The No Load Circuit And Short Circuit Characteristics Biology Essay

The No Load Circuit And Short Circuit Characteristics Biology Essay The Ward-Leonard system is a conventional speed control method. It consists of a 3 phase induction machine controlling a separately excited DC generator. The DC generator in turn supplies a variable DC voltage to a DC motor. It is basically a DC variable speed drive [2]. The Ward-Leonard system is shown below in Figure 1. Figure : Ward-Leonard system setup The principle behind the Ward-Leonard system is that the DC generator can actually influence the motor to develop a torque and speed required by the load [3]. Thus the speed of the generator is directly proportional to the armature voltage applied to the DC motor [2]. The output voltage of the DC generator is controlled by adjusting the exciting voltage (field voltage), this then controls the speed of the DC motor [2]. Applications Travelling cranes Lifts Mine hoists Boring machines Table : Ward-Leonard system advantages and disadvantages Advantages Disadvantages Very wide range of speeds High cost Provides step less speed control Low over-all efficiency Experiment Apparatus 2- coupled induction machine and dc motor (as shown below in Figure 2) 4- digital multimeters (DMM) 2- Variac (Excitation field) Tachometer Figure : Coupled induction machine and dc machine Objectives of the experiment Characterise the DC machines and determine the equivalent circuits. Derive the power flow equations between the DC machines in terms of the equivalent circuits. Control the power flow between the DC machines by adjusting the field currents. Then compare the measured results with the expected theoretical power flow. Experiment procedure and setup No-load Test This test was used to determine the armature voltage. Before the experiment began the armature and field resistance were both measured. The Variac (exciter) was then connected to the field port on the DC machine. The Digital multimeter was connected to the armature port on the DC machine in order to measure the armature voltage. The DC machine was coupled to a three phase induction machine which was first turned on to run the DC machine. The setup is shown below in Figure 3. Using the knob on the Variac, increase the field voltage with an increment of 10V ( also increases) and for each case determine the armature voltage. This was done from 0V to the rated field voltage 110V. Now decrease the field voltage to demagnetise the DC machine from 110V to 0V also with an increment of 10V. Note the residual magnetism. Figure : No-Load test setup Short-Circuit Test This test was used to determine the armature current. The same procedure for the No-Load test was followed but in this case the digital multimeter was connected in series in the armature port in order to measure the current. Using the knob on the Variac, increase the field voltage with an increment of 10V and for each case determine the armature current. This was done from 0V to the rated field voltage 110V. The DC machine was demagnetised from 110V to 0V also with an increment of 10V recording the armature current. Ward Leonard experiment This setup was used to determine the power flow between the machines. The two coupled machines were connected together as shown below in Figure 4. A coupled machine is shown in Figure 1. The coupled machines were connected together through the armature. The positive terminals of the armature were connected together and the negative terminals were connected together. A digital multimeter was connected in between the positive terminals of the armature in order to measure the current. Each DC machine was connected to Variac through the field port. Both the Variac machines were turned down to 0V. The two induction machines were switched on both at the same time from the 3 power supply. The Variac knobs were both turned at the same time with an increment of 10V from 0V. This is done up until the multimeter reads 0A. The 0A was obtained at a field voltage of 110V. At this stage the second machine was left constant and the field voltage of the first machine was turned down at an increment of 10V, whilst recording the current and the speed of the machine without exceed the speed of 1502 rpm. A tachometer was used to