Introduction to NEMA motors

                                     Approximately 90% of all industrial applications use three phase induction motors. Why? The standard utility service is three phase, 60 hertz. It is the most practical motor for uses requiring over five horsepower. Special mechanical or electrical features for unusual conditions can be readily incorporated into a three phase induction motor.

The purpose of this home study guide is to familiarize you with AC motor fundamentals and motor terminology.

                                    AC motors are used all over the world in residential, commercial, industrial and utility applications, and U.S. Electrical Motors manufactures a wide variety of these motors for a wide variety of applications.

                                     A thorough understanding of this material will give you the ability to select and price the right AC motor for you or your customer’ s application. We hope that you find the format of this course user-friendly; it has been designed to provide you with simple, straightforward answers to your AC motors questions.Motor development began in the 1800’ s with Oersted and Faraday’ s research on magnetism, and Sturgeon’ s development of the electromagnet in 1825. Davenport received the first patent on an electric motor in 1837. By 1890, AC generating stations came into being, but many diverse routes were being taken at this time. Edison was working in his Pear Street station – on DC.

The city of Manhattan was on DC, Niagara Falls was generating at 25 cycles, California at 50 cycles, and Philadelphia was utilizing two phase power.

National Electrical Manufacturers’ Association (NEMA).NEMA will be referred to frequently in this course; they have established standards for a wide range of electrical products, including motors. NEMA is primarily associated with motors used in North America. The standards developed represent general industry practices and are supported by the motor manufacturers. These standards can be found in NEMA Standard Publication No. MG-1.

source:http://electrical-engineering-portal.com

New bendy device could power wearable electronics!

People on a busy sidewalk use lots of energy to get from one place to another. But some of that energy gets wasted. Shoes and the pavement absorb this mechanical energy. What if that energy instead could be put to better use?

“Harvesting mechanical energy is vitally important for wearable and portable electronics,” says Zhong Lin Wang. He’s a materials scientist at the Georgia Institute of Technology in Atlanta. A person’s phone, for instance, might be powered by their own movements. But first researchers have to figure out a way to gather that energy.

Sangtae Kim had an idea about how to do that. He’s a materials scientist at the Massachusetts Institute of Technology in Cambridge. He and his colleagues have come up with a way to use chemistry to convert wasted energy into electricity.

Their invention is similar to a battery. A battery has two electrodes, made from different materials. Between them sits a liquid or solid material called an electrolyte. When the battery is connected to an electric circuit, a reaction inside the electrolyte creates particles with an electrical charge, called ions. Those ions move from one electrode to another, through the circuit.

In the new device, the electrodes are made of the same material, a mixture of lithium and silicon. And they’re flexible. The electrolyte is sandwiched between them. As the device bends, it compresses the electrode on one side. At the same time, the bending stretches the other electrode. The uneven stresses make ions flow.

“Once we bend the device, lithium really wants to move to the other electrode,” says Kim. But it can only pass through the electrolyte in the form of lithium ions. “So lithium will separate into an electron and a lithium ion,” Kim explains. “And then lithium ions will move from the compressed electrode to the one that is stretched. Those lithium ions have a positive charge.”

The process leaves a lot of lone electrons, each of which has a negative charge. Those electrons want to join up again with the positively charged ions. However, they can’t move through the electrolyte. Instead, the electrons flow through wires that connect one side to the other. That movement is an electric current, and it can power a device. “The flow of electrons is the electricity,” Kim explains.

When the electrons reach the other electrode, they recombine with the lithium ions. That results in neutral lithium atoms.

The device unbends when the pressure is released. Now there’s again an imbalance between the two electrodes. So lithium ions travel back to the uncompressed electrode. And electrons flow through wires to rejoin them.

“This process basically repeats and repeats in reverse directions” as the device is bent and unbent, says Kim. His team reported its work January 6 in Nature Communications.

The inspiration

Kim got the idea for his team’s new invention after reading about a “smart road” project in Italy. That project used the mechanical energy from cars passing on the road to make electricity. It did that with piezoelectric (PEET-zoe-eh-LEK-trik) materials. These are crystals that produce an electric charge when pressure deforms their structure.

Piezoelectric devices work very well with a high frequency of mechanical energy, Kim notes. Those frequencies might range from 20 to several thousand times per second. However, the type of smart road project Kim read about is not yet very practical, he says. The reason: Costs for the equipment would be high. And especially if a road doesn’t have a lot of constant traffic, little electricity would be produced.

