Sir.

Is there any effect of GT output by DWAVLBA-(Calculated power in site condition) in frame 6 gas turbine control by mark v.

 

Sir,

This sounds like some kind of "Megawatt Reserve" function. Megawatt Reserve is a means for holding some megawatts "in reserve" by limiting output. If there is some kind of need (say frequency disturbance) then the unit can respond with a few "extra" megawatts.

So, by definition, if the function is active then maximum power is limited (so as to hold some power "in reserve").

I think the jury is out on whether or not this function works as advertised at all times. And, if I understand how Megawatt Reserve works (and I've only seen a cryptic description of the function), then it can "miss" high or low on determining what maximum load is (for the purposes of calculating some reserve) and therefore either not hold very much power "in reserve" or hold too much power "in reserve" (the latter limiting power output more than "desired"). I have no personal experience with this function, nor do I know anyone who had worked with it, and I don't have any example of the sequencing/application code to review.

But, based on my understanding of Megawatt Reserve (if that's what you're referring to) I'm reasonably certain that most owners and operations personnel would not be pleased with the operation when it was put into service as it would limit, and sometimes incorrectly so, power output at Base Load. (Most owners and operations supervisors--and the bean counters they work for, in particular--don't like anything that limits power output unless they are contractually required to do so, and even then they still don't like it!)

 

MW reserve as you refer to is popularly known MW spinning reserve capacity. Talking about this reserve, specifically in power generation, we have to differentiate between what we wish to have and what we are required to have. If our generators do not require to provide spinning reserve capacity by the order of not less than 5%, then we should be thankful. It is a gift. Standard Grid Codes in any country will definitely stipulate this requirement to ensure the grid works the way it works.

Many people take for granted that matching supply and demand for a grid system is as simple as turning the power up and down. In reality it is not as simple as that. The main reason is even the grid dispatchers do not know when a 50MW steel mill is going to draw current from the grid. Therefore there is only one way to do it right i.e. by mean of iteration. Yes, most of generators if not all that connected to a grid have to do continuous iteration process that has executable time step as short as 4seconds to match supply and demand and to preserve the grid frequency at its scheduled frequency.

What happens if we want to iterate a 10000MW demand by the time we have only a 9900MW reliable running capacity? It won't take long, probably no longer than 3 minutes the grid under frequency load shed (UFLS) protection will trigger to remove the demand load by at least 100MW. That 3 minutes is quite short to synchronize another generator anyway. Or without UFLS protection the entire grid will collapse very soon due to under frequency + under voltage failure. To ensure iteration can be done at all time, therefore at any time the grid dispatchers shall ensure adequate spinning reserve capacity has to be made available and the mechanisms that perform such iteration process namely governor speed droops and AGC (Constant frequency) mode are in working order.


General equation for determination of minimum spinning reserve requirement for a grid system is as follows:<pre>
APSRC = P_max + FRR + DFE

Where

APSRC = Active power spinning reserve

P_max = The biggest per unit capacity of the prime movers attached to the grid

FRR = Frequency control & regulation requirement

DFE = Allocation for demand forecast error.

All parameters in this equation are in MW</pre>

 

why would somebody need a megwatt reserve function when any unit (GE or not) could be run in speed (aka droop) mode?

 

In our GE machines we have spinning reserve of 15MW. Is this spinning reserve and the other one which you mentioned are the same? When the machine is synchronised, it goes to 15MW immediately.

I want to know why the machine has to go to 15 MW immediately after synchronising.

Thanks,
johny

 

Because some operators can't be bothered operating a machine, so their supervisors want everything to be automated so the operators won't screw up?

 

> why would somebody need a megwatt reserve function when any unit (GE or
> not) could be run in speed (aka droop)mode?

This question probably has to be addressed by others. Somehow let me try to provide general explanation. It may or may not true for GE control system.

When we operate our GT under exhaust temperature limiter the GT output will become an independent variable. As long as you get the limiting exhaust temperature you can't decide its output. Your controller knows the safe limit to feed the fuel so that the exhaust temperature limit will not be violated.

When we operate under droop mode the output will become an independent variable. The exhaust temperature may change according to GT output. If we don't have mean to limit the maximum output that the GT can deliver without violating exhaust temperature limit, then this limit will be exceeded. Therefore we need special function to calculate the maximum GT output that yields the maximum allowable exhaust temperature. As you know the maximum GT output corresponding to the maximum allowable exhaust temperature is dynamic. It changes with ambient air temperature, pressure, humidity and so on. Unlike exhaust temperature limit.

 

No. It is not. If reliable capacity of your GT is 100MW and you load it at 85MW, then 15MW (100-85) is the spinning reserve that we refer to.

In your case, based on your info, most likely the controller, or the default load set point has already been set to bring the load to the minimum allowable stable generation.

There are two reasons that I know why you should bring the load to a save minimum immediately after synchronizing.

1. Assuming you synchronize your generator at 50 Hz frequency. The fuel supply is throttled so that it is just enough to rotate your turbine generator at 50Hz but produces zero output. If system frequency goes up, the droop will reduce fuel supply in and attempt to damp system frequency from further increases. As a result the fuel supply is less than the amount required to rotate the turbine generator at 50Hz. Since your generator has already synchronized to the system it wishes to continue to rotate at 50Hz. Therefore it draws current from the system (motoring). A moment later it trips on reverse power protection. To protect against this possibility it is important to bring the load to a safer minimum immediately after synchronizing,

2. Some governors or even prime movers are not very stable to operate at very low loads.