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Last time we saw how the involute profile of spur gear teeth ensures smooth contact between gears when they rotate. Today we’ll see why it’s important to be able to change the rotational speed of the driven gear in relation to that of the driving gear by modifying their gear ratio, the speeds at which gears move relative to one another. Why would we want to modify the rotational speeds of gears relative to one another? One reason is to compensate for the fact that alternating electric current (AC) motors drive most modern machinery, and these motors operate at a fixed speed determined by the 60 cycles per second frequency of electricity provided by the utility power grids of North America. By fixed speed I mean that the motor’s shaft revolves at a single, fixed rate. It can’t run any faster or slower. This is fine for some motorized applications, but not others. Basic machinery such as wood cutting saws, grinders, and blowers function well within the parameters of the AC motor’s fixed speed, because their working parts are intended to rotate at the same rate as the motor’s shaft. As a matter of fact, in this instance there’s often no need for a gear train, because the working parts can be connected directly to the motor’s shaft, and the machinery will be powered and function correctly. There are many instances however in which a fixed speed does not match the speed required for more complex machinery to correctly perform precise, specialized tasks. Take a machine tool meant to cut steel bars, for example. It has a rotating part meant to cut through the steel during machining, and to properly do so its cutting tool bit must turn at 400 revolutions per minute (RPM). If it turns any faster, the cut won’t be smooth and the tool bit will overheat and break due to increased friction. If the AC motor driving the machine tool turns at 1750 RPM, a common speed for such motors, then the tool bit will be turning at a much faster rate than the desired 400 RPM, and this presents a problem. To solve the problem we need only add a gear train between the motor and the part containing the tool bit, meaning, we must connect the gear train’s driving gear to the motor’s shaft and a driven gear to the part’s shaft. But in order for this arrangement to work a conversion must take place, that is, we must design the gear train to operate at a specific gear ratio. By gear ratio, I mean the speeds at which the two gears will rotate relative to one another. Next time we’ll introduce the gear ratio formulas that make it all work.
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Posts Tagged ‘electric utility engineer’
When Do You Need To Modify Gear Ratio?
Wednesday, February 19th, 2014
Power Plant Inefficiency
Sunday, September 22nd, 2013|
Last week we identified some inefficiencies in our water to steam power plant energy cycle. The superheater addressed some of these concerns, but not others. Our illustration discloses one of these wasteful areas to be coming from the turbine exhaust. That’s energy laden steam being expelled into the surrounding atmosphere! It’s the same heat energy that was produced in the boiler when water was transformed into steam. It came from burning fuels like coal, natural gas, and oil, all expensive and precious natural resources.
In its present configuration the power plant will work, but because steam is being continually dispersed into the atmosphere, it must continually be replenished. The key ingredient, water, must be drawn into the power plant from a nearby source, treated for contaminants, then fed into the boiler to make up for lost steam. That wastes both water and energy, because the make-up pump, which draws water from the lake for treatment, (thus “making up” for spent water), is continuously operating, resulting in excessive wear and tear and increased operating costs. Fortunately, power plant engineers have devised methods to correct these inefficiencies. They’ve come up with a clever means of recapturing exhaust steam, thus enabling it to recycle within the system. Next week we’ll see how this is accomplished with a piece of equipment called a condenser.
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Coal Power Plant Fundamentals – “Big Coal”
Sunday, February 27th, 2011|
We’ve been talking about coal fired power plants for some time now, and it’s always good to introduce third party information on subject matter in order to gain the most from the discussion. What follows is an excerpt of an interesting book review on the subject of coal consumption which appeared in the New York Times: There is perhaps no greater act of denial in modern life than sticking a plug into an electric outlet. No thinking person can eat a hamburger without knowing it was once a cow, or drink water from the tap without recognizing, at least dimly, that its journey began in some distant reservoir. Electricity is different. Fully sanitized of any hint of its origins, it pours out of the socket almost like magic. In his new book, Jeff Goodell breaks the spell with a single number: 20. That’s how many pounds of coal each person in the United States consumes, on average, every day to keep the electricity flowing. Despite its outdated image, coal generates half of our electricity, far more than any other source. Demand keeps rising, thanks in part to our appetite for new electronic gadgets and appliances; with nuclear power on hold and natural gas supplies tightening, coal’s importance is only going to increase. As Goodell puts it, “our shiny white iPod economy is propped up by dirty black rocks.” To read the entire article, follow this link: http://www.nytimes.com/2006/06/25/books/review/25powell.html?_r=2
A locomotive crane unloading coal from railcars at a power plant in the late 1930s. Next week we’ll continue our regular series, following energy’s journey through the power plant. _____________________________________________ |