Kim’s approach instead harvests energy with chemistry. And it works best with actions that take place more slowly. “It doesn’t have to be regular motion,” he notes. “It can be any slow motion.” For instance, it could be something like walking at a rate of two steps per second.

The ions move relatively slowly in the new method. And that may be one reason why it works well with low-frequency actions, notes Wang, who was not involved in the research. However, he adds, piezoelectric and other types of energy harvesting devices also can work with a range of low to high frequencies.

The new technology “still needs some engineering breakthroughs” before it becomes practical, Kim says. The output from the prototype is only one microwatt per square centimeter. That’s less than a thousandth of the energy needed to light a typical LED light bulb.

Despite the challenges, Kim thinks the technology could one day power personal electronics or run a smart home. Maybe a sidewalk application could even add power to the electric grid.

“Someone might say it’s ambitious, that but that’s sort of the goal that we’re working towards,” Kim says.

Source- www.sciencenewsforstudents.org

Four-stroke engine cycle produces hydrogen from methane, captures carbon dioxide

                 

Georgia Tech professor Andrei Fedorov (left) and an undergraduate research assistant Yuzhe Peng are shown with the laboratory-scale hydrogen reforming system that produces the green fuel at relatively low temperature in a process that can be scaled up or down to meet specific needs.

Credit: Candler Hobbs, Georgia Tech

When is an internal combustion engine not an internal combustion engine? When it's been transformed into a modular reforming reactor that could make hydrogen available to power fuel cells wherever there's a natural gas supply available.

By adding a catalyst, a hydrogen separating membrane and carbon dioxide sorbent to the century-old four-stroke engine cycle, researchers have demonstrated a laboratory-scale hydrogen reforming system that produces the green fuel at relatively low temperature in a process that can be scaled up or down to meet specific needs. The process could provide hydrogen at the point of use for residential fuel cells or neighborhood power plants, electricity and power production in natural-gas powered vehicles, fueling of municipal buses or other hydrogen-based vehicles, and supplementing intermittent renewable energy sources such as photovoltaics.

Known as the CO2/H2 Active Membrane Piston (CHAMP) reactor, the device operates at temperatures much lower than conventional steam reforming processes, consumes substantially less water and could also operate on other fuels such as methanol or bio-derived feedstock. It also captures and concentrates carbon dioxide emissions, a by-product that now lacks a secondary use -- though that could change in the future.

Unlike conventional engines that run at thousands of revolutions per minute, the reactor operates at only a few cycles per minute -- or more slowly -- depending on the reactor scale and required rate of hydrogen production. And there are no spark plugs because there's no fuel combusted.

"We already have a nationwide natural gas distribution infrastructure, so it's much better to produce hydrogen at the point of use rather than trying to distribute it," said Andrei Fedorov, a Georgia Institute of Technology professor who's been working on CHAMP since 2008. "Our technology could produce this fuel of choice wherever natural gas is available, which could resolve one of the major challenges with the hydrogen economy."

A paper published February 9 in the journal Industrial & Engineering Chemistry Research describes the operating model of the CHAMP process, including a critical step of internally adsorbing carbon dioxide, a byproduct of the methane reforming process, so it can be concentrated and expelled from the reactor for capture, storage or utilization. Other implementations of the system have been reported as thesis work by three Georgia Tech Ph.D. graduates since the project began in 2008. The research was supported by the National Science Foundation, the Department of Defense through NDSEG fellowships, and the U.S. Civilian Research & Development Foundation (CRDF Global).

Key to the reaction process is the variable volume provided by a piston rising and falling in a cylinder. As with a conventional engine, a valve controls the flow of gases into and out of the reactor as the piston moves up and down. The four-stroke system works like this:

• Natural gas (methane) and steam are drawn into the reaction cylinder through a valve as the piston inside is lowered. The valve closes once the piston reaches the bottom of the cylinder.
• The piston rises into the cylinder, compressing the steam and methane as the reactor is heated. Once it reaches approximately 400 degrees Celsius, catalytic reactions take place inside the reactor, forming hydrogen and carbon dioxide. The hydrogen exits through a selective membrane, and the pressurized carbon dioxide is adsorbed by the sorbent material, which is mixed with the catalyst.
• Once the hydrogen has exited the reactor and carbon dioxide is tied up in the sorbent, the piston is lowered, reducing the volume (and pressure) in the cylinder. The carbon dioxide is released from the sorbent into the cylinder.
• The piston is again moved up into the chamber and the valve opens, expelling the concentrated carbon dioxide and clearing the reactor for the start of a new cycle.
  "All of the pieces of the puzzle have come together," said Fedorov, a professor in Georgia Tech's George W. Woodruff School of Mechanical Engineering. "The challenges ahead are primarily economic in nature. Our next step would be to build a pilot-scale CHAMP reactor."

