Need explanation why gas turbine tripped when generator breaker closed to feed dead grid and the grid only have 3 HV transformer 13kv to 138kv and for more information there is no load connected to the grid only HV transformer.
Without understanding a LOT of details about how the plant and the grid are configured it's virtually impossible to say why.
But, there may be a couple of reasons. First, a unit (gas turbine-generator) has to be configured to power what's called a "dead bus" AND it also has to be configured to be able to accept load(s) AND maintain speed/frequency as loads are added back to the grid.
Second, if there's a possibility that the section of the grid which is now "dead" can be powered from another source while the gas turbine-generator is supplying power to the grid, that source must be capable of synchronizing to the gas turbine-generator so that big arcs and sparks and possible (likely) mechanical damage doesn't occur to one or both generators and their prime movers, not to mention buses and switchgear.
Third, if the section of the grid the gas turbine-generator was powering (even if there isn't any load) must be re-connected to a powered section of grid the unit must be capable of synchronizing to the powered section of grid--again to avoid arcs and sparks and possible (likely) mechanical damage to the generators and their prime movers, not to mention buses and switchgear.
So, there's at least three possible reasons why the gas turbine-generator is not allowed to power a dead bus (unpowered section of grid (transmission/distribution system)).
Can a gas turbine-generator power a dead bus (with no loads, only transformers)? Yes. But, both the gas turbine-generator and the bus have to be designed to allow proper continued operation once the system is restored/re-connected to other parts of the grid.
Hope this helps! Again, without LOTS more information than you have provided it's really impossible to say for sure how and why things are configured they way the are at your site.
Thanks a lot for your help.
The grid which i mentioned as "dead" it can be powered from another source but all the other sources are shut down, the grid containing more than 5 switchgear.
My question is can I remove the protection to eliminate the protection to cause trip or open the generator breaker that I need to feed the grid with, or is that dangerous & risky?
I repeat the grid are dead and all other source are shut down. Only switch gear and transformer on the dead grid.
If the machine is not under warranty and you and the plant owners feel you understand the situation and the risks sufficiently you are free to do whatever you want.
Some of the risks include safety of anyone that might be working on the "dead" 138 kV grid (or distribution lines, if any) if your machine energizes it without their knowledge.
And, in the state described in your first post, the load seen by your generator is going to be almost entirely reactive. Its voltage regulator and protection have to properly deal with that so the machine remains stable.