Synchronisation of Generator

It depends precisely on how the synchronization process is programmed.

Generally speaking when you are going to synchronize with the grid it provides the frequency control to anything being attached to it, therefore your Master has to have provisions for switching to load control otherwise you will have two controllers trying to maintain a setpoint at a single point.

The result will be hunting as your governor tries to correct the system frequency over which it has no control; i.e., as the grid frequency drifts due to the constant load changes over time, and your Master tries to hold the turbine speed constant, the power angle will constantly oscillate as the difference between the fixed frequency and the grid frequency changes. This will lead to the master swinging between supplying power and absorbing power which is never good for system and/or unit stability.

To answer your question directly, if the Master always has to be in frequency control regardless of what it is synchronized to, then you cannot synchronize to the grid.

In My plant logic designed that when master turbine synchronise with the grid it will goes into load control mode only.I am asking that If Grid source is not available if i want synchronise the master turbine(i.e.,up to now it is in shutdown condition) with the other TG's,then will definitely goes to Freq control that means Load Variations taken by this turbine only.This can be done during start up or not?

This note is not different from RAMCONSUlt's, rather a different angle.

IF I understood the presentation correctly, The controller gets on one input a frequency to sync to. It does not know, where it came from, only that it is present.

It may even have a primary and secondary input. Only the manual can tell, if it so.

To me, it appears, that if Gen.#1 kicks off, #2 becomes the master from then on. When #2 kicks off, the other way around. At least, that is how I would design the logic. The manual will tell for sure.

Your questions are valid. At the same time they cannot be answered without detailed study of YOUR actual control logic, and maybe some tests performed on them to verify your assumptions, deductions.

Having said that, I can tell you, what I would do. It my or may not fit your circumstances.

The grid frequency ought to be the most precise available to you normally. The second most precise can be a quartz generated frequency10e-6 to 10e-8 precision. Normally it is synched to Grid. When the Grid is lost, the quartz maintains it. Upon restoral of the Grid the quartz slowly crawls into phase synch, then interconnect is possible again without fireworks. The frequency input is fed by the quartz all the time, guided by the Grid, or without.

The other possibility is the rude handling in my previous note, where either #1 or #2 can assume Master. There the restoring of the Grid connection have to rely on the old time honored methods. I would design it that way, but the manual has the final say.

What is Meant by Quartz Generated Frequency?

Quartz generated frequency means that the governor has an internal crystal oscillator timebase that provides a very precise 50/60 Hz signal that is used when there is no other reference/source to control the prime mover speed; i.e., a generator operating in stand-alone or island mode.

This is what tells your Master to operate at synchronous speed regardless of its load, up to its rating of course. All of the other machines in your island will then use the Master as their frequency source for synchronization and load following.

The timekeeping accuracy specification of 10^-6 to 10^-8 means, that losing the Grid synchronisation 10⁺⁶ to 10⁺⁸, meaning 1 million to 100 million 50HZ cycles will pass before a single cycle is lost or gained. Closer in importance is the phase loss degree to the presumed preciser Grid. That assumption is yet to be verified.

1 sec=50 cycles, 1 million cycles = 2x 10⁺⁴sec = roughly 200min = about 3 hours to lose or gain or not at all a full cycle.

Multiply these numbers by 100x for 10^-8 precision. It means 300 hours to gain or lose a full cycle. That is over two weeks.

If the Grid does not return in a very small fraction of that time, you have some real problems to fret about.

here your question is not clear...in your plant two generators are synchronize with system grid... or only two generator are used to deliver the power for load...it should be clear....the frequency is taking referance and terminal voltage also taking referance for synchronize the generators...according to that we do parallel operation...on power plant...

Only two generators are in parallel.If master generator tripped then another one goes into freq control.If I want to sync the Master turbine with the running TG,as per logic it will definitely goes to Freq control immediately after sync.Can I do that or not?

I think language is getting in the way here. In the West the word "can" generally means permission, yes or no. As others have stated, that is based on the logic designed into your control system, and seems to be confirmed by your own observations.

Perhaps you are asking if it is advisable or suitable. That depends upon what you see, if the transfer is smooth with no effect on operations then it is working ok for your particular situation.