The project was begun to address some of the challenges to the use of hydrogen in fuel cells. Most hydrogen used today is produced in a high-temperature reforming process in which methane is combined with steam at about 900 degrees Celsius. The industrial-scale process requires as many as three water molecules for every molecule of hydrogen, and the resulting low density gas must be transported to where it will be used.

Fedorov's lab first carried out thermodynamic calculations suggesting that the four-stroke process could be modified to produce hydrogen in relatively small amounts where it would be used. The goals of the research were to create a modular reforming process that could operate at between 400 and 500 degrees Celsius, use just two molecules of water for every molecule of methane to produce four hydrogen molecules, be able to scale down to meet the specific needs, and capture the resulting carbon dioxide for potential utilization or sequestration.

"We wanted to completely rethink how we designed reactor systems," said Fedorov. "To gain the kind of efficiency we needed, we realized we'd need to dynamically change the volume of the reactor vessel. We looked at existing mechanical systems that could do this, and realized that this capability could be found in a system that has had more than a century of improvements: the internal combustion engine."

The CHAMP system could be scaled up or down to produce the hundreds of kilograms of hydrogen per day required for a typical automotive refueling station -- or a few kilograms for an individual vehicle or residential fuel cell, Fedorov said. The volume and piston speed in the CHAMP reactor can be adjusted to meet hydrogen demands while matching the requirements for the carbon dioxide sorbent regeneration and separation efficiency of the hydrogen membrane. In practical use, multiple reactors would likely be operated together to produce a continuous stream of hydrogen at a desired production level.

"We took the conventional chemical processing plant and created an analog using the magnificent machinery of the internal combustion engine," Fedorov said. "The reactor is scalable and modular, so you could have one module or a hundred of modules depending on how much hydrogen you needed. The processes for reforming fuel, purifying hydrogen and capturing carbon dioxide emission are all combined into one compact system."

                

Distance Relay Fundamentals

Distance functions have been in use for many years and have progressed from the original electromechanical types through analog types and now up to digital types of functions.

Simple MHO Function

A simple mho distance function, with a reach of Z ohms, is shown in Figure 1. This diagram is exactly equal to an R-X diagram except that all of the impedance vectors have been operated on by the current I. The mho function uses the current and voltage measured at the relay to determine if the apparent impedance plots within the mho characteristic.

If the angle is less than or equal to 90°, then the fault impedance Zf plots within the characteristic, and the function will produce an output.

If the angle is greater than 90°, then Zf falls outside of the characteristic and no output will be produced. Assume that the angle of maximum reach (q) and the angle of ZL (f) are equal. On that basis, the conditions shown in Figure 2 will be obtained. The key point to note in this phasor analysis (a convenient way to view relay performance) is the magnitude of the IZ – V (Vop) phasor and its relationship to the V (Vpol) phasor.

Operation will occur whenever Vop and Vpol phasors are within 90° of each other and provided both Vop and Vpol are greater than the minimum values established by the sensitivity of the relay design.

source:http://electrical-engineering-portal.com/

Energy-Free AC? Heat-Reflecting Wrap Could Cool Without Power!

A heat-reflecting, futuristic supermaterial that looks like a roll of plastic wrap could one day cool both houses and power plants without using any energy, according to a new study.

Unlike solar panels, the material keeps working even when the sun sets, with no additional electricity. And the plastic wrap is made up of cheap, simple-to-produce materials that could be easily mass-produced on rolls.

"We feel that this low-cost manufacturing process will be transformative for real-world applications," Xiaobo Yin, a mechanical engineer and materials scientist at the University of Colorado Boulder, said in a statement.

Radiative cooling

When radiation, such as sunlight, hits an object, different wavelengths of light can be reflected, transmitted or absorbed, depending on the properties of the material. For instance, black-colored materials, such as asphalt, tend to absorb most incoming visible light, while pale or shiny objects tend to reflect that light.

Yin said he and his colleagues wondered whether they could

manipulate the movement of light through a material so that the substance would efficiently cool objects passively, without using electricity. To do so, they looked to a giant: Earth, which on clear nights cools itself by radiating infrared light out into the cosmos. The catch is that Earth heats up tremendously during the day as incoming rays of sunlight bombard the planet.

However, the team suspected there was a way to harness radiative infrared cooling while simultaneously deflecting incoming rays from the sun, Yin said. 

