SYNC CHECKING (machine rotating opposite to system)
SYNC CHECKING (machine rotating opposite to system)
(OP)
here's the scenario what would you expect to see?
a sync check relay monitors phase-phase voltage on both the incomming and running system. the incomming system is wired incorrectly with two of the generator wires crossed.
because of the crossed wires electrically the machine is rotating opposite to the system.
what would the single phase voltages look like at the sync relay? would you ever be able to match speeds and make the sync check relay think the system was actually in sync?
or would the single phase vectors still be going in opposite directions and not allow the sync relay to see a matching speed.
a sync check relay monitors phase-phase voltage on both the incomming and running system. the incomming system is wired incorrectly with two of the generator wires crossed.
because of the crossed wires electrically the machine is rotating opposite to the system.
what would the single phase voltages look like at the sync relay? would you ever be able to match speeds and make the sync check relay think the system was actually in sync?
or would the single phase vectors still be going in opposite directions and not allow the sync relay to see a matching speed.






RE: SYNC CHECKING (machine rotating opposite to system)
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SYNC CHECKING (machine rotating opposite to system)
RE: SYNC CHECKING (machine rotating opposite to system)
Any single phase sine has two components; one positive and one negative. I think that a single phase sync relay will have a problem telling the difference between two voltages with same frequency and amplitudes if there is no phase information. The positive component in V1 will match the negative component in V2, and vice versa. I think.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SYNC CHECKING (machine rotating opposite to system)
it may be advisable ( when auto sync are used) to use another check synchro relay to monitor proper operation of the auto sync one.
in such scheme the CS relay setting ( U,f, phi)window is including the one from the auto sync.
It should prevent the event you describe to occur ( if consider that wirings are different)
RE: SYNC CHECKING (machine rotating opposite to system)
A detailed pe-synch test is needed to verify proper connections, proper rotations, etc. to prevent the damgea that could occur.
RE: SYNC CHECKING (machine rotating opposite to system)
Best way to check is to disconnect the links at the generator and backfeed both sides, then you should read in phase at synch check and scope. Feed-forward works too if you can isolate your system and close synch breaker.
RE: SYNC CHECKING (machine rotating opposite to system)
With a phase reversal it is not possible to have three phases in sync but it is possible to have one phase in sync.
respectfully
RE: SYNC CHECKING (machine rotating opposite to system)
whats confusing is if you look at the vector quantities of the line and running 3 phase (phase to phase) voltage the vectors rotate in the opposite directions. so when you look at any individual leg of this graph it appears as though the phase-phase line and phase-phase bus voltage could never come into sync because they would cross each other 120 times per second at 60 hz.
i think what i've determined and the important point to remember is there is no rotation on single phase. so two single phase sources feeding a sync device will only match speed (HZ) and could care less about rotation.
RE: SYNC CHECKING (machine rotating opposite to system)
In practice, you have two single-phase voltages with no phase information. You can not tell if it is rotating CW or CCW, nor can the relay. So, when both have the same frequency, amplitudes and phase difference is zero - the relay thinks it is OK to close the breaker.
That's why I never seen a single-phase relay in my life. I think.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SYNC CHECKING (machine rotating opposite to system)
Here is the chance to change that, on the screen at least:
http:/
The KAVS is one of the commonest check synch relays out there. It is adequate for ensuring two systems can be paralleled safely once they have been commissioned and rotation proven by other means.
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: SYNC CHECKING (machine rotating opposite to system)
When we have synch lights and synch scopes on a manual panel, I try to keep them on separate phases. A good operator would notice the lights going out at 4:00 or 8:00 instead of 12:00 and hold off closing the breaker.
Some old time diesel generator panel designers use three lights and a synchscope, with one light across each phase of the synchronizing breaker. The bright/dim flashing pattern of the lights indicates phase sequence and in-synch conditions and frequency match.
Good job catching the phase swap before it became a problem!
RE: SYNC CHECKING (machine rotating opposite to system)
I needed that refresher.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SYNC CHECKING (machine rotating opposite to system)
From my point of view, it's not important what is a connection to synch check relay.
Are possible both of them: phase to phase or phase to earth.
Important: correct connection to relay and test before synch.
For some "safety" we are prefer used phase to phase voltages.
For big generator prefer used two phase to phase or three single phase voltages.I think it's also requrements in US.
For HV lines many times we are used single phase voltages synch check, becouse on line usally we have only one single phase VT on phase S (L2, B).
More from that , for connection block of gen-trafo w/o gen CB in the old system used on line side single phase voltages and on generator side phase to phase voltages.
Regards.
