We realized that, as a grid-tied induction-based generation system, the generator/motors would freewheel if the excitation current from the grid were lost. The grid acts somewhat like a battery being charged, providing a degree of needed resistance to the generators.
If grid resistance were to disappear because of a power failure, the generator/motors could spin up to twice as fast as designed. We needed the ability to shut down our hydroplant automatically in case of a grid power failure.
The control panel contains an AutomationDirect DirectLogic 05 Micro Brick PLC, a C-More HMI panel, I/O, and associated components.
The turbine has an integral control gate to adjust water flow from 0 percent to 100 percent. This control gate was designed to be opened and closed by a 12-inch double-acting hydraulic cylinder, so the first piece of automation equipment installed was a Parker Oildyne 24V DC hydraulic reversible pump to operate the gate.
The power for the pump and all the low-voltage control circuits is supplied by two deep-cycle 12V batteries which are connected to two 12V battery charger/maintainers.
When a shutdown signal from the control panel or a fault condition occurs, the shutdown procedure is simply to run the pump in the “close” direction for 60 seconds and open the contactor to the generators. The hydraulic pump has a built-in pressure relief valve that allows it to run safely a minute or two after maximum extension or retraction of the cylinder.
It was crucial that the system also monitor rpm and shut down based on either overspeed (caused by a disengaged generator or broken belt) or underspeed (insufficient power generation) conditions, so it was time to install a programmable logic controller.
I decided that, though it was AutomationDirect’s smallest PLC, a DirectLogic 05 Micro Brick PLC (pictured above) would be sufficient. In October 2007, I ordered our first PLC, a proximity sensor to count shaft revolutions, a NEMA 1 enclosure, and various pushbuttons, terminals, DIN rails, and wire ducting. After a couple of weeks of learning ladder logic and playing around with the PLC, I began to install the basic automation system.
A local bearing distributor determined what belts, sheaves, and shafts were needed to transfer rotation of the turbine to the three Baldor induction motors. Though generating electricity with induction motors is not unusual, a system of three identical motors running from one turbine seems to be unique. Initial tests in February 2008 confirmed that this would work. All three motors properly synchronized when coupled by the belt drive. Within a week, the first kilowatts of power were generated.
My admiration for all the hard work and ingenuity!
Here in Michigan (and in most states I would think) the DNR would be all over this. Also FERC (Federal Energy Regulatory Commission) claims jurisdiction and requires that a hydro have a license even with the tiniest stream generated electricity if it is grid interconnected. These two entities would easily double the cost of the project even at this small scale. I would like to know how you avoided these burdens.
A lot of people have trouble conceptualizing the induction aspect of a motor/generator. An induction machine delivers the nameplate rated hp as a motor at the nameplate rated amount of slip below synchronous rpm and, in turn, will generate the rated equivalent electricity as a generator at the same amount of slip above synchronous rpm. An electric motor is not "synchronized" at start up - that is just the condition under which it delivers maximum torque because it is at maximum slip. The line sets the voltage, frequency and phase relation. The induction machine simply uses those properties to operate without need for complex controls, regulation and phasing.
...try again with the watts to horsies...as one horse is 746 watts...so a 15 horse motor would be around 10 KW....
Article says 3 of the 15 horse motors...so yes...about 20KW...if all goes well.
Then, to get the buy-back...I'm assuming the generator must be exactly 60 Hz...?
I've worked at a couple small (30-40) Mega-watt Bio-Mass plants...the on-line syncro is extremely important...and...I'd assume this set-up here in the article has at least a transfer switch of some kind...? That is one of the first things any hydro or PV set-up requires. Otherwise I would think you could end up with utility power running your motors and pumping the water backwards...but then, I could be wrong....
If I can get 20Kw from 2 gallons a minute falling from 2 feet, I can easily pump it back up again with little ornamental pool pump, which uses less than 250 watts, so I will have 20250 Watts to sell back to the utility.
I dont even need a stream !
The story was talking about 40 cu ft per second, dropping 10 feet, which is 18,000 gallons per minute, or equivalent to 90,000 gallons per minute dropping 2 feet as opposed to the 2 gallons in the opening paragraph.
