Low Voltage Effects on Ac Motors

Low Voltage Effects on AC Motors A drop in voltage will result in a proportionate increase in current. If the current exceeds the nameplate rating and is not corrected, this can result in damage to the motor from overheating Nameplate Rating An electric motor will have a nameplate rating for both voltage and amperage. When a load is on a motor, the motor must draw a fixed amount of power. The required power is about equal to volts times amps. Should the voltage fall below the nameplate rating, the amperage will increase. This can result in increased heat that will shorten the motor's life, according to Motorsanddrives. om. Torque The motor is subject to several kinds of torque. The starting or start-up torque is the amount present when the motor is stationary and power is applied. The pull-up torque is the minimum amount necessary for the motor during the starting sequence. Effects of Low Voltage on Torque A reduced amount of voltage will reduce the amount of torque. This can result in difficulty for start loads. A reduction of voltage to 80 percent would result in a torque value of only 64 percent. In light loads, a reduction in voltage may actually be preferable because it will result in increased efficiency.Even a small voltage unbalance will result in large current unbalance during the running of motor by a factor of 6 times. †¢ Negative phase sequence components will lead to heating of motor †¢ Negative phase sequence currents leads to reduction in motor output torque. †¢ Motor is forced to run at higher slip leading to increased rotor loss and reduced efficiency. †¢ Electricity boards should look in to this phenomenon seriously where irrigation pump sets suffer the voltage imbalance, even 1% loss of efficiency for the country like India would mean a great loss. HP irrigation pump sets with a quantity of 6 Lakh approximate, the loss of power would be 22MW and annual wastage of Rs. 47. 5 millions (At 3 Rs/unit, 4 Hrs of Pump working and 6 month’s season Keys to maximize the service life of industrial motors Why do motors fail? Certain components of motors degrade with time and operating stress. Electrical insulation weakens over time with exposure to voltage unbalance, over and under-voltage, voltage disturbances, and temperature. Contact between moving surfaces causes wear.Wear is affected by dirt, moisture, and corrosive fumes and is greatly accelerated when lubricant is misapplied, becomes overheated or contaminated, or is not replaced at regular intervals. When any components are degraded beyond the point of economical repair, the motor’s economic life is ended. For the smallest and least expensive motors, the motor is put out of service when a component such as a bearing fails. Depending upon type and replacement cost, larger motors—up to 20 or 50 horsepower (hp)—may be refurbished and get new bearings, but are usually scrapped after a winding burnout.Still larger and more expensive motors may be refurbished and rewound to extend life indefinitely. An economic analysis should always be completed prior to a motor’s failure to ensure that the appropriate repair/replace decision is made. Extend Motor Life with Improved Bearing Care Bearing failures are the root cause for the great majority of electric motor downtime, repair and replacement costs. Bearing and motor manufacturers are aware of the situation. Motor repair shops can attribute much of their business to bearing failures.And motor users see bearing failure as the fundamental cause of virtually every electric motor repair expense. Studies conducted by the Electrical Apparatus Service Association also demonstrate that bearing failures are by far the most common cause of motor failures. Knowing that shaft bearings are the Achilles’ heel of industrial electric motors is not a new idea in maintenance departments, but what is new is recognizing that something can be done to prevent most motor bea ring failures. Factors Affecting Bearing Life Electric motors actually present a relatively easy duty for shaft bearings.The motor rotor is lightweight, yet because of its large shaft diameter, the bearings are large. For example, the bearings supporting the 140 lb. Rotor for a typical 40 hp. 1800 rpm industrial motor are so large that they have an L-10 minimum design fatigue life of 3000 years, or 10 percent of the bearings are statistically expected to fail from fatigue after 3000 years of operation. Plant operating experience, however, strongly contradicts such optimistic estimates of motor bearing life. In actual industrial environments, bearing failure is rarely caused by fatigue; it is caused by less-than-ideal lubrication.Because of contaminated lubrication, bearings fail well before they serve their theoretical fatigue life. There are many reasons for less than-ideal bearing lubrication. Lubricants can leak out; chemical attacks or thermal conditions can decompose or break d own lubricants; lubricants can become contaminated with non-lubricants such as water, dust, or rust from the bearings themselves. These lubrication problems can be eliminated. Motor bearings can last virtually forever by simply providing an ideal contamination-free, well-lubricated bearing environment.Conventional wisdom teaches that such an ideal motor bearing environment can be provided by using a dry-running lip seal or using sealed (lubricated-for-life) bearings. Indeed, for many light-duty applications, such bearing protection techniques are often sufficient to allow bearings to last as long as the equipment