Phasing a tie breaker question

[rgepsii]

When phasing a tie breaker and you have 0 volts on A phase and 0 volts on B phase and 480 volts on C phase what is the right way to phase this .Do you roll the high side or the low side or both and what phases do you roll .Or do you roll phases on both low side or high side of each transformer

 

[Smart $]

When phasing a tie breaker and you have 0 volts on A phase and 0 volts on B phase and 480 volts on C phase what is the right way to phase this .Do you roll the high side or the low side or both and what phases do you roll .Or do you roll phases on both low side or high side of each transformer

When you say 0 volts on A phase, what is your reference. That is, voltage measurements require two points of contact. With A phase being one, what is the other?

Also note that with two sources, you will have to distinguish each phase (technically its a line, not a phase). For example, A1 and A2.

 

[rgepsii]

Phasing a tie breaker

Phasing a tie breaker

from what i understand if are checking the phasing of a tie breaker, you are making sure that the line and load side of the breaker are in phase meaning they are on the same rotation. what i dont understand from this question is that is it posible that only leg are out of phase and the other two are in phase?

 

[GoldDigger]

from what i understand if are checking the phasing of a tie breaker, you are making sure that the line and load side of the breaker are in phase meaning they are on the same rotation. what i dont understand from this question is that is it posible that only leg are out of phase and the other two are in phase?

So this is a hypothetical test or homework question rather than a real life experience?
I agree with you that the only way to get the voltage readings you mention is if one or the other side is not a correct three phase delta or wye regardless of any possible phase rotation.
Example: If one side has the A line at zero degrees, the B line at 120 degrees and the C line at 60 degrees instead of 240 degrees (that is, polarity reversed) then you could get this kind of situation.

 

[Smart $]

from what i understand if are checking the phasing of a tie breaker, you are making sure that the line and load side of the breaker are in phase meaning they are on the same rotation. what i dont understand from this question is that is it posible that only leg are out of phase and the other two are in phase?

No, it is not possible if the transformers are configured the same. If one has reversed rotation, you'd get voltage across two of the pairings. If configured the same except rotation was rolled, you'd get voltage across all pairings.

 

[big john]

...Example: If one side has the A line at zero degrees, the B line at 120 degrees and the C line at 60 degrees instead of 240 degrees (that is, polarity reversed) then you could get this kind of situation.

Agreed, but if his sequence was out then he would have voltage proportional to the phase shift. I've done a lot of paralleling and have never seen or heard of two good and one bad phase. I suspect measurement error.

What are the odds that these two systems are both ungrounded deltas?

 

[Smart $]

So this is a hypothetical test or homework question rather than a real life experience?
I agree with you that the only way to get the voltage readings you mention is if one or the other side is not a correct three phase delta or wye regardless of any possible phase rotation.
Example: If one side has the A line at zero degrees, the B line at 120 degrees and the C line at 60 degrees instead of 240 degrees (that is, polarity reversed) then you could get this kind of situation.

I'd be have to think long and hard on how wire a transformer and come up with only one line that's 180? out of phase with its mate on the other transformer. Reversing a transformer's polarity essentially just rolls the phases 180?. About the only way I can think of to possibly do this is to roll or reverse-connect voltage taps...???

 

[JRW 70]

What if both transformers are delta. Then one has a grounded
phase, and the other does not. Would this not give the 480V
indicated above? Transformer specs. could lend clarity to this.

 

[Smart $]

What if both transformers are delta. Then one has a grounded
phase, and the other does not. Would this not give the 480V
indicated above? Transformer specs. could lend clarity to this.

Well one grounded, one not, both to a tie breaker, would be either a violation or bad wiring, right???

I don't see how grounding would make the any difference. Grounding is what would give one measurements at nominal voltages. If one is and one not, I'd expect a measured variance from nominal, but not only one pairing at 480V and the others at 0V. JMO

 

[jim dungar]

When phasing a tie breaker and you have 0 volts on A phase and 0 volts on B phase and 480 volts on C phase what is the right way to phase this .Do you roll the high side or the low side or both and what phases do you roll .Or do you roll phases on both low side or high side of each transformer

You need to provide all of possible voltages and the transformer connections (delta-wye?), but I would look into the probability you have to: Roll primary phases 1 postion, while keeping the same Phase sequence (rotation).

What do you measure:
X1-X1'
X2-X2'
X3-X3'
X1-X2'
X1-X3'
X2-X1'
X2-X3'
X3-X1'
X3-X2'

 

[GoldDigger]

I'd be have to think long and hard on how wire a transformer and come up with only one line that's 180? out of phase with its mate on the other transformer. Reversing a transformer's polarity essentially just rolls the phases 180?. About the only way I can think of to possibly do this is to roll or reverse-connect voltage taps...???