Slava
RE: SYNC CHECKING (machine rotating opposite to system)
1. With generator breaker open, energize from system. Check all meters for expected rotation.
2. With system isolated from utility further upstream, start generator and close breaker. Check meters for expected rotation. Check syncroscope and synchronizing relay for zero voltage on the monitored phase across the closed breaker.
RE: SYNC CHECKING (machine rotating opposite to system)
I was always led to believe that the check synch element normally has a time delay.
If there was a serious problem (eg reverse rotation) wouldn't the check element be only picked up for a very short time and not time out, therefore the check contact would not close ?
RE: SYNC CHECKING (machine rotating opposite to system)
Take a three phase circuit and split it into two branches. Connect each branch to a side of an open breaker but on one side swap phase B and C compared to the other side. A is opposite A, B opposite C, and C opposite B. Now apply a single phase sync check relay on phase A. The relay will see zero volts difference and locked phase, after all there is a direct connection between A and A. But you wouldn't want to close the breaker. Sync check on the second or third poles of the breaker would never permit closing.
Now split the branch and connect both branches to separate sources. There is no reason that the previous condition could not be repeated.
It is absolutely essential that it be proved that both sources are rotating the same direction before using single-phase sync check relays.
RE: SYNC CHECKING (machine rotating opposite to system)
I agree that a single phase check relay would not pick up incorrect phase sequence - I wouldn't think that a check synch device is meant to check wiring is correct.
However the part I still don't understand is even if one side had an incorrect phase sequence, wouldn't the A phase vectors be rotating in the opposite direction to each other if the generator is rotating in the wrong direction, thus only in synch for a very small period of time - much lower than the time delay.
PS - I might be talking about something different, rotation can mean phase sequence ??
RE: SYNC CHECKING (machine rotating opposite to system)
Yes, you are talking about something different. Rotation in this sense does mean phase sequence. B follows A, C follows B. With only one phase, there is no rotation in this sense. The voltage increases and then decreases and then increases again, mathematically according to a sin function. I goes up and down because something is rotating (a generator rotor), but this is a different rotation.
RE: SYNC CHECKING (machine rotating opposite to system)
RE: SYNC CHECKING (machine rotating opposite to system)
You may be thinking of the two components, one rotating in positive direction and the other in negative direction, that I mentioned in the beginning of this thread: "Any single phase sine has two components; one positive and one negative. I think that a single phase sync relay will have a problem telling the difference between two voltages with same frequency and amplitudes if there is no phase information. The positive component in V1 will match the negative component in V2, and vice versa. I think"
A much simpler way of seing it is how jghrist says: " With only one phase, there is no rotation in this sense. The voltage increases and then decreases and then increases again, mathematically according to a sin function. I goes up and down because something is rotating (a generator rotor), but this is a different rotation"
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SYNC CHECKING (machine rotating opposite to system)
RE: SYNC CHECKING (machine rotating opposite to system)
As I understand from original posting you try to sync two lines together with one rotating in different phase order So lets say You have L1,L2,L3 system at your side and L1',L2',L3' as incoming. Switch L1' and L3'( or L2' whatever is easier) and it should solve your problem with the rotation. I am writing this because I believe you have to connect primary and backup system to a pump (motor) and you want to have it turning in same direction all the time. I had similar problems, but I solved them in a few minutes doing that. You actually don't need to ask generator to switch its phase shift do it on your side. That will change the way of rotation and save you big thinking.....
P.S. If you have single phase rotation in wrong direction switch neutral and phase wire positions.
RE: SYNC CHECKING (machine rotating opposite to system)
"However the part I still don't understand is even if one side had an incorrect phase sequence, wouldn't the A phase vectors be rotating in the opposite direction to each other if the generator is rotating in the wrong direction, thus only in synch for a very small period of time - much lower than the time delay." -- DiscoP
In our situation we were actually reading Vab on the incoming bus and Vac on the running bus. (should have been Vab and Vab for both) So if you were to put both of these systems at exactly 60 HZ and look at the vector diagram Vab and Vac will never come together for any period of time. Because the incoming was rotating ABC and the running was rotating ACB.
It seems to me that if both speeds were actually matched these voltages would be 180 degrees out all of the time. Much like what was said earlier one would be positve and one would be negative.
If anyone is interested what actually happened here is we had a contractor swap some underground cables for us. They crossed the phases when reinstalling the new cable. We phased check across the open disconnects to the substation. This phase check was done wrong. We were doing some pre start checks on the turbine and noticed 3 motors rotating in the wrong direction.
So here's a second question to spur some discussion. If performing phase checks across open disconnects. What needs to be done to verify proper phasing on two systems that are not rotating at the same speed? I do know the answer to this one as we did this correctly the second time.
