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.
This interesting case study spotlights the old rule that most great engineering efforts are 80% perspiration (actually, I think it's 90%) and 20% technical smarts. This project simply wouldn't have happened without all that digging, building, and dirt moving.
Great idea. Getting tied into the grid seems to be an important factor here. Saves the whole problem of storage. The perspiration will probably pay for itself in time, since the foundation is the least likely part of this power plant to fail over time.
I agree, Rob, this sure eliminates the storage problem. And it's heartening to read that the minimum for generating hydroelectric power is only a two-foot drop and two gallons per minute. That's a lot less than I would have guessed.
I've often wondered if we could generate power from the creek in back of our house. At least part of the year, it fulfills those minimum requirements.
If renewables are going to make a significant impact, a certain percentage of the power and a certain percentage of the storage will have to happen on the micro level. This is a great effort and it's a perfect example of what can happen at that micro level.
This case study is interesting and a good read. Even though it took a lot of effort and time they are already seeing a return on their investment, which is always a good thing.
average of 40 cubic feet per second flowed through the pond, making it a marginally feasible hydroelectric project
So now everybody is getting all fired up to dump two gallons, let it run down into another bucket, then dump that water back up to the top and expect to make the electric meter run backwards!!
@letsthink: I agree with you that the numbers don't add up. If 40 cubic feet per second of water (18,000 gallons per minute) falling 10 feet generates 20 kW, then 2 gallons per minute falling 2 feet should generate about 1/90,000 as much power, or 0.2 W. Maybe you could make a LED light up with this.
What wasn't clear to me is if they generated single phase or three phase power. Why the three motors? 15hp is about equal to 20kW, so any one motor could have been a generator. Can anyone fill in the blanks here?
Also, I'm curious what prompted the report--it does read suspiciously like an Automation Direct ad....
I agree that there needs to be support and commitment at the micro level. The challenging economic climate of the last few years has definitely fanned the flames of the local movement and a do-it-yourself mentality. Perhaps that will translate into more people attempting projects as ambitious as this one.
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