The team devised a three-compound metamaterial whose base layer is a sheet, slightly thicker than aluminum foil, made of the see-through polymer polymethylpentene. The researchers then randomly interspersed miniscule glass beads throughout the material and coated the bottom with a thin layer of reflective silver. 

The glass beads were just the right size to induce a quantum effect known as phonon-polariton resonance. This effect occurs when a photon, or light particle, in the infrared spectrum interacts with vibrations in the atoms of the glass. The researchers found that when sunlight hit the top of the material, the glass beads and shiny silver bottom of the material scattered the visible light back out into the air. Meanwhile, infrared radiation passed from the bottom out through the top of the material, allowing whatever was beneath the material to cool off, the investigators said.  

In total, about 96 percent of the sunlight that hit the material bounced back off, the researchers reported on Feb. 9 in the journal Science.

Cool shade

When the researchers tested the material in the field, they found that it created a cooling effect equivalent to about 110 watts per square meter over a 72-hour period and up to 90 watts per square meter when facing direct sunlight at high noon, the scientists said in a statement. That's about the same amount of power as is produced by a typical solar panel in those time periods. (The material passively cools, but does not actively provide power like a solar panel does).

"Just 10 to 20 square meters [107 to 215 square feet] of this material on the rooftop could nicely cool down a single-family house in summer," study co-author Gang Tan, a civil and architectural engineering professor at the University of Wyoming, said in a statement.

The new material could also be used to cool off thermoelectric power plants, which currently use water and energy to keep machinery cool, the researchers said. In addition, the new material could increase the lifetimes and improve the operating efficiencies of solar panels, which often get too hot to work efficiently, the scientists said.

"Just by applying this material to the surface of a solar panel, we can cool the panel and recover an additional 1 to 2 percent of solar efficiency," Yin said. "That makes a big difference at scale."

Source- www.livescience.com

TYPES OF BOND

Types of Brick Bonds

1. English bond,
2. Flemish bond,3. Stretching bond,4. Heading bond,5. Garden wall bond,6. Facing bond,7. Raking bond,8. Dutch bond,9. English cross-bond,10. Zig-Zag bond,11. Silverlock’s bond.

3. Stretching bond:

In this arrangement of bonding, all the bricks are laid as stretchers. The overlap, which is usually of half brick, is obtained by commencing each alternate course with a half brick bat. Stretching bond is used for half brick wall only. This bond is also termed as running bond and is commonly adopted in the construction of half brick thick leaves of cavity walls, partition walls, etc. Since there are no headers, suitable reinforcement should be used for structural bond.

4. Heading bond :

In this type of bonding all the bricks are laid as headers on the faces. The overlap, which is usually-of half the width of the brick is obtained by introducing a three-quarter bat in each alternate course at quoins. This bond permits better alignment and  as such it is used for walls curved on plan. This bond is chiefly used for footings in foundations for better transverse distribution of load.

5.Garden wall bond:

This type of bond is suitably adopted for one brick thick wall which may act as a garden wall or a boundary wall. In garden wall bond, it is possible to build uniform faces for a wall without much labour or expense. This type of bond is not so strong as English bond and its use is restricted to the construction of dwarf walls or other similar types of walls which are not subjected to large stresses. On accounts of its good appearance, this bond is sometimes used for the construction of the outer leaves of cavity walls.

There are two types of garden wall bond,

(a) English garden wall bond
(b) Flemish garden wall bond

(a) English garden wall bond. The general arrangement of bricks in this type of bonding is similar to that of English bond except that the heading courses are only inserted at every fourth or sixth course. Usually the arrangement consists of one course of headers to three courses of stretchers. A queen closer is placed next to the quoin header of the heading course to give the necessary lap.

(b) Flemish garden wall bond. This consists of alternate course composed of one header to three or sometimes even five stretchers in series throughout the length of the courses. Each alternate course contains a three quarter bat placed next to the quoin header and a header is laid over the middle of each central stretcher.

6.Facing bond:

This arrangement of bricks is adopted for thick walls, where the facing and backing are desired to be constructed with bricks of different thickness. This bond consists of heading and stretching courses so arranged that one heading course comes after several stretching courses. Since the number of joints in the backing and the facing differ greatly, the load distribution is not uniform. This may sometimes lead to unequal settlement of the two thickness of the wall.

7.Raking bond:

This is a bond in brick work in which the bonding bricks are laid at any angle other than zero or ninety degrees. This arrangement helps to increase the longitudinal stability of thick walls built in English bond. In this arrangement of bonding, the space between the external stretchers of a wall is filled with bricks inclined to the face of the wall. This bond is introduced at certain intervals along the height of a wall.