itself. However, these bearing protection methods have not significantly reduced the rate of bearing failure in severe-duty industrial motors. Bearings in industrial applications continue to fail because of inadequate lubrication caused by lubricant loss, contamination, and decomposition and break-down.Lip seals invariably wear out well before the bearing fails, and sealed bearings inherently foreshorten the life of a bearing to the service life of the contained grease (usually only about 3,000 to 5,000 hours for most industrial services). Maintenance professionals may find the following suggestions on how to forestall motor hearing failure obvious, but some new techniques and technologies are available. Lubricate Bearing at Correct Intervals Despite years of warnings from bearing manufacturers, over lubrication continues to plague many motor bearings. Too much grease can cause overheating of the bearings.The lubrication instructions supplied by the motor manufacturer will specify the quantity and frequency of lubrication. Generally, two-pole motors should be greased twice a year, four-pole and slower motors only once a year. Use the Best Available Grease The most commonly used bearing grease is polyurea-based, a low-cost, low-performance, highly compatible lubricant. However, it does not handle water well, a serious drawback for many industrial appli cations. It reacts readily with water and loses its ability to lubricate bearings. Industrial motor bearings should be lubricated with a synthetic-based aluminum complex grease.A high-quality grease pays for its additional cost in reduced motor downtime and repair costs. Keep Out Moisture Unless the motor is being hosed down or it operates in a humid environment, reasonably shielded motor bearings may not become seriously contaminated with moisture while the motor is running. However, when the rotor is shut down, moisture and condensation can collect on the surface of the bearing components. Eventually, this water breaks through the oil and grease barrier, contacts the metal parts of the bearing, and produces tiny particles of iron oxide.These rust particles make an excellent grinding compound when mixed with the grease. resulting in premature failure of the bearing because of surface degradation. Preventing water contamination is a major challenge to bearing housing design. Close s haft-to-endbell clearances cannot stop the movement of humid air. Contact seals will quit contacting, resulting in large gaps that allow movement of air and water vapor across the bearing. Vapor-blocking bearing isolators, such as the one illustrated, are among the more successful devices presently available to prevent water vapor from entering a stationary bearing.When the motor shaft is rotating, the isolator opens, eliminating the possibility of friction and wear. However, when the shaft is stationary, the isolator closes, preventing movement of air or water across its face. With no wear from rotating friction, the seal may last indefinitely, and surely as long as the fatigue-failure life of the bearing. Keep Out Dirt Lip seals, contact seals, and frequent grease replacement help minimize the amount of dirt and other air-borne abrasives that can contaminate bearing lubricant. These solutions, however, have some drawbacks.Lip seals have a short service life, and frequent grease di splacement is expensive and messy. One successful approach to keeping air-borne dirt and liquids out of an operating bearing is to install a labyrinth-type non-contact seal over the bearing housing. These bearing isolators, readily available from suppliers, combine a tortuous labyrinth path with impingement and centrifugal forces to trap and remove air-borne dirt and liquid; virtually no contamination can reach the bearing. Because the bearing isolator is a non-contact device, it will generally be the longest-lasting component of the motor.Although not intended as such, a bearing isolator could serve as an emergency sleeve bearing if the primary bearing fails, possibly preventing damage to the motor’s stator and rotor. In emergency situations, the bearing isolator can allow continued operation for a short time and still prevent the need to rewind the motor when the bearing is replaced. Bearing isolators constructed of bronze or other non-sparking materials also can prevent ha zardous sparks that could otherwise occur when the bearing’s rolling elements fail. Other SuggestionsImproved bearing protection and lubrication will reduce downtime and the maintenance costs of electric motors, but other important motor design features contribute to long service life, including over-sized high quality bearings, high-tech winding insulation, superior fan design, high-performance paint (such as epoxy) and a strong, rigid cast iron frame. These features, usually standard or readily available, are found in most industrial-grade severe-duty electric motors. High-performance bearing protection systems. however, are not universally accepted as essential for long motor life.Specifying permanent bearing protection for new motors, or retrofitting isolators onto existing equipment, usually requires initiative on the part of the user’s maintenance or engineering staff. Permanent, absolute bearing protection has a greater effect on motor life than any other decisi ons made in specifying, equipping, and caring for electric motors. Keeping bearings lubricated with the right amount of clean, uncontaminated, high-quality lubricant allows bearings in most industrial motors to outlast all other motor components.