measure the speed. After that the first machine was calibrated back to 110V, were the multimeter reads 0A. Now the first machine was left constant and the field voltage of the second machine was turned down at an increment of 10V, whilst recording the current and the speed of the machine without exceed the speed of 1502 rpm. A tachometer was used to measure the speed. After this then the practical is complete, the next step is to deduce an equation for the power as a function of excitation (field current) based on the machine characteristics. Then plot the graphs. Figure : Power flow setupC:UsersMashDesktopf.bmp Safety Do not exceed the ratings of the machines and all the other equipment. Switch off the equipment after completing the practical. Results Characterisation of DC machine Table : Armature and field resistance Resistance Before After 7.3 à ¢Ã¢â‚¬Å¾Ã‚ ¦ 9.8 à ¢Ã¢â‚¬Å¾Ã‚ ¦ 573 à ¢Ã¢â‚¬Å¾Ã‚ ¦ 542 à ¢Ã¢â‚¬Å¾Ã‚ ¦ No-load characteristics G:Machine Pracopennn.bmp Figure : No-load circuit Table : No-load test results Magnetizing Demagnetizing Field volts (V) Armature volts (V) Field volts (V) Armature volts (V) 0 0 1.6 9 10 27.8 10 35 20.8 61.1 20.5 68 30 88.9 30.1 97 40 116.8 38.2 119 50.1 141.1 50.1 148 60.6 165.1 60.1 170 70 181.9 69.5 185 80 196.2 80.4 200 90 209 90.5 211 100.2 218 100.9 220 110.3 227 110.3 227 Figure : No load test results plot The following table shows the calculated field current using the measured field resistance of 573 à ¢Ã¢â‚¬Å¾Ã‚ ¦. Table : Amperes in the field coils Magnetizing Demagnetizing Field volts (V) Field Amperes (A) Field volts (V) Field Amperes (A) 0 0.0000 1.6 0.0028 10 0.0175 10 0.0175 20.8 0.0363 20.5 0.0358 30 0.0524 30.1 0.0525 40 0.0698 38.2 0.0667 50.1 0.0874 50.1 0.0874 60.6 0.1058 60.1 0.1049 70 0.1222 69.5 0.1213 80 0.1396 80.4 0.1403 90 0.1571 90.5 0.1579 100.2 0.1749 100.9 0.1761 110.3 0.1925 110.3 0.1925 Figure : DC generator no-load characteristics Comments The graph shows the relationship between the no-load armature voltage and the field current at a constant speed of 1496 rpm. The magnetization curve is a straight line up to a field current of 0.1A, after this point the graph approaches a condition known as saturation, thus any increase in the field current does not result in an increase in the armature voltage. Consequently the demagnetizing plot is above the magnetizing plot, this is due to the residual magnetism and hence the curve begins just above the 0 mark (a little way up). Closed circuit test G:Machine Pracshortt.bmp Figure : Closed circuit diagram Table : Closed circuit results Magnetizing Demagnetizing Field volts (V) Armature current (A) Field volts (V) Armature current (A) 1.7 2.54 1.6 0.21 10.8 3.63 10.7 1.1 20.5 4.52 18.8 1.81 30.8 4.72 29.5 2.64 40 5.54 39.9 3.37 50.9 6.4 50.2 3.93 60.7 5.59 60.8 4.44 70 6.01 70.7 5.05 80 6.1 80.8 5.5 90 6.52 90 5.9 100 6.92 100 6.54 111 7.4 111 7.4 Figure : Short-circuit characteristics Nameplate Information No-load circuit calculations Figure : No-load Fitted-curve This can be written as Using Figure 10 we can use the fitted plot of the no-load saturation curve above to determine the constant. The measured speed is used. From Thus we can calculate: But in practice we can approximate the value of the torque constant Short-circuit calculations Figure : Short circuit fitted plot This can be written as As calculated above Thus by substitution Thus now we can determine the armature resistance Coupled machines (Ward-Leonard system) ) 110.1 110 0.1 1492 1491 0.205224 0.15597 110.1 100 0.15 1492 1492 0.186567 0.212687 110.1 90 0.49 1490 1494 0.16791 0.625299 110 79.9 0.86 1486 1499 0.149067 0.974303 110.1 70 1.22 1490 1498 0.130597 1.210896 110 60 1.59 1480 1499 0.11194 1.352687 110.1 50 2.03 1484 1501 0.093284 1.439179 110.1 40.3 2.45 1484 1503 0.075187 1.399974 Power flow ) 110 110 0.1 1492 1492 0.205224 0.15597 100 110 -0.83 1492 1496 0.186567 -1.17687 90 110 -1.17 1480 1500 0.16791 -1.49306 80 110 -1.56 1470 1500 0.149254 -1.76955 70 110 -2.05 1474 1500 0.130597 -2.0347 60.1 110 -2.25 1483 1502 0.112127 -1.91737 Derivation of power equation Figure : Ward-Leonard system setup Figure : Ward-Leonard system equivalent circuit Now from Figure above we expect that Where (For the generator) (For the motor) (For the