There arc two common forms of raking bond ;
(a) Herring hone bond
(b) Diagonal bond.

(a) Herring-bone bond. This type of bond is best suited for very thick walls usually not less than four bricks thick. In this arrangement of brick work, bricks are laid in course inclined at 45° in two directions from the centre. This bond is also commonly used for brick pavings.

(b) Diagonal bond. This bond is best suited for walls which are 2 to 4 brick thick. This bond is usually introduced at every fifth or seventh course along the height of the wall. In this bond, the bricks arc placed end to end in such a way that extreme corners of the series remain in contact with the stretchers.

8.Dutch bond:

This bond is a modification of the old English cross bond and consists of alternate courses of headers and stretchers. In this arrangement of brick work, each stretching course starts at the quoin with a three-quarter bat and every alternate stretching course has a header placed next to the three-quarter brick bat provided at the quoin.

9.English cross-bond:

This is similar to English bond and consists of alternate course of headers and stretchers. However, in this bond, queen closer are introduced next to quoin headers and each alternate stretching course has header placed next to quoin stretcher. This bond is sufficiently strong and bears a good elevation.

10. Zig-Zag bond:

This is similar to herring-bone bond with the only difference that in this case the bricks are laid in a zig-zag fashion. This is commonly adopted in brick paved flooring.

11. Silverlock’s bond:

This is a form of bonding brick-work in which bricks are laid on edge. It is economical but weak in strength and hence it is only recommended for garden walls or partition walls. In this bond, the bricks are laid as headers and stretchers in alternate courses in such a way that headers are laid on bed aid the stretchers are laid on edge forming a continuous cavity.

Ground resistance using clamp meter, but be carefull!

The ground clamp meter / tester is an effective and time-saving tool when used correctly because the user does not have to disconnect the ground system to make a measurement or place probes in the ground.

The method is based on Ohm’s Law, where:

R (resistance) = V (voltage) / I (current)

The clamp includes a transmit coil, which applies the voltage and a receive coil, which measures the current. The instrument applies a known voltage to a complete circuit, measures the resulting current flow and calculates the resistance (see figure 1).

The clamp method requires a complete electrical circuit to measure. The operator has no probes and therefore cannot set up the desired test circuit. The operator must be certain that earth is included in the return loop. The clamp tester measures the complete resistance of the path (loop) that the signal is taking. All elements of the loop are measured in series.

The method assumes that only the resistance of the ground electrode under test contributes significantly. Based on the math behind the method (to be reviewed below), the more returns, the smaller the contribution of extraneous elements to the reading and, therefore, the greater the accuracy.

In addition, it includes the bonding and overall connection resistance. Good grounding must be complemented by “bonding”, having a continuous low-impedance path to ground. Fall of potential measures only the ground electrode, not the bonding (leads must be shifted to make a bonding test).

Because the clamp uses the grounding conductor as part of the return, an “open” or high resistance bond will show up in the reading.

The clamp ground tester also allows the operator to measure the leakage current flowing through the system. If an electrode has to be disconnected, the instrument will show whether current is flowing to indicate whether it is safe to proceed.

Unfortunately, the clamp ground tester is often misused in applications where it will not give an effective reading. The clamp method is effective only in situations where there are multiple grounds in parallel. It cannot be used on isolated grounds as there is no return path.

source:http://electrical-engineering-portal.com

Electrical design of the on-site generation system

Installation design of the generator

The electrical design and planning of the on–site generation system is critical for proper system operation and reliability.

This chapter covers installation design of the generator and related electrical systems, their interface with the facility, and topics regarding load and generator protection.

Typical Electrical System Designs

This section provides examples of typical electrical system designs used in low and medium/high voltage on–site power generation applications. It includes descriptions of different methods of generating at medium voltage such as the use of transformers in single and multiple generator configurations. While it is impossible to show every combination; the designs presented in this section are often used.

Several of the designs presented include paralleling capabilities and a brief discussion of the merits and risks associated with paralleling is provided.

Electrical System Designs tend to vary considerably based on the needs, or primary functions of the power generation equipment in the application. A system design that is optimized for emergency service situations will generally not be the best that it can be for interruptible service and is definitely not the same type of system design as might be seen in a prime power application.

Other differences are more subtle. Protection in a standby system is minimized in favor of greater reliability while in prime power we tend to move toward greater emphasis on protection of equipment. Coordination is often more of a concern in emergency applications. In standby applications grouping of loads might be commonly done based on location of loads within the facility, while in emergency applications, the grouping is based on priority of service.

source:http://electrical-engineering-portal.com