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

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

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

(OP)
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?

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

2
A live transfer is not possible.  You will need to briefly de-energize the system, allow the motors to coast down, then re-energize from the alternate source.

You should key interlock the main and tie breakers to makes sure someone does not get too creative.  

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

When using delta to wye transformers you will always see a phase shift. The phase shift can be + or - depending on the phase rotation entering the transformer primary.

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

I just noticed you mentioned an auto transfer scheme, so forget the key interlocks.  You will want a time delay or an voltage relay to make sure the bus is dead before the transfer is completed.

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

2
If the phase shift is truly 60° and not 30°, you can do some rewiring of the transformer that is 60° out to line it up with the other two transformers.

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

David may be correct, assuming that this would not screw up the phasing on some other portion of the system.

The 60 deg phase shift does seem odd.  30 degrees would be much more common.  

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

60° is generally a miswired transformer, 30° is a delta-wye transformer.  60° could also be two delta-wye transformers in series.

Rewiring a delta-wye to change the phase shift by 60° will require swapping two leads on the primary and two leads on the secondary.  Assuming an ANSI standard transformer, swapping A&B and a&b will put the low side 30° ahead of the high side instead of 30° behind the high side.  Swapping one pair on the high side and a different pair on the low side will then also add or subtract 120°.

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

Could be two delta-wye units with opposing phase shifts, I guess.   

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

Yeah, that too.

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

Hi.
What do you mean auto transfer scheme?
I see this term several times and would like connect it to my understanding.
For me is: loss of one of infeed, trip of "bad" infeed ( in case of alternative supply), connect of supply.
 Always break before make. I'm correct?
Regards.
Slava.
In case of bus with asinch. motors: Do you use system like to HBT motor bus?

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

That's a good question, in that there are several schemes that can be called auto transfer schemes.
I know of the make-before-break used for source switching.
I know of the break-before-make used more as a auto-transfer for a loss of a source, or for source switching.
There is a scheme called fast transfer, where it is a break-before-make scheme, but with much shorter delays.

It is also possible to run the buses togather, or split, or with parallel sources.

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

Thanks Cranky108. Now it's more clear for me
For make before break scheme we use two terms:
1. Silent transfer.
2. Manual transfer.
Regards.
Slava

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

(OP)
This is a power plant.  Two of the sources come off of generators that produce the primary voltage at 15kV and its transformed down to 4160V. We have another, newer generating system that produces power at 20kV, bumps it to 138kV, then it's transformed down to 4160V. That is the third source that is out of synch with the other two. At present they use the two that are in phase to do make before break transfers. The trick is to bring in the other feeder....There are some good answers here..but I'm still a little confused as how to do this.

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

Normally for this application at a power plant, one of the transformers is made with the 30 degree phase shift in the opposite direction.  This is a common setup.  But without looking at a one-line, I'm not sure this is exactly your situation.

If you already have the transformers, you may be able to reconnect them, as David Beach mentioned.  

You might have a look at this:  FAQ238-1154: Can I parallel a DY1 and DY11 transformer?

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

2*n*30° shifts are available from delta-delta or wye-wye transformers.  (2*n+1)*30° shifts are available from delta-wye or wye-delta transformers.  In both cases n=0,1,...,5.

Within those two groups, you can get 120° changes simply by rolling the connections on either the primary or the secondary (but not both).  To get the 60° shift that sets up the rest of the possibilities you need to swap two phases on the primary and two phases on the secondary.  How the swaps on the primary and secondary relate to each other determines the total phase shift.

Time to start drawing vector diagrams.  Work with the standard delta-wye transformer and work with it until you understand why you get the 30° shift.  Then start changing leads and see what happens to the vector diagrams.

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

It could be a mix of additive and subtractive polarity transformers. That gives a 180 degree shift that looks very much like a 60 degree shift.
But if this is from an independent generator why can't you use the governor control to synchronize?

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

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

Bill, all of the generators would be synchronized to the outside world.  My guess is that the two older generators are connected to the 4160V bus from the terminals of the generator with wye-wye or delta-delta transformers while the output of the newer generator goes through two delta-wye (or a delta-wye and a wye-delta transformer and one of the phase shifts is backwards.  A one-line would be a great help.

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

(OP)
I think the light just went off in my head to what you are telling me...by simply changing the hookups on the primary and secondary we can create the 60 degree phase shift on the secondary. That would be an easy fix at the two existing transformers and it would not hurt anything because they are captive to the load. That would bring them in phase with the alternate feeder.

Frankly that is a great solution and potentially could save us lots of bucks. Thanks!!

The alternate source generator is 300 MW and like DB states is hooked up to the outside world. I'm talking about one of its feeds that is about 10 MW of load. And even it comes off of a large 4160V transformer.

I will sketch up a single line and try to post it tomorrow. I've not done that before.

