clean power generator questions

[tsteahr]

In fact there is only one generator in the whole American power system that controls the frequency. All the other run in "droop". In other words their contribution to grid is proportional to the grid frequency. If the grid is slower they contribute more power and vice verse. Therefore the grid might run slightly slower at high load and slightly faster at low load. The number of periods/per day is maintained exactly the same every day.

That is interesting. I had never heard that before. Do you happen to have a link I could read more about that?

I have never heard any mention of one generator being a "master" and all others being a slave. There are baseload units and peaking units, but that is relative to total power output to the grid, not frequency.

I work at a station with two large nuke units. I have never heard of either acting as a master frequency unit. All generators come off line from time to time for maintenance. With nukes, it is generally every 18 months. So if there was a "master" generator I would think this task would have switch from baseload unit to baseload unit over time. Of the 7 nuke units I'm familar with daily operation, I have never heard of any being designated as a master.

If you have any more information I'd like to read it...

 

[Chilly807]

In fact there is only one generator in the whole American power system that controls the frequency. All the other run in "droop". In other words their contribution to grid is proportional to the grid frequency. If the grid is slower they contribute more power and vice verse. Therefore the grid might run slightly slower at high load and slightly faster at low load. The number of periods/per day is maintained exactly the same every day.

I was wondering that myself, without compatible interconnected governing systems throughout the country (read impractical), there's no way to effectively load-share, unless you use speed droop.

Any thoughts on how many separate grids there are through the US and Canada? I suspect there's a LOT, considering the localized outages and small utilities that feed local customers.

I think I'll see if I can get a straight answer out of Miller's tech people about acceptable frequency and voltage requirements for the welder I have. It may shed some light on why I get sketchy results running on the generator.

Clean power is definitely desirable, but where do they draw the line as to what's acceptable and what isn't? I suspect it'll be a blanket statement, something like, "Poor quality of supplied power may adversely affect the service life of your welder."

Sean

 

[Redneck in training]

There is only one generator that maintains its speed against precise frequency standard. It runs in Isochronous mode. All the other generators (running in Droop mode) compare their speed that follows the Isoch generator also with precise frequency standard. If the Isoch generator starts slowing down due to loading the Droop generators increase power contribution to the grid. When the Isoch generator speeds up the Droop generators decrease their power contribution to the grid. The Droop control loop is strictly proportional. In other words one generator (usually the biggest one) maintains the grid frequency all the other maintain power.

http://www.canadiancontrols.com/documents/technical/Speed Droop and Power Generation.pdf

Clarification about droop and frequency control

Google "Droop control"

 

[tsteahr]

There is only one generator that maintains its speed against precise frequency standard. It runs in Isochronous mode. All the other generators (running in Droop mode) compare their speed that follows the Isoch generator also with precise frequency standard. If the Isoch generator starts slowing down due to loading the Droop generators increase power contribution to the grid. When the Isoch generator speeds up the Droop generators decrease their power contribution to the grid. The Droop control loop is strictly proportional. In other words one generator (usually the biggest one) maintains the grid frequency all the other maintain power.

http://www.canadiancontrols.com/documents/technical/Speed Droop and Power Generation.pdf

Clarification about droop and frequency control

Google "Droop control"

Interesting links. Thanks.

But the September 17, 2009 post indicates the opposite of what I understand you to be saying. I don't see any indication that one generator (presumably a nuke baseload unit) is operated in isochronous mode, while all others are in droop mode. It seems when many units are operated in together as in a grid, droop mode is used to control the prime movers. It seems isochronous mode is used when one generator is driving a load independently.

I can't see it being physically possible for one generator, regardless of size, to operate slightly faster then every other on the grid.

 

[Redneck in training]

Interesting links. Thanks.

But the September 17, 2009 post indicates the opposite of what I understand you to be saying. I don't see any indication that one generator (presumably a nuke baseload unit) is operated in isochronous mode, while all others are in droop mode. It seems when many units are operated in together as in a grid, droop mode is used to control the prime movers. It seems isochronous mode is used when one generator is driving a load independently.

