Understand the common way is to have some load sharing unit operating on top of the units governors. The load sharing unit manipulates the governors set-point.

Believe there is a simple way to make a good stable run and firm load sharing without any load sharing unit and no need of governors to talk to each other.

Would like to know is there anything like that already done in the control practice? Mean, generator load sharing to work without any load sharing unit.

 

turpero,

>Understand the common way is to have some load sharing unit
>operating on top of the units governors. The load sharing
>unit manipulates the governors set-point.

The century-old, tried and true method of frequency control for a small "island" load with multiple generators is to put one generator's prime mover governor in Isochronous speed control and the remainder of the prime mover governors in Droop speed control. In this arrangement, trained and experienced human operators are required to monitor the load on the Isochronous unit and adjust the load on the Droop units so that anticipated load changes will not cause the Isochronous unit to try to put out more power than rated nor reduce power output to less than zero (at which point it will likely trip on reverse power). (Yes, that's correct--to adjust the load on an Isochronous machine operating as described above it's necessary to change the load on one or more Droop machines.)

If one thinks about this scheme--they <b>are</b> all communicating, but virtue of the speed (frequency). The Isoch machine maintains the frequency for the grid (including the Droop units), and the Droop units do their thing because the Isoch machine is maintaining the frequency. (It's the way ALL generators and prime movers on any grid operate as long as the grid operators/regulators maintain frequency properly.) This is because of synchronization--all generators operate at synchronous frequency/speed when connected in parallel with other generators. No generator--when synchronized to a grid with other generators and their prime movers--can go faster or slower than synchronous speed (which is a function of grid frequency). If the grid frequency is 50.04 Hz--then every generator synchronized to the grid is running at a speed that is proportional to 50.04 Hz--and no generator(s) can run any faster or any slower the speed corresponding to 50.04 Hz for that generator (which is a function of the number of poles of the generator).

The reason that designers and control engineers like to try to use automated load sharing schemes is that plant managers and operations supervisors don't trust human operators to respond to- and anticipate load changes properly. It's just that simple--the owners/management of such facilities want to rely on automation instead of trained human operators (which cost more money--to train, and to retain). So, these load sharing schemes are used to try to control power generation (frequency) without requiring too much of the human operators. (And as plant operating conditions change over time either because of added load or operational changes these load sharing schemes must also be modified to accommodate the changes--which almost never happens. Or, which "requires" (according to the control system integrators bidding on the upgrade project) a completely new load sharing scheme.

Yes; it's absolutely possible to operate multiple generators in parallel and maintain frequency without some "over-riding" external load sharing system connected to all the generator prime mover governors. That's the way early AC power transmission and distribution systems were operated. But, it takes knowledge and training--for the operators and their supervisors and management--to do so reliably and continuously.

Now, for these automated load sharing systems--they take proper programming and configuration. And that means just take PLC programmer who might be a genius at refinery process control or manufacturing process control and program a power generation load sharing system that works and is reliable and has enough "smarts" to anticipate and respond to unforeseen and occasional odd operating circumstances. It requires someone with a deep knowledge and understanding of power generation and plant operation to even begin to set up such a system. Power generation and transmission and distribution is unique and requires a unique skill set than most PLC programmers have (or even DCS programmers).

AND, as plant operations change and grow--or even shrink--it quite often requires an adjustment to the load sharing scheme. It's not a "set-it-and-forget-it" type of system, unless nothing ever changes after it's commissioned.

In all fairness, there are some load sharing schemes which work quite well in certain circumstances and when properly configured and programmed--but, again, in all fairness, trained and experienced operators keep them working properly (not the technicians--but the operators). They are the exception to the rule in most cases, unfortunately. Most plants limp along with problems (some have fewer problems than others--and most plants seem to have fewer problems on certain shifts or when certain operators are on shift....) and never really do too much to alleviate the problems--mostly because it probably took a LOT of problems and effort just to get to the condition they are currently in and the cost and aggravation to analyze and solve the remaining issues is just too great.

Hope this helps!

 

Looks things in the industry did not change much in the last few years since I've been out of the field.

Few years back did a steam turbine governors retrofit on two units running together islanded from the grid.

Made them sharing load equally and keeping 50Hz fixed as glued. Recently checked with the customer. Still very happy with the performance. They want to do the same with the other units.

It's done just with the governor design itself. No fuzzy logic, no neural networks etc. Just a simple theory behind it and an easy PLC programming.

-without the governors talking to each other;
-without measuring electrical values;
-without any load sharing unit.

Do you think there would be any interest for such design?

Guys that are selling load sharing systems would certainly not be interested !

 

What is the capacity of generation and load in the project you have done for running in islanded mode.

 

The plant has 5 * 15 MW ST generators. Total load moves from 30 to 40 MW. At least three units operating at one time.