[mbreese]

Power plants need to be connected to other sources so their AC frequencies can be in phase. If the multiple AC waves were out of phase, you’d cause all sorts of issues. It wouldn’t surprise me if the cogen plant was designed to only work in concert with external power, but not in place of it.

Emergency power would be expected to work independently of mains power.

[the_real_sparky]

True for inverter based generation (most renewables like wind and solar), but generally not for rotating machines like most Co-gen plants. Some rotating machines (steam turbines generally) won’t have governors for frequency control, but usually in a CHP plant they would have a linked combustion turbine that does. Rotating machines that are paralleled with the rest of the grid are by default in sync with all of the other rotating machines if there is not some sort of fault situation at the plant or on the grid. If you try to parallel a generator with the grid that is out of sync (frequency or phase), the grid will always win and pull the generator into sync (potentially destructively for the generator).

The most likely limitation of a typical power plant operating disconnected from the grid would be if it could “black start” or not. Cogen plants would normally have this capability. Essentially the problem is whether you have enough power available from backup generation to bring all of the plant auxiliary systems online and get the generators initially started and producing power. Once started you set the governor to maintain 60.0Hz (if in North America) and begin slowly bringing on load so you can ramp the generation to match it.

The easiest solution to a future blackout would be to match the load in your island area to the output of your plant and then disconnect from the rest of the grid before or at the time the blackout occurs. This way you have avoided the black start situation completely. The blackout detection, disconnection, and load balancing steps can be automated to occur nearly instantly if the system is designed well.

The main issue for Berkeley is that the cogeneration plant doesn’t seem to be sized to accommodate their islanded load. This is especially problematic if you lose a generator while islanded because then you will have instant frequency collapse if you were already on the edge of your plant’s capabilities.