I can't see it being physically possible for one generator, regardless of size, to operate slightly faster then every other on the grid.

They all run at the same speed. What happens at high load is that the Isoch generator starts slowing down. Since the Droop generators have the same reference speed SP as the Isoch they see the dropping of the speed and start contribute more to the grid. Needles to say the speed (frequency) change is fraction Hz only. In 5% droop 1% drop in frequency will increase power of the droop generator by 20%.

Isoch mode is used only in so called island grid. In example a refinery generates its own power. Some fertilizer plants also run in Island mode.

 

[Chilly807]

They all run at the same speed. What happens at high load is that the Isoch generator starts slowing down. Since the Droop generators have the same reference speed SP they see the dropping of the speed and start contribute more to the grid. Needles to say the speed (frequency) change is fraction Hz only. In 5% droop 0.1 Hz will increase power of the droop generator by 20%.

Part of what's missing here is the fact that by increasing the speed reference of one or more of the droop generators, you in fact do not actually increase the bus frequency, as long as there is a larger isoch generator on line, unless the droop generator is capable of carrying all the load on the bus. Instead it will increase it's carried load as the speed reference is raised.

We have both types of systems at my work, that is, both droop and isochronous load sharing. The droop system uses hydraulic governors, the isoch ones use either a digital control or electronic control over a hydraulic actuator. The isoch systems use a set of auxiliary contacts on the circuit breakers to allow the individual controls to "talk" to each other and thereby share load.

This would be a good topic for a whole new thread, we're a long way from the original topic of clean power requirements..

Sean

 

[tsteahr]

They all run at the same speed. What happens at high load is that the Isoch generator starts slowing down. Since the Droop generators have the same reference speed SP they see the dropping of the speed and start contribute more to the grid. Needles to say the speed (frequency) change is fraction Hz only. In 5% droop 0.1 Hz will increase power of the droop generator by 20%.

Isoch mode is used only in so called island grid. In example a refinery generates its own power. Some fertilizer plants also run in Island mode.

That makes more sense. The base load plants I'm familiar with all run at full power (about 4500MW thermal) regardless of grid conditions (unless there is a major grid disturbance or environmental issue). None are run in load following mode although their design could accommodate it. Makes sense that load following plants (peaking units) have to run in droop.

Perhaps many/all base load plants (not just a single one) are run in isochronous mode? That would make more sense to me.

Sorry for the thread derail, but I can't help myself...

 

[Redneck in training]

That makes more sense. The base load plants I'm familiar with all run at full power (about 4500MW thermal) regardless of grid conditions (unless there is a major grid disturbance or environmental issue). None are run in load following mode although their design could accommodate it. Makes sense that load following plants (peaking units) have to run in droop.

Perhaps many/all base load plants (not just a single one) are run in isochronous mode? That would make more sense to me.

Sorry for the thread derail, but I can't help myself...

Ofcourse the Droop control can be disabled and the contribution of particular generator can be kept constant. It, in essence, means that the steam inlet valve is held at constant position.

 

[wrooster]

This would be a good topic for a whole new thread, we're a long way from the original topic of clean power requirements..

Just 4 pages to go from contemplating running a welder from a small gas-powered generator to discussing grid synchronization of 1500MW nuclear-powered steam turbine generators. I love this place!

Wrooster

 

[Redneck in training]

Back to the topic then. I think that the ability to run the welder depends on ability of the generator to maintain frequency, voltage and power factor.
I also think that the power should be without voltage spikes that could damage the equipment. The power should be ideally pure sine wave but since that is not usually the case the power should be symmetrical to prevent heating up of transformer units. If the power is asymmetrical there a DC component that can burn a transformer. All the above is obvious.
I personally would select rather larger generator to have some power reserve. Inverter generators are still fairly new. In theory they should be better than standard generators because of speed of the elctronics.