I also read the article in the Automation Direct publication. and I found it fairly interesting. I can certainly imagine that there would be a whole lot of government people wanting to have control over exactly how it was done.
The method of using standard induction motors driven a bit faster than synchronous speed was quite interesting. I can understand needing to have some belts that could slip, as a means of allowing the motors to synchronise with the mains power, because otherwise it would not work. It is also probably the cheapest approach, although it may not be the most efficient. My choice would be to drive three phase alternators and then convert the power to the correct frequency using a switching cycloconverter. That is more costly, however. The advantages are that one single device could be controlled to deliver the desired amount of power, and the generator would not need to have the drive speed controlled so precisely. Besides that, I like alternators more.
One interesting thought is that one of the older mecanical meters could be driven backward quite simply, but the newer generation of smartmeters could easily be programmed to not run in reverse. In addition, It is certain that the power company could pull all kinds of tricks with the smartmeter programming.
One last comment is that it would be interesting to see a detailed description of both the mechanical and the electrical design of the system.
Jim, I agree. That's mind-boggling. But here in California, for decades PG&E fought solar power in homes tooth and nail. A once-famous local columnist, Herb Caen, once famously said "PG&E wants to put a switch on the sun." When PG&E finally had to give in, it then fought buy-back for many more years.
What part of free is so tough to get? I think it's actually about control, not about free.
Ann- I just made a similar query related to “power buy-back” in today's article describing low-cost Solar PV’s.Hit this link: Same issue. Not legal in Florida.
Froese beware. The term "environmental impact" in the 21st century is NOT related to a technical assessment or common sense. "Environmental impact" is a legal and political term that is based on a maze of disjointed, over bearing, and convoluted laws, regulations, and policies writen by some clueless folks, supposedly with good intensions. The majority of the enforcers are egotistical morons who have a basic policy of 'deny/reject all applications unless unless forced to approve them".
To be clear-
1. We need to protect and care for our planet.
2. Some of the 'enforcers' are very competent and diligent.
3. We need a single set of intelligently integrated [and understandable] laws and regulations with a workable enforcement mechanism.
My favorite 'bonehead policy' relates to petroleum- [oops-way off topic]
Choice A-extract it from the earth in the US using the best companies, under the best supervision, using the best workers, creating the most domestic jobs, with the least chance of environmental damage.
Choice B-the current hypocritical, 'head in the sand' policy of exporting US dollars to pay countries who are not 'environment friendly' to extract petroleum, sometimes using marginally competent workers who 'do not spill much'. Petroleum is then placed into a leaky tanker that travels 1000s of miles to unload it in the US.
"It is easier to ask forgiveness than permission." Seriously, the environmental impact is minimal since the lake has been there for 100+ years, and there was already a spillway here. Regarding utility interconnection and net metering, our state (South Carolina) does not have rules and regulations for this yet and our local electrical co-op was actually quite helpful and generous in this regard. I'm quite certain that if we had to fulfill all the environmental, engineering, seismic, etc. regulations California has, this project would have been a "no go."
The main belt (from the turbine shaft to the secondary shaft) is toothed, but the belts to each individual motor/generator are ordinary v-belts. We have found that the slippage allows them to synchronize. On rare occasion, when starting starting a generator after other(s) have been running for sometime, it can be 180 degrees out and cause the breaker to trip, but most of the time they seem to sync up by themselves in a fraction of a second.
Froese, thanks for taking the time to respond to my question. You have done something I wish to do, although my application would be a pelton wheel system since I have fairly low flow but a 900 foot head.
It looks like you took the time to research the highest efficiency in belt power transmission- are all your drives toothed belting? The video is not clear--the main drive from the turbine looked like it might be a multiple v-belt setup but the motor drives certainly looked like toothed belt drives. Do the toothed belt drives on the motors allow for automatic synchronization of all three motors with each other? Did you have to play with the shaft orientation on each motor to get all three sinewaves from the motors to coincide?
Congratulations on your efforts! You can be justifiably proud of your accomplishment. And I probably will investigate Automation Direct as well!
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