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Synchronization Questions
3

Synchronization Questions

Synchronization Questions

(OP)
We are going to commission a 600V double ended switchgear with N.O. tie and all synch and control logic will be initiated by a Universal Relay: GE C60. I have some confusion when it comes to the Synch-check function settings of this relay which are:

-Synchronization max voltage difference
-Synchronization max angle difference
-Synchronization max frequency difference
-Synchronization max freq hysteresis
-synchronization dead source select
-synch dead V1 source max voltage
-synch dead V2 source max voltage
-synch Live V1 min voltage
-synch Live V2 min voltage

I read the GE manual for these descriptions and still doubtful. Does anyone had any typical settings for these functions or at least educate me a bit on them?

How does the terms LiveV1/LiveV2, DeadV1/LiveV2, DeadV1/DeadV2, DeadV1Xor(exclusive OR)DeadV2 and deadV1/deadV2 relates to our transfer/re-transfer scheme.

Our switchgear transfers via open-transition and re-transfers via closed transition.

Thank you and hope there are also GE folks here.

RE: Synchronization Questions

Are you tying feeders together for increased capacity or are you sync'ing a generator?  

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

RE: Synchronization Questions

It all sounds pretty straight forward.  The settings seem to say what they are/what they do, other than I'm not sure about the dead source select.  Ask a specific question or two rather the very broad brush approach you have so far.

RE: Synchronization Questions

(OP)
Waross, the double ended switchgear is fed from two identical power transformers having a capacity to handle the entire switchgear load. During closed transition re-transfer or closed transition MANUAL transfer, the two transformers are temporarily paralleled to attain a "make-before-break" incomer-tie operation.

Sorry about the broadness davidbeach. V1 and V2 as I undrestand is related to source 1 and source 2 voltages respectively.

I am confused at the reason of having these LiveV1/LiveV2, DeadV1/LiveV2, DeadV1/DeadV2, DeadV1Xor(exclusive OR)DeadV2 and deadV1/deadV2 settings and what are they being used for.

Appreciate any enlightenment from those who encountered this.

RE: Synchronization Questions

Will you accept a guess? From the settings available this sounds like a universal relay that is also suitable for sync'ing a generator as well as well as checking the conditions across a tie breaker. (Frequency difference and phase angle)
As well as sync'ing with the grid to do a closed transition, a standby generator must be allowed to close into a dead bus.

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

RE: Synchronization Questions

(OP)
Yes it is a universal GE relay.

At what max phase angle and max frequency difference do we typically set inorder to allow two supplies in parallel.

In some readings, I read:

phase angle difference = 15 Deg.
frequency difference = 0.1Hz
maximum voltage difference = 5% nominal

I would like to understand the basis of setting this so.

By the way, the LiveV1/LiveV2, DeadV1/LiveV2, DeadV1/DeadV2, DeadV1Xor(exclusive OR)DeadV2 and deadV1/deadV2 settings conditions where the breakers are allowed to be closed and bypass the synch process.
 

RE: Synchronization Questions

Is this two supplies from two utility sources or a utility source and a generator? I would treat the two differently.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Synchronization Questions

Frequency difference only applies to completely different systems. (Usually grid and generator). If both your feeders come from the same system the frequency must be the same.
Phase angle mostly aplies to generator sync'ing.

By the way, the LiveV1/LiveV2, DeadV1/LiveV2, DeadV1/DeadV2, DeadV1Xor(exclusive OR)DeadV2 and deadV1/deadV2 settings conditions where the breakers are allowed to be closed and bypass the synch process.
If either feeder is lost, the breaker must close into a dead bus, unless you determine that you do not want to "Pick up" a dead bus.

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

RE: Synchronization Questions

(OP)
ScottyUK, the two feeds are coming from upstream double ended switchgears which are further connected to a primary switchyard supplied from two line sources coming from the same utility...there are no totally separate generator source.