You cannot do it with a delta, or if the three windings were totally independent at both ends you could do it, but it would blow up from circulating currents.
But with a wye output where the center point is not hard wired (as when using three transformers instead of one three phase), you could reverse the polarity of one leg of the wye.
The result would not be a usable three phase system, but if all of the loads are on the other side of the tie or are all line to neutral you might not notice it right away. The neutral current would be awfully high though. My SWAG is about twice the single line current.

 

[iceworm]

Disclaimer: I have only phased a few systems - maybe 10 total, a few 13.8kv and several 480V. It's okay if you tell me I am all wet.

Terminalogy note: A "measurement pair" is A-A, or B-B, or C-C across the open Tie CB.

In every case the two systems had a common reference - either Grounded Y or HRG Y. There are only a few ways they can be connected:
Y - Y connected correctly - all three pairs measure )V
Y - Y can have one side rolled one slot - all three pairs measure 480V
Y - Y can have one side with two phases reversed - One pair = 0V, two pairs = 480V
That is easy to see that the OP case can not be.

There is a possible case where the one of the phases is swapped with the Neutral - Grounded a phase and brought out the neutral as a phase. I made a vector sketch, looks like two pairs at 277V and one pair at 554V - It's wierd looking, don't hold me to it

Now, pictureing two ungrounded, 480D systems, one tied to each side of a Tie CB. Put three meters, one on each pair. There is no common reference. They could read anything.

So, my question to the OP is as already asked: Is this something you have seen? Other than an internally mis-wired transformer, I don't see how this could be.

Slow poster, following GD post 11, If this is something you have seen, I'd be checking each xfm output

ice

 

[Smart $]

You cannot do it with a delta, or if the three windings were totally independent at both ends you could do it, but it would blow up from circulating currents.
But with a wye output where the center point is not hard wired (as when using three transformers instead of one three phase), you could reverse the polarity of one leg of the wye.
The result would not be a usable three phase system, but if all of the loads are on the other side of the tie or are all line to neutral you might not notice it right away. The neutral current would be awfully high though. My SWAG is about twice the single line current.

Hadn't considered a bank of three 1? pots... but all the same, the voltage on wye secondaries wouldn't be 480V across a pairing with one reverse polarity winding. It'd be 554V...

PS: Don't forget changing the primary configuration also changes the secondary if you want to consider other possibilities... such as a wye-delta.

 

[big john]

What if both transformers are delta. Then one has a grounded
phase, and the other does not....

That's good thinking. I was thinking that if they were both ungrounded there's a chance voltages were floating around while OP was taking his measurements, and that might explain it. But your answer seems more likely.

When phasing a delta the first thing you're supposed to do is check for grounds precisely for that reason. It would be nice to know exactly what L-G was on all conductors.

 

[Bugman1400]

I've had to phase many busties. The problem I see most is when the xfmr mfr doesn't build the xfmr according to the nameplate. So, if you look at the nameplate, it may say X0X1X2X3 but, it is actually X0X3X2X1. If the lowside terminals are rigid bus and attached directly to one side of an MCC then, you cannot swap any of the highside cables to adjust for the error. I've always had to adjust the lowside busbar.

 

[Phil Corso]

Gentlemen?

In my experience there are two predominant Phasing-In problems associated with a Tie-Breaker: a) Reversed Phase?Sequence (RPS); and b) Different-Winding Polarity, (DWP)!

The first problem, RPS, can be corrected with the Phase-Rollover technique. The problem occurs when the phase-sequence of, say the left-hand supply to the breaker is A-B-C, while the right-hand supply is C-B-A!
It is usually occurs because of an electrical-design flaw, that is, the bus or feeder-cable between the Xfmr and Switchgear, is drawn as a ?mirrored? arrangement (ABC-CBA) rather than an identical Arrangement (ABC-ABC)! (Remember, in trig it was called ?reflection about the vertical-axis?!)
As an example, consider a Wye, 120 V system. Then the ?measured paired? voltages are: A-A? = 0 Volts; B-B? and C-C? = sqrt(3) x Nominal or 208 Volts!

The second problem, DWP, can?t be solved using the Phase-Rollover technique, because it involves changes to the Xfmr?s internal connections! It usually occurs when one or the other Xfmr is replaced!
The corresponding ?measured pairs? are: A-A?, = 2 x nominal or 240 Volts; B-B? & C-C? = Sqrt(3) x Nominal or 208 Volts!

Regards, Phil Corso

 

[Phil Corso]

Gentlemen,

Correction: DWP "measured pair" voltages => All are 2 x nominal or 240V!

Phil