Operating Under AGC Control

Hi,

My GE gas turbine unit is going to be under AGC control which means that setpoints (4-20ma) are coming from grid control center to my unit every 4 seconds.

My question is that AGC doesn't know about some unit conditions like fuel pressure, thermocouple temperature, some special vibration of unit and which I consider when I assign new setpoint locally to my unit. I mean I check every conditions before assign new setpoints to the unit but AGC doesn't.

So is there any risk for unit trip under AGC control?

loghman,

If this is a GE-design Frame 9E (or Frame 9EA) heavy duty gas turbine with a Mark* turbine control system and DLN-I (Dry Low NOx 1) combustion system, then, Yes. There are things which the grid company/operator should be (but usually AREN'T) aware of when operating the unit using AGC.

If the gas turbine has conventional (diffusion flame) combustors, then, no; there really isn't anything the grid company/operator really needs to be aware of.

Generally, in a combined cycle power plant the steam turbine is considered a "follower" turbine. That means the power produced by the steam turbine is a function of the gas turbine exhaust temperature and exhaust flow-rate. Even if there are auxiliary (or "duct") burners in the HRSG producing the steam using gas turbine exhaust for the steam turbine there usually isn't any real "control" of the steam turbine load once the plant is on-line. If the GT load (and exhaust temperature and -flow-rate) change, then usually the ST load will also change. (Most combined cycle steam turbines get to a certain load/operating point after the generator breaker has closed, and then the steam turbine control valves go fully ("wide") open--and whatever steam is available from the HRSG is converted to power. So, <i>usually</i>, the grid company/operator doesn't have control of the steam turbine via AGC. They probably have a load signal from the ST and the GT and they just have to be aware that when they change the GT load the ST load will most likely also change. And, they have to adjust the GT load to make the total plant output (GT plus ST) equal to whatever they want the total plant output to be.

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