Phasing a Tie Circuit Breaker

[Larry5443]

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.

[ruel guanzon]

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.

roll the high side and roll phase B and C?.

[ruel guanzon]

roll the high side and roll phase B and C?.

Hi Larry! did I get this one right?

[Larry5441]

Hi Larry! did I get this one right?

No you did not what did you use for a reference ,you guessed lol sorry

[madMAX]

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.


Roll B and C on the load side? I don't think rolling the high side would result in 0 volts on the secondary, it would probably be like 340 or something.

[drrios1]

Hello Larry
I'm confused.
I have never had my readings like you said. I may have one phase is 0 and the other 2 read 480.
But I have never seen 2 correct and 1 incorrect.
Please elaborate or give me some more help.
The only thing I can think of is rotation but I still believe only 1 would be correct and 2 incorrect
Thanks for sharing this is making me think about how much I haven't seen

[jl8200]

You cant have a single roll on a 3 phase system. 2 phases would be reading voltage and one would read zero. This isn't possible because you have to swap two phases if phasing isn't correct. Maybe im not understanding the question...




Hello Larry
I'm confused.
I have never had my readings like you said. I may have one phase is 0 and the other 2 read 480.
But I have never seen 2 correct and 1 incorrect.
Please elaborate or give me some more help.
The only thing I can think of is rotation but I still believe only 1 would be correct and 2 incorrect
Thanks for sharing this is making me think about how much I haven't seen

[joaogemal]

There's no answer for this question, not in the way it is posted.

[SecondGen]

I agree. :confused: Can we get some clarification on this question Larry?



There's no answer for this question, not in the way it is posted.

[joaogemal]

See the picture.

But, if the question was like:
You read 480 Volts on phase A and B, and Zero Volts on phase C then, the solution will be:
Roll A and B on one side of the breaker.

31

[madMAX]

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?


Roll A and B on one side of the breaker.

[joaogemal]

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?

The question didn't give much information although we can assume this is about a switchgear and, a new installation.
What this mean? It is a double-ended Switchgear and probably all the bus work is done, the transformers came in disconnected and were connected to the line side of the main breaker, In this case my best option is doing on the secondary side of the transformer.

As you can see more information is necessary to make a decision and Yes, it can be done on the primary side of the transformer. One of them, of course.

The answer is that, swap two phases, in one of the sides, which means change rotation of one side. In truth, there's a considerable suppositions for this question itself.

One side has phase sequence ABC 32 and the other side ACB

[wild turkey]

What is the correct answer

[stuebes]

The question has an impossible scenario for two three phase 480V sources. The measurments would have to be 0V, 0V, 0V; or 0V, 480V, 480V; or 480V, 480V, 480V.

For proper phasing with a 0V, 480V, 480V scenario, simply change the two 480V phases from only one source.

Anyone doing closed transition phasing the first time should have an experienced set of eyes for guidance. No room for error here.

[Larry5443]

The question has an impossible scenario for two three phase 480V sources. The measurments would have to be 0V, 0V, 0V; or 0V, 480V, 480V; or 480V, 480V, 480V.

For proper phasing with a 0V, 480V, 480V scenario, simply change the two 480V phases from only one source.

Anyone doing closed transition phasing the first time should have an experienced set of eyes for guidance. No room for error here.

The answer is one of the transformers is bad ,second we no what we are doing so watch the negative comments .

[Larry5443]

The answer is one of the transformers is bad ,second we no what we are doing so watch the negative comments .


All phases read 120 volts across each other on a 480 volt system ,the secondary are hard bus on both sides.What is the best solution for this situation .I will let you know how we fixed it later..

[SecondGen]

The answer is one of the transformers is bad ,second we no what we are doing so watch the negative comments .


I am confused because "one of the transformers is bad" was not an option in the original question:


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.

[SecondGen]

Has anyone seen this question on the NETA exam? This question would get me because NETA looks for best answer, and if my two best options came down to roll the primary of one transformer and roll the secondary of one transformer I would have to say roll the primary of one transformer, because the transformer will have to be shut down anyway and it would be much easier to switch two leads inside of a primary switch than who knows how many on the secondary side of the switchgear.

If the option said roll either, that would be different story. So I would be curious to know exactly how this question is worded.




The question didn't give much information although we can assume this is about a switchgear and, a new installation.
What this mean? It is a double-ended Switchgear and probably all the bus work is done, the transformers came in disconnected and were connected to the line side of the main breaker, In this case my best option is doing on the secondary side of the transformer.

As you can see more information is necessary to make a decision and Yes, it can be done on the primary side of the transformer. One of them, of course.