Mudule guide

By the end of this module, successful students will typically be able to; demonstrate the ability to critically analyse and evaluate the reality of complex IHRM and employment relations issues from a variety of perspectives; demonstrate the ability to relate theory to practice; demonstrate the ability to evaluate the relative strengths and weaknesses of selected national HRI employment relations systems; demonstrate the ability to undertake ystematic management research as required by module assessments and in- module participation, synthesise information and reference appropriately; communicate effectively verbally and in writing; demonstrate the ability to use initiative and independence in study and application. 3 Format of Delivery There is one lecture (1 hour) and one seminar (1 hour) per week. 4 How StudyNet will be used to support this module StudyNet will be used for providing lecture notes and other materials relating to each session. These will be accessible prior to each l ecture. StudyNet will be used for all ommunication on the module. Additional reading and links to Journal articles will be put in the ‘Additional Reading folder under ‘Teaching Resources'. You should consult this folder on a regular basis as the readin supports your module.Teaching methods used on this module The module will use a variety of teaching methods which include lectures, seminars and workshops. A feature of the module is the emphasis placed upon student presented seminars. Students are expected to participate fully in the module. Prior to each session, they are expected to familiarise themselves with the lecture topic by rawing upon the detailed guided reading and to read selectively from the seminar reading list. In addition, they are encouraged to keep abreast of current events and be prepared to discuss these and their own work experiences (where appropriate) in the seminar groups. This variety of methods will enable students to effectively achieve the modu le learning outcomes.Students are expected to attend this module regularly as an essential part of their learning lies not only in the lecture but also in the contribution that students make to the seminar programme. If students are unable to attend, they must advise the tutors. a Module schedule and lecture/seminar information In this section you will find a week by week schedule for this module. There is one lecture (1 hour) and one seminar (1 hour) per week. Please note that there are sometimes unforeseen circumstances, such as staff illness, that may necessitate communicate these changes to you in good time. The table below provides a summary of the teaching programme. You need to consult the full schedule for the directed reading.

Krispy kreme doughnuts, inc. Essay

This case considers the sudden and very large drop in the market value of equity for Krispy Kreme Doughnuts, Inc., associated with a series of announcements made in 2004. Those announcements caused investors to revise their expectations about the future growth of Krispy Kreme, which had been one of the most rapidly growing American corporations in the new millennium. Your task is to evaluate the implications of those announcements and to assess the financial health of the company. This case provides an early exercise in financial statement analysis and lays the foundation for two important financial themes: the concept of financial health, and the financial-economic definition of value and its determinants. Suggested Questions for Advance Assignment 1.What are the definition and purpose of an income statement, as shown in case Exhibit 1? What are the definition and purpose of a balance sheet as shown in case Exhibit 2? How are the two statements related? In answering the questions above, highlight some of the following accounting choices and sources of variation in reported results in (i) Cash and cash equivalents, (ii) Accounts receivables, (iii) Inventories, (iv) Property, plant, and equipment, (v) Goodwill and other intangibles, (vi) Revenues, and (vii) Expenses 2.Are Krispy Kreme’s financial statements exact? Does management have any discretion over how those accounts are estimated? 3.What can the historical income statements (case Exhibit 1) and balance sheets (case Exhibit 2) tell you about the financial health and current condition of Krispy Kreme Doughnuts, Inc.? Clues: Discuss Krispy Kreme’s growth; DuPont Analysis; liquidity, leverage, and profitability; and peer comparisons (Refer case Exhibits 7, 8 and 9) 4.How can financial ratios extend your understanding of financial statements? 5.Is Krispy Kreme financially healthy at year-end 2004? Given your assessment of Krispy Kreme’s health, why did its stock price drop by 80% between 2003 and 2004? 6.What is the source of intrinsic investment value in this company? Does this source appear on the financial statements? 7.Review the events since the date of the case. See the company’s Web site for updates on its financial information (http://www.krispykreme.com).

English Language Content Standards Essay Example | Topics and Well Written Essays - 500 words

English Language Content Standards - Essay Example They will also address how to give a full curriculum, and has focus of areas of students that may need extra help to reach the standards. These standards are part of an essential discipline because it has become essential to communicate fluently in English. Language tools are needed to be able to openly communicate with other people, as well as to express you won ideas and though processes. The standards will help students learn the tempo and structure of language in their early years, until they are able to master vocabulary, expression, and the ability to gather evidence to support an idea. Studies show that children who fall behind in reading have a small chance of catching up, so it is crucial to help engrain these ideas and skills as early as possible inside of the education system. Also, though literature students are able to learn just as much about history as they would about the time period of the writing, and this benefits them in both ways. Students should be able to read a vast source of materials that benefit not only their English training, but also their history, math, social science, science, and gover nment classes as well. Students must able read a vast range of texts in order to help them gain the understanding of them, and to also try out best to instill into them a love for reading, so that they may one day gain pleasure in this simple

