matter of nomenclature. One phase voltage will reach a peak 120° (or 5.55 ms for 60 Hz supply) after another. At Duke Power, they use X-Y-Z CW rotation, which is the same as Z-Y-X CCW. This means that øY will reach a peak 5.55 ms after øZ and øX will reach a peak 5.55 ms after øY. If someone would take a paintbrush and mark all of the Z's with the letter A and all of the Y's with the letter B, and all of the X's with the letter C, then Duke Power would have a system with A-B-C CCW.

When you connect the phases to a Delta-Wye transformer, the rotation matters because it changes the phase relationship between primary and secondary. For a US standard transformer (Dy1), If you connect one phase to H1 and the phase (whatever you call it) that peaks 5.55 ms after that to terminal H2, and the last phase to terminal H3, then the phase connected to X1 will lag the phase connected to H1 by 5.55 ms, or 30°. If you were instead to connect the phase to H2 that peaks 5.55 ms before the one you connected to H1, then X1 would lead H1 by 5.55 ms or 30°.

What you have described is a system with A-B-C phase rotation, with B peaking 5.55 ms after phase A. You have connected A to H1, B to H2, and C to H3 at the station that you call A-B-C sequence and have connected A to H1, C to H2, and B to H3 at the station that you call A-C-B sequence. This is somewhat of a misnomer. The phase sequence is A-B-C CCW for the system, but one transformer has H1-H2-H3 CCW phase sequence and the other has H1-H3-H2 CCW phase sequence.

 

[jghrist]

Correction to my above post. "...the phase connected to X1 will lag the phase connected to H1 by 5.55 ms, or 30°." should read "...the phase connected to X1 will lag the phase connected to H1 by 1.39 ms, or 30°." Similar correction for the next sentence.

 

[mvcjr]

If the 115-kV side of one station is interconnected to the 115-kV side of the other station how could it be that the second station has an ACB phase sequence while the first station has an ABC phase sequence? Both stations should have the same phase sequence.

From the measurements you have given, it seems one transformer is Dy1 (A leads a by 30 degrees) and the other transformer is Dy11 (A leads a by 330 degrees).

God bless!

 

[Manindemand]

Thank you gentlemen for responding. I'm beginning to under stand. It's mainly a nomenclature and terminology issue.

jghrist, when you say Georgia and Duke Power use reversed phase rotation, do you mean they connect their transformers A-H1 C-H2 B-H3 (A-C-B) but their generators run A-B-C (A leads B by 120 and A leads C by 240)? I would think this has to be the case unless Georgia and Duke are islanded.

Your description about H1-H3-H2 CCW - can that also be stated H1-H2-H3 CW ?

mvcjr, the system phase sequence is A-B-C but... one transformer is connected A-H1 B-H2 C-H3 (A-B-C) and the other transformer is A-H1 C-H2 B-H3 (A-C-B). Yes, both are Dy1 transformers.

So as long as SYSTEM PHASE SEQUENCE is A-B-C then my readings are what you would expect?

Thanks again.

 

[jghrist]

I'm not sure about Georgia Power, but Duke Power normally connects their transformers X-H1, Z-H2, Y-H3. The CCW phase sequence of the high side bushings is H1-H2-H3 because the system phase sequence is X-Z-Y CCW. This makes X1 lag H1 by 30° with a Dy1 transformer.

You can have one utility interconnected with another and have different A-B-C phase rotation if one utility names the phases differently. Let's say the phase conductors are physically colored Red, Yellow, and Blue and they are connected to a generator such that the Yellow phase voltage peaks 5.55 ms or 120° after the Red phase, and the Blue phase voltage peaks 5.55 ms after the Yellow phase. If Utility A calls the Red colored wire Phase A, the Yellow colored wire Phase B, and the Blue colored wire Phase C, then their phase sequence would be A-B-C CCW. If Utility B calls the Red colored wire Phase A, the Yellow colored wire Phase C, and the Blue colored wire Phase B, then their phase sequence would be A-C-B CCW.

Yes, you can state that H1-H3-H2 CCW is the same as H1-H2-H3 CW. This may make things harder to understand, however.

 

[mvcjr]

Manindemand,
I would say your readings are correct!

Since you reversed the phase connections to the transformer in the other station it is now functioning like it is a Dy11 transformer although by nameplate it is Dy1.

God bless!

 

[Manindemand]

A little follow up - I took the Arbiter power meter back to the A-C-B station. If you program it's polarity to (+) you read the same angles the Dranetz reads at the A-C-B station. If you program it's polarity to (-) you read the same angles the Dranetz reads at the A-B-C station.

After thinking about this and discussing it here it makes sence now. I guess all the illustrations of A-C-B phasors showing C following A by 120 deg in CCW direction had me confused. I'd rather see those illustrations with CW arrows.

Anyway, while researching this I found this link. I did a google search for ("rotation" phase). Out of 87 pages of results this was the only publication describing the 30 lead and lag effect of delta-wye xfmrs -

http://pm.geindustrial.com/faq/Documents/T60/GET-8431A.pdf

Thank you everyone.