Waross, since there no completely separate source in this system, does this mean that the I may set the frequency difference at minimum say 0.01Hz...the present setting is 0.1Hz

The max. phase angle difference between the two sources were proposed to be set at 15Deg. I would like to get educated as to the basis of this setting...with my application, can I set this lower?
 

RE: Synchronization Questions

2
Hi Nightfox1925.
You also need know: what is Dead and what is a Live voltages.
For example, 0.75Un is Live and 0.25Un is Dead.
Maybe it's same trafo's, but not same tap position
in the Live /Live you will have dU. Standard setting is 5%
Phase Angle, as saied below is separate source issue, but possibel case two types of load on the trafos.
In the not separate sources 15deg is more or less standard setting, in case of separated sources abot 7-10deg. All depend. please take in account dPhi, dU and dFr used only for Live/Live option, for the Dead /Live only max and min voltages.
Best Regards.
Slava
 

RE: Synchronization Questions

(OP)
Thank you slavag. Any other comments is highly appreciated for my reference.

RE: Synchronization Questions

(OP)
If there is a large motor connected to it and say both transformer taps are at nominal. On the motor starting study, it was figured out that bus A with the tie open, the voltage dip caused by motor starting is 0.84P.U. for 3.5 seconds.

I am looking on either setting the U/V pickup for the transfer operation to be 0.80P.U.with a time delay of 3 seconds

or

set the U/V pickup for the transfer operation to be 0.85P.U. with a time delay of 5 seconds (>3.5sec starting time). Is this going to be acceptable?

 

RE: Synchronization Questions

Hi.
If I understood you right?
You try choice setting for the changover between bus A and B ( bus-tie close) and avoid multransfer in case of start motors.
It's depend on your system. Actually transfer is start not from 0.85-0.8Un, you can start from 0.75-0.7Un and shorted your transfer time to 1-1.5s. from other hand, is possible put setting 0.8Un, but with time about 4-5s ( not so good solution).
This data more for MV buses, but from my point of view, is valid for LV system too. Of course, in the first case need check time of protection operated for avoid transfer in case of SC on the LV buses.
Hope that help.
Best Regards.
Slava.

RE: Synchronization Questions

(OP)
Thanks Slavag,

If you guys won't mind me asking.

What is purpose of having a Live Minimum Voltage and Dead Maximum Voltage settings?

I am actually also trying tho relate this application with our secondary selective switchgear with normally open tie control logic.

RE: Synchronization Questions

Live minimum voltage: To prevent transfer on voltage dips.
Dead maximum voltage: To prevent closing into residual voltages.

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

RE: Synchronization Questions

Synchronizing systems are made to tie systems together one of which varies ( like a generator). I doubt that two utility systems vary from each other.
There may be a fixed offset in the voltage ( caused by differnet upstream transformer configurations )usually a 30 degree offset.  The offset could come and go as the upstream system is switched but you would never see a variable phase difference.
If they are offset, forget about paralleling them.
If they are not, parallel away,but don't forget to check the Fault current in paralled operation.  

RE: Synchronization Questions

That's not strictly true BJC, it's quite possible to get some pretty significant phase differences between unloaded and loaded circuit which are nominally in phase.

Probably the most striking example I've seen of this is a generator unit aux transformer fed from the generator terminals and a station aux transformer fed from the grid which can feed a common bus. The phase difference which exists when the generator is flat out is surprisingly large - over 20° - with the GSU transformer reactance being the major source of the shift. Closing the breaker can result in some unusual load conditions: power flows via the UA transformer to the station bus and then out onto the grid via the SA transformer.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Synchronization Questions

echnically true Scotty.  but how fast did they change relative to each other?
If they  are on the different likes back to the same source and load is causing one to be differnet I don't want to be around when you tie them together.