The answer is that, swap two phases, in one of the sides, which means change rotation of one side. In truth, there's a considerable suppositions for this question itself.

One side has phase sequence ABC 32 and the other side ACB

[joaogemal]

The answer for the problem, in a scenario of: 0 Volts, 480 Volts, 480 Volts is.....
- roll the two phases with the 480 Volts reading -
To make a decision where are we going to roll the two phases (?)
Yes, you have lots of options with different scenarios. That is the beauty of making decisions.

[joaogemal]

The answer is one of the transformers is bad ,second we no what we are doing so watch the negative comments .

With due respect I didn't see any negative comment. As a matter of fact and as a good professional, any safety advise should be always welcome. I like to work around people that don't loose any opportunity to remind us about safety.
Keep in mind, that day the accident will happen is not tomorrow, is today if we don't take care of each other. Team work.

And yes, the question wasn't very well formulated, there was no "transformer is bad" in the answers. Unless, of course, the intent was to misled your audience.

[SecondGen]

Keep in mind, that day the accident will happen is not tomorrow, is today if we don't take care of each other.

Well said. Safety should always be #1 priority. Everyone goes home at the end of the day.

[joaogemal]

At the end, that is what we fight for.
Thank you

[Mmfz85]

See the picture.

But, if the question was like:
You read 480 Volts on phase A and B, and Zero Volts on phase C then, the solution will be:
Roll A and B on one side of the breaker.

31

The way you should phase at the tie cubicle is this. With appropriate meter go to A phase on both sources. You should read 0. While keeping one lead on A phase take the other lead to B Then C phase to the other source. While going to B and C phase you should read line - line voltage. The reason you read 0 is because of the phasor direction or vectors. The are both at 0 degrees.

[joaogemal]

The way you should phase at the tie cubicle is this. With appropriate meter go to A phase on both sources. You should read 0. While keeping one lead on A phase take the other lead to B Then C phase to the other source. While going to B and C phase you should read line - line voltage. The reason you read 0 is because of the phasor direction or vectors. The are both at 0 degrees.

Not really. In this situation specific is about rotation. remember that this case is not for paralleling two different sources. They are the same vectors, just coming from different places.

And, just to compliment, not only the appropriated meter, but also, and more important, PPE, live work permit and all NFPA 70E requirements for LIVE Work authorization.

[Mmfz85]

Not really. In this situation specific is about rotation. remember that this case is not for paralleling two different sources. They are the same vectors, just coming from different places.

And, just to compliment, not only the appropriated meter, but also, and more important, PPE, live work permit and all NFPA 70E requirements for LIVE Work authorization.

The angle and magnitude on either source of the same phase should be at the same degree upon the vector. That's why you read 0. Just explains why you read zero. And thanks for the safety tip.

[Mmfz85]

The angle and magnitude on either source of the same phase should be at the same degree upon the vector. That's why you read 0. Just explains why you read zero. And thanks for the safety tip.

Also you are parrelling if the tie closes. That's why you need to make sure both sources are the same vextor

[SecondGen]

Found this really good article from NETA World that covers this topic in depth. Here are some highlights related to this thread:

The only way to verify that two similar voltage systems are in phase is to determine that zero volts (or nearly zero) exists between the same phases of the two systems. A rotation (or phase sequence) meter is insufficient and unnecessary for verifying phasing. A rotation meter is useful only to check that motors will rotate in the correct direction after reconnecting leads or other parts of the power circuit.

A phase-angle meter or an oscilloscope is useful to determine if the voltages of one circuit leads or lags the voltages of another circuit, but they are not necessary. The minimum equipment required for verifying phasing is either a voltmeter or phasing sticks as necessary for the system voltage.

To understand the phasing process, it is necessary to know the voltage and phase-angle relationships that exist between the same phases of two systems (see table 1). It is assumed that the phase-to-phase voltages of the two systems are identical.

44

SITUATION # 2: Transformer or Tie Switch Leads Connected in Wrong Sequence
Phase-to-phase voltage is measured between the same phases of each system. The systems both have the same rotation but are 120º out of phase as indicated by the phase to-phase voltage. To correct, move the leads on one system at the transformer primary, secondary, or at the switch such that what was A is B, what was B is C, and what was C is A. If the systems are still 120º out of phase, repeat the process one more time. The use of a phase-angle meter would indicate which way to shift the leads, but that is not actually necessary.


Full article is attached. It covers some other common phasing scenarios found in the field for those who wish to read further into this subject.

[Mmfz85]

Thank you for this. As it explains what I was expressing in great detail.