Synchronizing (2) feeders that are out of phase with each other 5

[bdn2004]

I work at a plant that is considering putting in a 4160V auto transfer scheme on their cooling water pumps. They want to do this with a main-tie-main-tie-main type configuration ( 3 - 4160V feeders). The problem is that one of the feeders is 60 degrees out of phase with the other two.

Is this possible? Are there more questions I need to ask?

 

[bdn2004]

Here is the basic simplified single line diagram.

 

[dpc]

Do you have the winding information on the three-winding transformer (delta, wye, etc?) I don't see it on the sketch, although it might have been cut off. You will have to get the phasor information from the transformer nameplate or shop drawings.

 

[waross]

I don't see the connection/transformers from the "Two generators that produce the primary voltage at 15kV and its transformed down to 4160V." and the 20V/138kV system. Is that not shown or is my browser clipping off part of the drawing.
The interconnection transformer between the old system and the new system must be considered also.
Thanks

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[burnt2x]

bdn2004,
Hi!
I don't see any problem synchronizing the feeders seeing your single-line diagram!
G3 (additional feeder source)can be adjusted to be in-phase with the existing system (two-4160V feeders) prior to closing!

 

[stevenal]

"..all of the generators would be synchronized to the outside world"

I see no outside world in the one line. Without a common reference, the phase shift between the two systems is indeterminate from the diagram, and would changing in practice. You can sync at the 4.16kV tie as burnt2x said if the one line is complete.

 

[bdn2004]

Attached is some more information that I took from the nameplate of the transformers. There are two sheets. Do I need to get more before trudging through the technical details? Like the wiring diagrams?

Note that the single line sketch is an EXTREMELY abbreviated version of the actual single line of the plant.
This is just the information I thought required to answer my question.

 

[stevenal]

Did your abbreviation remove any of the "outside world" ties to a common power grid or any other connections between the systems other than the proposed 4160V tie? If so, please show them. How do you know the systems are 60 degrees out at the tie?

 

[waross]

If the system is as you have shown it follow the following steps.
1> Install a synchroscope across the tie breaker.
2> Put G1 and G2 governors in droop mode.
3> Manipulate the set points on one or both governors until you come into synchronization.
4> Close the tie breaker.

That is the correct answer based on the supplied information.
If you have not given us complete information then this answer is probably wrong.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

On reread, I see that one of the generators is connected to the grid. Are the other two as well? At what voltage? If the systems connect to the grid at two different voltages, youll need the phase relationship between the two voltages also. Probably want that nameplate diagram from your step up transformer also.

 

[bdn2004]

Just as an update to this question...

A company named Beckwith Electric makes a product they call the "Sychrotran Motor Bus Transfer System". This product eliminates the need for a parallel transfer and keeps the pumps running during the transfer - which is the ultimate goal.

What I didn't understand with the proposed method of re-wiring the transformer is what it did to the rotation of the motors? Changing the leads around seems like it would make the motors spin in the opposite direction.

 

[slavag]

Bdn2004, HBT is another system. I'm not familar with Beckwith relay, but commissioned several same systems.
HBT have 4 options:
1. Fast transfer ( make and break command simultanesly).
2. 1st phase concidience
3. residual voltage Ubus<0.3-0.4Un transfer
4. long time trnasfer.
2,3, and 4 are break before make, in those case you don't need paralleling, right.
But, what you can do with manual transfer: back bus to regular/main supply? Possible again point2 , dangerous.
Regards.
Slava

 

[davidbeach]

Nope, all of the rewirings I described have the same phase rotation as the original. That's why when leads are swapped on the primary it is also necessary to swap leads on the secondary. Inside the transformer the phase rotation is "backwards" but not outside.

 

[waross]

No. If you have the transformer connections set for proper paralleling of the bus, there will be no change in phase rotation. If the connections are incorrect, whether for phase shift or for rotation or both, there will be a traumatic event when the tie breaker is closed. The motor(s) will probably be adding current to the fault. However, if your connection changes result in a phase reversal just swap two leads on the tie breaker.

BUT am I missing something or have I made a mistake downloading your sketches?
You are showing G1, G2, t1, and T2 as an islanded, stand alone system. If so, then the systems may be connected directly.
What you have according to your sketch is not a phase shift, but two systems with one 60 deg. out of phase with the other. The phase difference is easily changeable. If you slightly change the setting of the governor on either G1 or G2 the phase shift will start to drift. When it drifts to the zero position, close the tie breaker. The only extra equipment needed is an inexpensive synchroscope. You may want to add a sync check relay.
If this is not the case, then please post a complete drawing.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

http://www.beckwithelectric.com/bse/mbt-products.htm

The product described does attempt a parallel transfer, but will also do a high speed transfer. All of this is unneeded if there is a fixed phase angle difference that can be corrected by swapping leads, but might be a solution if systems are independent.

Very frustrating thread, as bnd2004 ignores our requests for information.

 

[bdn2004]

I didn't mean to have the most frustrating thread...but obviously I'm not grasping this.

If I'm still lacking any info...I made this Visio drawing that should be fairly easy to update.

 

[waross]

Hi bdn2004.
Here's a posting tip.
Click on "Preview Post" instead of "Submit Post" Then you can click on your downloads to see how they will come up. I am only getting the left side of your drawing. I am on a flaky i-net connection so it may be a local problem.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sibeen]

bdn2004, I have the same problem as waross. You need to adjust your drawing.

 

[bdn2004]

The drawing was created on an 11 x 17 border...when I printed it to pdf I bet I didn't set that. It thinks it's 8.5 x 11.

I'll fix it tomorrow and post it again.

Sorry, thanks for the info.

 

[slavag]

Please add vector group,%impedance, power (MVA) of trafos
in your drw.
Regards.
Slava

 

[waross]

hi Slava. Give the fellow a break. We can ask specific questions later. Let's let him post the drawing he has before asking for information that nay be difficult for him to provide. One step at a time.

Bill
--------------------
"Why not the best?"
Jimmy Carter