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

Thank you David. I understand now and agree with you.
Yours

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

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

bdn2004,

On the transformer nameplates, there should be a phasor diagram that will show the phase relationship between the two windings.  You need to copy down all of this information, then  sit down and draw out the phasor diagrams for the entire system you are dealing with.  Then you can determine if reconnecting of the transformers can provide a solution.  It's possible, but it will depend on the transformer connections.  

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

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.

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

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

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

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!

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

"..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.

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

(OP)
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.

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

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?

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

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

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

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.

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

(OP)
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.

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

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

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

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.

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

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

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

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.

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

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

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

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

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

(OP)
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.

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

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

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

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

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

No Problem Bill.
I agreed.
Regards.
Slava

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

Hi. I think Dave(DPC) posted right reason:
"Normally for this application at a power plant, one of the transformers is made with the 30 degree phase shift in the opposite direction.  This is a common setup.  But without looking at a one-line, I'm not sure this is exactly your situation.

If you already have the transformers, you may be able to reconnect them, as David Beach mentioned.  

You might have a look at this:  FAQ238-1154: Can I parallel a DY1 and DY11 transformer?: Can I parallel a DY1 and DY11 transformer?"
It's also common mistake in power plants.

Other issue, for this size of power plant , Becwith relay HBT is good solution.

Regards.
Slava

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

So from the 138kV system to the tie on the left, there is a wye-delta feeding a delta-wye; each providing a 30 degree shift. The overall shift from the 138 system is likely to be 60 degrees, but could be zero if non-ANSI windings or unconventional connections were used.

On the right, there is a single delta-wye, causing a 30 degree shift from the 138 system. So from left to right you are 30 degrees out of phase. I believe your choices are to add a transformer, or to do a high speed transfer.

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

I don't think it's safe to assume any phase shifts. Suppose the delta star transformers are Yd1 but connected Yd9. You would need to look at all primary and secondary connections and all the rating plates to get the transformer vector groups before you can even think about drawing a phasing diagram.

Regards
Marmite

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

Marmite,

I don't think we need a phasing diagram to see that it won't phase. Every delta-wye or wye-delta connection will shift by an odd multiple of thirty degrees. Combination of two odds on the left makes an even multiple or zero, against the odd multiple on the right.

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

If your drawing is accurate, the two ends of your "new feeder" are n*30° apart where n=1, 3, 5, 7, 9, or 11.  There is not a wiring change that can solve that problem.  You need one more transformer or you look at open transition transfer.

For fast transfer you can have n be any of those values by selective transformer rewiring, but not 0.  If the new connection would be normally open and used when the normal source is unexpectedly lost, I'd arrange things so that the standby source is 30° lagging the normal source.  That should allow successful fast transfer while the motor bus falls back 30° or a bit more.  Return to normal will be a bit more difficult to achieve, but it can be scheduled and certain motors off-line.

On the other hand, if you need to go both directions equally, I'd pick n to be either 5 or 7 so the motor bus falls back 150° in one direction and 210° in the other direction.

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

Sorry. It's standard power plant configuration and not needed any aditional transformers. Maybe problem  if used
only Y/D1 or Y/D11? I check tommorow primary connection scheme, but from my home archive. Standard power plant configuration and it's work : one RAT transformer 161/6.6kV
and four UAT ( two per generator) 20/6.6kV
work with live transfer w/o any problem. All synchronisation logic on the 6.6kV I provided before two years. See attached
Regards.
Slava

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

Not, Not, I must check, maybe isn't last version of drw.
Seems RAT is Y/Y according to vector diagram.

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

slavag,  look at it this way:  Start at the 138kV grid, go down to the motor bus through T1 & T2 plus T3 and T4.  The motor bus is an even multiple of 30° shifted from the 138kV bus.  If ANSI standard transformers are used the motor bus lags the 138kV bus by 60° but any other even multiple of 30° is possible, including 0.  Now start at the 138kV grid and go through T7 to get to the motor bus.  Now there is an odd multiple of 30° between the two.

There is and always be a phase shift between the two paths unless another transformer is added.

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

Yea , you are right,
now, I would like check my old scheme, maybe I forgot change in the drw RAT to Y/Y or ... after two years forgot something. tommorow at office I check AS MADE drw.

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

I agree with Steven and David on this.
Rewiring will achieve phase shifts in multiples of 60deg.
A wye delta cnnection gives pase shifts in multiples of 30deg.
The T1,T2,T3,T4 group has two wye deltas in cascade, resulting in a simplest case phase shift of 0deg or 30deg + 30deg = 60deg.
Your T6 and T7 transformers are a single stage of wye delta transformation with a phase shift of 30deg. Not compatible.

