What are the steps to synchronize while operating on house load


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We have a Gas Turbine (in Frame 6 Mark VI-e control) operating on house load, bearing the load of all the auxiliaries of plant. Now we have to synchronize it with the grid.

We can do it with the line breaker.

What are the steps to be taken to achieve it safely?

The Mark VIe is definitely capable of synchronizing a second breaker, but that requires some additional synchronizing circuit components and usually some kind of "switch" or selector, either on the HMI or on an operator station/console or a generator control panel to activate the additional circuitry and tell the Mark VIe that it's okay to go into synchronizing mode.

There needs to be another PT input from the line side of the tie-line breaker, and some phase-shifting transformer(s) may be needed to account for any step-up transformers 'between' the PT nputs. There also needs to be a discrete input to the Mark VIe to tell it that a second breaker is to be synchronized.

And, about the most important input to the Mark VIe that needs to present is one that tells the Mark VIe to switch from Isoch to Droop mode when the tie-line breaker closes. I've seen this input "forgotten" several times--and it's disastrous.

Presuming all of the required circuitry and components are in place, what you want to do is make sure the house ("island") load is relatively stable and no large motors or loads are going to be started or stopped for a minute or so, and then you want to switch the Mark VIe governor mode from Isochronous to Droop, and then select/activate the second breaker synchronizing function. By switching from Isoch to Droop you are ensuring that the unit will be in Droop Mode when the tie-line breaker closes. (If it's not in Droop mode when the tie-line breaker closes--or immediately after the tie-line breaker closes--you'll find out pretty quickly, and it won't be a happy experience.)

So, to accomplish the task safely there needs to be the appropriate circuitry and inputs to the Mark VIe--or if some other synchronizing equipment is being used it needs to be properly set up, and hopefully tested during commissioning--and you want to be sure that the Mark VIe is either in Droop speed control before you enable the synchronizing circuit OR you want to be sure the Mark VIe has an input to automatically switch it from Isoch to Droop when the tie-line breaker closes.

That should be all that's required.

By the way, it's not possible--nor should it be attempted--to synchronize across a breaker without at least a 25 (Synch Check) relay with appropriate inputs. The results of attempting to synchronize a breaker without the appropriate circuitry can be downright catastrophic--and dangerous to human life.