Normaly this kind of test is called ISLAND TEST because is the operation of the power plant isolated of the Grid and supply only the auxiliary power + eventualy any consumer power (steam or and electricity). You put the unit connect to the grid at FULL LOAD and after you open the grid breaker.

This is a very complicated test for the power plant:

- If is coal, we only can run the power plant may be 30m - 60 m and after you need to trip or increase the load;
- If is a CC then it is possible to run in auto mode and stay in this mode the time that you want bacause the GT control can run very easly to lower loads and you trip the ST runing in BYPASS.

In any case the power plant MUST have the BYPASS SYSTEM (HP and LP pressure, minimum HP).

The power plant control change of LOAD CONTROL to FREQUENCY CONTROL. The test is very hard if the load change = NOMINAL POWER- AUXILIARY POWER is bigger and for coal is much dificult because you need to prepair the coal mils (before put mils operate in half load, because you need to trip imidiatly after the open of the breaker and operate with only one, ...but the minimum power of a coal boiler is 30%-40% nominal, so you need the BYPASS to put the extra steam that you canot put on the ST.
In CC this is much more easly.