Can we do synchronize the Generator when the synchronoscope at a point when synchronoscope reaches 10 minutes before 12'0 clock. and what are the draw back for it?

 

Closing the breaker at 10 o'clock is not called syncronizing. It is called manual closing of the breaker only

Any generator need to be syncronized at 12 o'clock for obvious reasons which you may already aware. Some may opt to select close when the scope reaches 11 o'clock if the speed of the scope is fast (humans do have reaction time).
However my advice would be if the scope is moving fast, adjust the speed of the primeover so that the scope turns CW at reasonable speed that would allow the closing to be done exactly or almost to 12 o'clock.

Drawbacks on mal-syncronization could be found by search function in this site or google. Since explaining it would be lengthy, I wish not to do it here.

Good Luck!

 

Thx..
But if u clarify a little bit that will the Gen Circuit Breaker close or not?

If close then is there any negative impact on GCB

 

Whether the GCB would close or not depends on the synchronizing equipment and interlocks made available. Some synchronizing equipment would only allow actual breaker closing at specific intervals (11-1 o'clock) to act as protection. However if there is no such interlocks, my bet would be the GCB would open back itself due to unsynchronism.

As for the impact on the GCB, it would decrease the service interval of the GCB. The impact would be similar to unit tripping at high load. You may refer to your GCB manual for reference. Usually there would be some table or curve on this condition.

How synchronizing is done in your machine? What turbine controller are you using? That information would be useful as well.

 

This was general question.

Normally we follow auto synchronization, Manual synchronization is rare.If we do manual in software MK VI there is monitor function also that is for further safety.

We select monitor and also look at synch parameters and wait for synch permissive are clear and then we will manually close GCB
your are right that ideal position is 11'O clock and protections and interlock are built in for the protection of equipment. So if we want to close before 11' Clock manually GCB will not close in Speedtronic MK VI and other systems.

Why there is limitation actually I want to know that which parameter will disturb? phase angle? angle will be <120 deg.? if < 120deg than wht will it cause? and due to less angle what will be impact on phase (R, Y and B) any two will come closer to each other any phenomenon like cross of wires etc..

Thx for extending co-operation

 

Basically if you can close your breaker out of sync. (Check sync. should stop you from doing this) the minimum you will do is probably damage the breaker and could damage the generator, gearbox or turbine. Do you realise how much torque you are generating when you close out of Synch.?

Why are you trying to Manually Synch. anyway and why are you trying to close at 10 o'clock??

 

you are right that synch check relay will not allow to close CB at this position..

Any ways It was general question.. We are not trying to close at 10 0 clock.

 

Synchronization (manual or automatic) involves several things. Two of the most important are closing the breaker when the incoming and running sine waves are very closely "synchronized" and minimizing the voltage differential between the incoming and running sine waves.

When the synchroscope is approaching 12 o'clock the "slip" (differential) between the sine waves is approaching minimum (slip is zero when the synch'scope is at 12 o'clock) and the voltage differential between the phases is minimal (it's zero when the synch'scope is at 12 o'clock).

Closing the generator breaker with a voltage differential requires minimal mechanical force to close the contacts. If the voltage differential is high the mechanical force required to close the breaker is high.

If the slip is at maximum and the breaker is attempted to be closed the results can be catastrophic and destructive. When the slip is high it means the magnetic forces of the stator and the rotor are opposing each other and if the breaker is closed the rotor will have to rotate the maximum amount to come into synchronism, which is akin to "slipping a pole" which is mechanically very destructive to the generator, the load coupling, and the prime mover.

So, breakers are closed when the slip and the voltage differentials are minimal so that the force required to close the breaker is minimal and the forces in the generator bringing the generator rotor to synchronous speed are miminal.

And this occurs when the synch'scope is at 12 o'clock. But, the command to close the breaker is usually given slightly before the scope is at 12 o'clock because the contacts usually require several cycles to close (as the mechanisms in the breaker are actuated to close the contacts). The idea of sending the command to close the breaker slightly before 12 o'clock is to actually close the contacts at 12 o'clock, which is best for the breaker and for the generator and prime mover and the coupling between them.

Hope this general answer answers the general question.

You can always use your preferred Internet search engine to learn more about the details of synchronization (and get all the vector diagrams and maths)

 

> you are right that synch check relay will not allow to close CB at this position..

> Any ways It was general question.. We are not trying to close at 10 0 clock.

I think I can try to answer the question on behalf of the poster.

There are occasions that the incoming and outgoing frequency cannot be matched sufficiently long to enable the sychro check to conclude that they are running at equal frequency. The problem can be very serious to a point that plant operator may want to take chance to close the breaker at slightly higher frequency (normally outgoing freq).