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






RE: Synchronizing (2) feeders that are out of phase with each other
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
RE: Synchronizing (2) feeders that are out of phase with each other
RE: Synchronizing (2) feeders that are out of phase with each other
RE: Synchronizing (2) feeders that are out of phase with each other
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
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
RE: Synchronizing (2) feeders that are out of phase with each other
RE: Synchronizing (2) feeders that are out of phase with each other
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
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
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
RE: Synchronizing (2) feeders that are out of phase with each other
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
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
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
RE: Synchronizing (2) feeders that are out of phase with each other
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
Yours
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Synchronizing (2) feeders that are out of phase with each other
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
RE: Synchronizing (2) feeders that are out of phase with each other
RE: Synchronizing (2) feeders that are out of phase with each other
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
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
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
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
RE: Synchronizing (2) feeders that are out of phase with each other
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
RE: Synchronizing (2) feeders that are out of phase with each other
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
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
RE: Synchronizing (2) feeders that are out of phase with each other
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
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
If I'm still lacking any info...I made this Visio drawing that should be fairly easy to update.
RE: Synchronizing (2) feeders that are out of phase with each other
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
RE: Synchronizing (2) feeders that are out of phase with each other
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
in your drw.
Regards.
Slava
RE: Synchronizing (2) feeders that are out of phase with each other
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Synchronizing (2) feeders that are out of phase with each other
I agreed.
Regards.
Slava
RE: Synchronizing (2) feeders that are out of phase with each other
What else do I need?
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?: 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
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
Regards
Marmite
RE: Synchronizing (2) feeders that are out of phase with each other
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
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
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
Seems RAT is Y/Y according to vector diagram.
RE: Synchronizing (2) feeders that are out of phase with each other
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
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
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
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
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
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
Stars to David and Stevenal.
Best Regards.
Slava
RE: Synchronizing (2) feeders that are out of phase with each other
RE: Synchronizing (2) feeders that are out of phase with each other
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
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