Synchronization Questions 3

[nightfox1925]

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.

 

[waross]

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

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

 

[davidbeach]

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.

 

[nightfox1925]

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.

 

[waross]

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

 

[nightfox1925]

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.

 

[ScottyUK]

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


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

 

[waross]

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

 

[nightfox1925]

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?

 

[slavag]

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

 

[nightfox1925]

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

 

[nightfox1925]

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?

 

[slavag]

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.

 

[nightfox1925]

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.

 

[waross]

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

 

[BJC]

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.

 

[ScottyUK]

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.


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

 

[BJC]

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.

 

[ScottyUK]

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.


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

 

[slavag]

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