Discovery, Appearance and Meaning of Cave paintings in France and Essay

Discovery, Appearance and Meaning of Cave paintings in France and Spain - Essay Example The essay "Discovery, Appearance and Meaning of Cave paintings in France and Spain" explores Cave paintings in France and Spain. Nearly two hundred cave paintings have been discovered so far in France and Spain, and they still continue, as the recent discovery of cave paintings in the Vilhonneur forests, in the Charente region of western France suggest. However, the cave paintings in the Lascaux Cave of Montignac, in the Dordogne region of southwest France, and Altamira, in northwest Spain, still remain the more significant examples of pre-historic cave paintings. The initial discovery of the caves, and the paintings at Altamira were made in the later half of the nineteenth century by accident. In 1868 a hunter’s dog chasing a fox fell among some boulders, and the hunter, in attempting to rescue the dog discovered the entrance to the famous cave. The cave paintings took more than a decade later to be discovered, again by accident. The owner of the estate in which the cave was located was an amateur archeologist. His young daughter accompanied him on one of his trips into the cave, to look for tools, in 1879. She looked up at the ceiling, and became the first person in modern times to espy the herd of red animals painted across the ceiling. Initially these paintings were not accepted as pre-historic paintings, and believed to be forgeries a mere twenty years old. In the beginning of the twentieth century efforts of the French priest Henri Breuil made the world aware of this finest example.

Right Thumb Pain Child Treatment Case Study Example | Topics and Well Written Essays - 2500 words

Right Thumb Pain Child Treatment - Case Study Example Attending day care with other children. At home, he is left under the care of a house-help who is employed to take care of an ailing grandparent living with the family.Playful and loves pets, has two pet cats at home. He likes playing with other children and sometimes takes his two pets with him to play.O/E: The child is in pain, with an open wound on the dorsal side of the right thumb. The bite is 2 cm long and canine marks are also visible on the frontal side of the thumb. The hand is inflamed from the carpal tunnel distally. The patient however guards the whole hand and does not agree to be touched. Only the mother can touch.HEAD AND NECK: No abnormality detected.Hands: Both hands are strong, with normal range of motion and symmetry. The right hand is inflamed from wrist joint downwards and the patient guards the entire hand and reports pain.No other abnormal observation on assessment.Right Wrist and thumb: NADRt. Thumb: superficial wound on anterior aspect of proximal phalanx abo ut 0.5cm in diameter. 1cm in depth (Dealey 2005, p.57).No bleeding noted, slight swelling around the bite wound, no erythema, no atrophy, no sign of infection, no bruising.ROM: Active: Flexion- full range; with minimal pain on anterior aspect of distal phalanx Extension- full range; pain free movementAdduction- full range; with minimal pain on anterior aspect of distal phalanxMedial Rotation- full range; with minimal pain on anterior aspect of distal phalanx

Finance and Management Personal Statement Example | Topics and Well Written Essays - 1000 words

Finance and Management - Personal Statement Example Throughout my life I have always been a very hard worker. I am a professional athlete currently working as a UFC fighter. My career requires a lot dedication and self discipline. These attributes can help me in my studies because being a student also requires a lot of sacrifice and self control. Universities such as the City University London are offering its students a learning experience bringing into the classroom the latest technologies to enhance the learning atmosphere. As an aspiring business student I realize that in order to succeed at graduate school I will have to dedicate myself more than ever. I already have an educational background in business. I studied my undergraduate degree at Ezerbaijan State Economic University graduating with a major in finance and credit. My prior exposure to business school will facilitate my transition better than other candidates that studied other fields. During the last of couple of years I have gained valuable experience in the business w orld working as a business development manager for a courier company. Working for this company was one of the factors that inspired me to study graduate school. In this job I learned a lot, but I realized that my skill sets and capabilities in business were not sufficient for me to continue a path towards ascension in the business world. I like being a manager a lot. ... The starting salary of a person with a master’s degree is about 20% higher than people with a bachelor’s degree. It is estimated that a person with a masters degree will earn over ?1.63 million over a lifetime. Continuing my education in business is very important for me. I like the fact that a masters’ degree opens up opportunities and increases your income capacity, but the real reason I want to attend City University London is to expand my business knowledge. I want to apply that knowledge at work in order to improve my performance. I also have aspirations beyond working for the private sector. One of my goals in life is to open up my own business. The business world has changed a lot since the start of the 21st century. Globalization has become more influential and technologies such as broadband internet have expanded the reach of ecommerce. Foreign markets such as the US marketplace have a growing customer base of online customers with ecommerce sales reachi ng ?93 billion in 2010. Due to the changing dynamics of business I have to be able to keep up with changes. The only way that I will be prepared for running my own business in today’s marketplace is by first completing a master’s degree in finance and management. One of my hobbies is reading books. When a person reads a lot they gain endurance at reading. This skill will help me lot in this new stage of my life. Graduate students often have to read hundreds of pages in textbooks, cases, and journals on a weekly basis. For me reading and learning about business is going to be a very gratifying experience. Some of the topics in business that I need to improve to become better at my career are international finance, foreign exchange markets, diplomacy, and negotiations. For me