RE: Synchronization Questions

Absolutely real - it sometimes confuses the operations techs and results in a sleepy engineer wandering in to site in the early hours to resolve it. I only got around to measuring the phase shift because the first time it happened to me I was starting to question if the protection relay blocking breaker closure was behaving properly. I was quite surprised at the time, but having sat and roughed out the calcs it made sense.

The two sources weren't changing relative to each other at all at the time: frequency was locked to the grid, and the phase angle was dependent on the generator load. The turbine has to be backed off to about 30% load to get the phase angle permissive from the check sync relay, then can load up again after breaker closure.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Synchronization Questions

Hi.
Scotty's example it's a good example in the lot of power stations, where is SAT or RAT fed common bus with minimum load. Many times we see events "in Sincheck", "out syncheck".
In case of block trip all load of UAT bus will trnsfered to the common bus within 120-130ms with break before make, no problem.
In one case with paralleled two trafos ( same sources) with phase difference more than 20deg and on another taps (about 3-4taps difference), was reactive current, but not some dangerously. It wasn't mistake, was test of option in case if one trafo in oveload situation.
Best Regards.
Slava

RE: Synchronization Questions

(OP)
Thank you very much for all your contribution. I am actually reviewing the transfer and re-transfer logic programmed inside the C60 relay and I'll keep everybody posted.

By the way, this seems to be an awfully dumb question but I will go on with it anyways just to clear my head:

What do you mean by Phase Undervoltage Dropout on undervoltage relay terms? I know what U/V pickup means but how about this?

RE: Synchronization Questions

Hi Nightfox.
The same terms. You use U/V pickup term, it's more North American term, in IEC world we more use term U/V start or IEC symbol U< or U<< start.
BTW, C60 for LV board? Why not some smart relay or small PLC? I'm not against, intresting why.
Best Regards.
Slava

RE: Synchronization Questions

(OP)
Hi slavag, for some awkward reasons, the client specs specified it. I know this C60 is for Bay Controllers but that is how ridiculous things are sometimes being done on this part of this world.

RE: Synchronization Questions

OK.why I asked, becouse  we provide now design of changeover system for LV board with MV bay controller too. Instead PLC/UV relays/synchrocheck relays, etc. .
I see, not only we, is good smile.
Good Luck.
Slava  

RE: Synchronization Questions

(OP)
Slavag, I got an update as to the why?

The C60 controller (IED) is a PLC wherein the synchronization and the transfer/re-transfer scheme can be programmed into a logic inherent to the relay. This will in turn, saves cost of wiring, interposing relays, U/V relays etc.

RE: Synchronization Questions

(OP)
Hi slavag,

I have read through a spec from the client.

It states that the transfer will occur if the voltage drops to 85% Nominal (0.85 P.U.) with a time delay of 3 seconds. The voltage on the other bus should be >90% nominal to allow transfer.

I don't think 3 seconds is enough to dissipate LV motor starting. However, I taking plans to determine the starting time of the highest rated motor connected to this 600V switchgear to verify whether the U/V time delay is sufficient or not.

Does this mean that the U/V element (in the G.E. lingo: AUX U/V OP) connected to the bus PTs should be set at 90% nominal (0.9 P.U.) and have this BUs U/V element block the transfer?

The other settings will be:

Synch Dead Maximum Voltage: 0.25 P.U.

Synch Live Minimum Voltage: 0.75 P.U.

By the way, I forgot to inform that V1 and V2 are voltage on the sources and are connected to the line PTs. The bus PTs are connected to the C60 relay's Auxiliary Voltage input.
 

RE: Synchronization Questions

Hi Nightfox.
"It states that the transfer will occur if the voltage drops to 85% Nominal (0.85 P.U.) with a time delay of 3 seconds. The voltage on the other bus should be >90% nominal to allow transfer."

From our expirience 0.85Un for 3 sec it's very sensetive setting. From other hand, maybe is OK.
What is a very importanr point: are you client have re-start system for the motors? For example in our project, we have finished transfer in 1.5sec max, after 2sec...I have found new country for living smile.