David, How fast is a fast transfer? I am visualizing something in the order of a cycle or at most one or two cycles. In any event fast enough to complete the transfer before a motor can drop more than a few electrical degrees out of sync.
Anecdotally I had a situation with about 30  30HP propellor fans with two fans on each breaker. When the group was shut down by tripping out the breakers, the pair of motors appeared to circulate the back EMF between them. It would be two or three seconds before the back EMF decayed enough for the contactor coils to drop out.
To the point, with the number of 1000 HP motors involved,I would be cautious of transferring so close to 180 deg out of phase.
However, seeing that a transfer will be done by tripping one breaker and then closing another, rather than an ultra fast transfer on a single set of travelling contacts, I would rather monitor the back EMF and inhibit closing until the back EMF on the bus has decayed to a safe level.
But, is there something about fast transfers that I am about to learn? What I know as a fast transfer is so fast that it is done with a sync check relay.
I would rather pull up 30 deg than take a chance closing on residual voltage at 150deg or 210 deg. You may be close to 200% residual voltage.
Respectfully

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

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

Bill,

I've watched the Beckwith relay do it's thing at one of our plants, where we are also faced with a 30° shift between the two sources and the fast transfer there took about 6-7 cycles (issue trip, confirm open, issue close) and the motor bus fell back about 40°when going from the leading source to the lagging source.  So the motors were about 10° behind the source being connected to.  That was far better than the 19 cycles or so when transferring from the lagging bus to the leading bus and we had to drift back 330° to come into alignment.  Lost a big fan at about 15 cycles.  We will be rewiring a transformer to shift it back 60° so the standby source moves from leading the normal source by 30° to lagging the normal source by 30°.  In our case we will be swapping A and B on the 115kV side and B and C on the 4.16kV side.

The relay that is controlling all of this is watching bus voltage and both source voltages, knows breaker close time, calculates rate of change of phase angle, and issues a close command far enough ahead of desired close point to hit it as close as possible.  In our case the 40° shift in motor bus voltage happens in the fastest possible operating time so we can't do better.

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

David
Thank you for your reply and the time you took to give me a detailed explanation.
Respectfully

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

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

Folks.
I'm so sorry, my home drw was wrong ( copy-paste). I check now my AS BUILD drw's at office, RAT is Y/Y 12. Sorry again.

Fast transfer.Possible, it's work. But it always stress for motors. If used fast transfer in fault time, is O.K. but for maintanance is not so good.

From my point of view better add one Y/Y transformer from 138kV as dedicated RAT ( or standby) connect to one common bus (3'd bus in drw with new feeder red line connection) and from this common bus with two CB's provide connection to each motor BUS in parallel with T3 and T4.
 
Or more simple solution: add new CB from T3 bus to 3'd bus as standby supply.
T3 and T4 feeded from double bus generator bus and of course possible reverse feedeng from 138kV grid.
Regards.
Slava

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

Hey. I forgot something important.
Stars to David and Stevenal.
Best Regards.
Slava

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

Why should a proper fast transfer stess a motor? Aren't you simply starting a motor that already up to speed? It will simply slip until it adjusts to the new phase angle. Seems a lot less stressful than a cross the line start. I'm assuming induction motors. I can see there might be a problem with synchronous motors.

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

Stevenal.
What synch motors used HBT is big problems, once we check this with some German company ( provided such device). Syn motors is in out of step situation and protection must tripped motor.
About stress for the induction motors. In all case you have
phase angle difference and it's reason for some overvoltage on the motor ( not big, but...).
Maybe we need firstly told about terms.
Fast transfer for me is open and close command in the same time w/o any check of CB posotion. It's possible only in case of kvazisynchronasing.
This case is not possible, 30-60deg phase angle isn't kvazisyncronasing.
Our case is 1st phase concidence. David saied about it.
6-7 cycles is good result, in our tested we see also closing command after  300-700ms ( one case was about 1.1sec). you need min 120-150ms for the learn voltage/freq graph. maybe Beckwith relay have another opttion' I don't know. Voltage and freq are decied and in closing time in all cases you have some current pick.
Please see our test reports ( but w/o currents)
Regards.
Slava

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

Stevenal.
Another problems with this type of trnasfer, of course, I say only about manual transfer, not emergency.
1. Pick current will trip infeed.
2. T4 in maintanace and now T3 tripped, all load now on the new feeder, I assume it request some load shedding, after few operations, you would like back supply to T3 or T4, again stress for the system with risk to unwanted trips.
Always with fast transfer you have chance to some fault with stanby or main CB. Is not small power plant, and for my pinion solution must include not only fault condition, maintanance condition too.
At system. was I show, customer used very simple fast transfer. Via main CB contact ( CB open = NC contact) send signal directly to reserve CB close coil ( of course via LOR and additional conditions). Was work about 25years.
Now we provide same logic, but via new digital relys for more safety. Time of transfer about 100-120ms. Think about my feeling, when we tested it. Each down of unit, provided by reverse power trip, system is tested on live.
What I can say, stress for the system, overvoltages/undervoltages, protection starts, tap changer operation etc, once was unwanted trip.
But, is only my opinion.
Regards.
Slava

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