RE: SYNC CHECKING (machine rotating opposite to system)
RE: SYNC CHECKING (machine rotating opposite to system)
It's always difficult to measure if systems are in phase with disconnects open. What you need to do is actually close the disconnects, then feed either back from the utility or forward from the generator. (of course isolating the other system) Then take measurements at all devices involved for rotation and synch. The sych check should be happy, the scope at 12 o'clock voltages match etc etc.
RE: SYNC CHECKING (machine rotating opposite to system)
I worked it out while in the shower last night - this is the place where most of my thoughts come together !
Generators produce sine waves - not vectors.
If you work with a mathematical tool for too long, sometimes you start to think they are real !
RE: SYNC CHECKING (machine rotating opposite to system)
But still, the models describing all these things are very real and very valid. So, you shouldn't have a problem either way you look at it.
Isn't it funny how the shower brings out thoughts? If you don't sing...
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SYNC CHECKING (machine rotating opposite to system)
RE: SYNC CHECKING (machine rotating opposite to system)
For initial check-out, the easiest way to confirm matching phase rotation is to energize the same piece of equipment from each source, one at a time and check rotation there. Another way to check is to take two voltmeters, one across A-phase of both sources, and one across B-phase of both sources. If both meters are bottoming-out and topping out together as the sources come into and out of phase, your phase rotations match. This is easier to see using Simpsons, but works with digital meters as well.
Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep engineers away from customers, romantic interests, and other people who can't handle the truth.
RE: SYNC CHECKING (machine rotating opposite to system)
Instead of voltmeters it was once common to use tungsten lamps. This is the real old fashioned way of doing things - many old plants still have synchronising lamps as a fallback to the auto synchroniser. There are variations of the theme which use three bright lamps to indicate synchronism or two lamps of equal brilliance and one dark lamp to indicate synchronism. With a little practice it is possible to have as good a synch as the auto system would give.
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: SYNC CHECKING (machine rotating opposite to system)
GenSwgrEng , you are right 100%.
I think we need add to GenSwgrEng post, post of Stevenal and
GTstartup ( what need for commissioning) and we have best and short manual for design and commissioning teams.
I would like only closed several small points.
1. Synchrocheck relay used for permanent source ( dU, dF and dFreq) or as voltage check ( U1>U2 and U1> Umax and U2<Umin or U1=U2=0 (dead bus-dead line)or other same options). For voltagecheck functionality prefer add VT MCB OK signals or/and dead source CB or Dis are open.
2. Synchrocheck used as additional check point after synchronazing relay for two rotate source. Series connection or DualChannel syncronazing relay.
RE: SYNC CHECKING (machine rotating opposite to system)
Your post we also must add to this manual.
it's old but work w/o any problem up today.
RE: SYNC CHECKING (machine rotating opposite to system)
"Another way to check is to take two voltmeters, one across A-phase of both sources, and one across B-phase of both sources. If both meters are bottoming-out and topping out together as the sources come into and out of phase, your phase rotations match. This is easier to see using Simpsons, but works with digital meters as well"
RE: SYNC CHECKING (machine rotating opposite to system)
This is only bullet proof if you can measure the primary voltages. If you are measuring PTs this is a disaster waiting to happen.
RE: SYNC CHECKING (machine rotating opposite to system)
- i agree and this is what we did using two sets of high voltage sticks and high voltage meters.
RE: SYNC CHECKING (machine rotating opposite to system)
Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep engineers away from customers, romantic interests, and other people who can't handle the truth.
RE: SYNC CHECKING (machine rotating opposite to system)
1) Break the connection at the generator and close the synch breaker.
2) Verify zero potential between generator and bus PT inputs for each phase (A and C)both at the auto-synchronizer and synch check relay.
3) Reconnect the generator (after opening the synch breaker of course)
4) With the generator rotating and excited, connect lamps between the bus and generator PT inputs for each phase at the auto-synchronizer.
5) If the lamps go bright and dim together, my rotation is correct.
Have I got it covered?
Thanks,
Gatorsoft
RE: SYNC CHECKING (machine rotating opposite to system)
Your step 5 is ok, but my preferred method is to wire the lamps A-A', B-C' C-B'. Synchronism is indicated by a dark A lamp and equal brightness on the B and C lamps. It is easier to detect equal brilliance than it is to detect a true dark condition, unless you switch off the lights in the substation. If wired per your proposal the lamps appear dark for a fairly broad phase angle near the point of sychronism. You must use identical lamps and make sure they are rated for double the line-neutral voltage.
----------------------------------
Sometimes I only open my mouth to swap feet...