"Does this mean that the U/V element (in the G.E. lingo: AUX U/V OP) connected to the bus PTs should be set at 90% nominal (0.9 P.U.) and have this BUs U/V element block the transfer?"
Yep, you are right, we used term "normal voltage".
setting for the LIVE and DEAD for my pinion is best choice, from time to time we use 0.3Un.

Connection is OK. additional Q's what is a procedure of your transfer, As I understand it's break before make, but what do you block with "fault voltage" on the second BB, break or make?
Best Regards.
Slava




 

RE: Synchronization Questions

(OP)
The transfer procedures are as follows:

Manual Transfer - Closed Transition
1. Initial conditions: 52-1, 52-2 closed, 52-3 open
2. Select "Trip 52-1"
3. Close 52-3, synch check verifies, logic checks for any
   transfer blocks, protection blocks etc.
4. 52-3 closes, 52-1 instantaneously trips.

Manual Re-Transfer - Closed Transition

1. Initial conditions: 52-1 open, 52-2 closed, 52-3 closed
2. Select "Trip 52-3"
3. Close 52-1, synch check verifies, logic checks for any
   transfer blocks, protection blocks etc.
4. 52-1 closes, 52-3 instantaneously trips.

Auto-Transfer - Open Transition

1. Initial conditions: 52-1, 52-2 closed, 52-3 open
2. Phase line 1 U/V operates (V1<0.85 for 3 seconds)
3. 52-1 trips
4. 52-3 closes
 

RE: Synchronization Questions

Hey. We are in synchronasing smile.
"
1. Initial conditions: 52-1, 52-2 closed, 52-3 open
2. Phase line 1 U/V operates (V1<0.85 for 3 seconds)
3. 52-1 trips
4. 52-3 closes
  "
We provide point 3 only in case of "noraml volatge" ( part of 52-3 ready, no trip, truck inserted, control voltage OK, no protection trip and BB voltage OK)
Regards.
Slava

RE: Synchronization Questions

(OP)
Thanks slavag,

One thing more, if the 27 pickup is set at 3 seconds before it will start initiating an open transition transfer, what will be a typical total time delay being set before it initiates 52-3 to close?

On closed transition transfer, if 52-1, 52-2 and 52-3 are closed, what would be an typical time delay to be set before the bus tie (52-3) trips open?  

RE: Synchronization Questions

(OP)
To all,

How much time will it take for a residual voltage to dissipate?

RE: Synchronization Questions

The decay of residual voltage from motors depends mostly on how fast they slow down. It depends to a lessor extent on motor design and the connection of capacitors. Many motors will have lw enough residual to reconnect after 5 to 10 seconds.
BUT, there are serious exceptions. For example, in a sawmill, large motors driving high inertia loads such as band mills, chippers, or hogs, and having capacitors connected to the motor leads can still have dangerous residual voltages after a minute or more if they are left to run down on their own without some type of braking.
If the motor contactors are opened, you may transfer safely but do not attempt to restart the motors until the residual voltage has dropped to a safe level.

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

RE: Synchronization Questions

Hi Nightfox.
Possible a few options.
1. Residual voltage connection.
52-1 opened status--Bus voltage below 0.4Un ( for example, we have boards with 0.5Un)-->52-3 close command.
Of course you need check restart current of all motors for avoid ins. overcurrent trip, or provide some load shedding.
2. Residual current connection with motor contactor status
52-1 opened status--Bus voltage below setting--all motor contactors are openeed----> 52-3 close command
In case of 1 and 2 you dont need any timer for 52-3 close command
3. Long time close command---after 10sec, for example, you don't check ( only 52-1 opened status) voltages---> 52-3 close command, it's special case, but used.
As Bill saied, residual voltage decay time on the motor bus it's very dependly value. up tp 10sec or more, if it's number of fans.
Becouse this, you need continusly monitoring of residual voltage and not timer.
Hope that help.
Best Regards.
Slava

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