Auto Synch capability difference between Black Start and Non-Black Start units

This question is on behalf of my Plant Manager, and is directed to any 7EA plants with MK V that has had GE modify your controls for black start operation.

Our site has 8 units, 4 are black start capable and 4 are not.

We have what I think is a curious side effect on the 4 units with the controls modification, and I have been unable to get GE to comment as to whether this effect was by design or just the way the particular GE TA programmed our units.

On our non-black start units, we have the ability to select auto sync mode at any time during the start-up.

On our black start units, auto sync mode can't be selected until the unit has reached 95% speed. (basically FSNL)

I am interested if anyone else with the black start modification has this same limitation?

I have my own opinion as to whether you should or should not select auto sync earlier in the start-up process.

My main question isn't if you should or shouldn't, but rather can you on your black start units?
There is black start and there is dead-bus breaker closure. Often the two are necessary to re-energize some line or portion of the grid, but one can be used without the other.

I would ask if there is some difference in the dead-bus breaker closure logic that is responsible for this difference. Or, posit that the programmer who wrote the logic may not have had the entire definition of when and how it should be possible to initiate Auto-Synch.

Another possibility is that if there is a Synchronizing Selector Switch (typically referred to on electrical schematids as 43SS) on the front of the Generator Protection Panel that many times when it is in the OFF positioin, it is really in the REMote/OFF position. And, when the turbine control system Master Control is set to REMOTE (or CABLE REMOTE, or SERIAL REMOTE or HARDWAIRE REMOTE) and the Synchroniing Selector switch is set to the REM/OFF position the unit will automatically initiate the Auto synch process as soon as it gets to FSNL. (Usually, when the Synch Selector switch is in OFF and the turbine Master Control is in AUTO the operator is required to take some manual action to enable synchronization once FSNL is reached, either Auto or Manual synch).

So, one of the things to consider, besides is there something which is being done differently when black start is selected and enabled, is do you really want the unit to Auto synch immediately when it gets to FSNL--AND will the unit be always synching to a live bus or a dead bus, or is there some logic signal (contact/discrete) input which tells the turbine control system if the bus it will be synching to is dead or live? Do you want the operator to at least know if the bus the unit is synching to is dead or live?

I haven't seen your specific scenario, but I can imagine it could happen. As far as a "standard" from GE, well, that's another story best left for another time. Let's just try to figure out how your plant could be operated, the various possible modes and bus status conditions, and then put together some kind of matrix to use to describe what the operator should do--or what you want GE to modify so that it operates the way you need it to operate. But, this latter is best done after fully understanding all of the possible scenarios that can be experienced at your plant, what the management wants to happen in each scenario, and then work from there. (This may have been done at the time the black start mod was planned, but it's also possible that GE didn't get the message or missed something. So, if there are records around of that specification, best to have those to refer to in this study of what can happen, what could happen, and what should happen.)

Hope this helps!

It would be great if you could write back to let us know how you progress on this issue and its resolution.