generator) (For the motor) Equate equation (1) and (2) Rewrite the equation Now we observe that Let This equation remains the same, it just depends which machine is a generator and which machine is a motor. As mentioned above to determine which machine acts as a generator or motor, we look at the following sign conversion. Conclusion DC machine Characterisation The DC machine characterisation of the generator was successfully done, both the no-load test and the short circuit test were done and all the parameters were calculated. The parameter calculated include the armature resistance which was found to be 6.25 à ¢Ã¢â‚¬Å¾Ã‚ ¦ as compared to the measured and the rated armature resistance it is within range ( difference). The characterisation also helps us understand how the dc works; by using the saturation curves we can determine the point where the machine starts saturation and determine the critical resistance. We can also determine information about the machine which would normally be given in the nameplate. Ward-Leonard system and the power flow The power flow equation was successfully derived and found as the equation below The equation was derived from the Ward-Leonard system that was setup in the practical. The practical showed that the power can be controlled between two DC machines using this setup. In the practical the power flowed from the generator to the motor, this was seen through the current having a negative current flowing in one direction and a positive current flowing to the other direction. The practical was successful and it clearly corresponds to the theory. What I leaned The practical was useful in terms of helping us understand the concept of residual magnetism which is the same as in the theory. The practical was also a good representation in terms of how an elevator/lift works.

Girls Development During Adolescence: Diminishment of Self Essay

Large numbers of American girls face a crisis during adolescence. Numerous studies document the disturbing trends that affect girls during this vulnerable time. Girls' IQ scores drop. Their grades in math and science decline dramatically. The confidence, curiosity, and willingness to take risks that mark their childhood years are replaced by unassertiveness, boredom, and a cleaving to the status quo. Girls at this age become prone to eating disorders, self-mutilation, and depression. Even girls without obvious signs of distress undergo a curious diminishing, as if all the interests and energies of their childhood must now be channelled into maintaining a narrow and alien definition of self. What happens to girls as they grow up? What causes this diminishment of self? What transforms them from the happy, confident people they are in childhood to the self-critical, sullen, and frightened adolescents they become? Psychologist Mary Pipher, author of Reviving Ophelia: Saving the Selves of Adolescent Girls talks about the "isms" that meet girls at the threshhold of adolescence--sexism, capitalism, and lookism. Who girls can be is no longer a wide-open playing field. They find themselves judged by how well they conform to a specific gender role. An enormous source of information about what it means to be female is the popular media. Music and music videos, movies, television, magazines, and commercials, many of them aimed at teenagers, all carry a loaded message--to be successful as a woman means adhering to a highly stylized script that defines for girls what womanhood is. Modern girls encounter an incredible contradiction in the messages they receive at this vulnerable time in their lives. On the one hand they ar... ...lem. We are buying into the mentality that fuels those images. Each of us must have the courage to examine our own unconscious pact with the scripts society hands us. We need to recognize the ways our power has been co-opted by the rewards we reap through compliance with the status quo. In what ways does our own diminishment hold us back? Can we move beyond that diminishment and reclaim our right to be whole? Can we step outside the gender boundaries we have internalized into a place where we finally exist as humans, first, and men and women second? It is through claiming our own integrity that we give girls permission to expand beyond the status quo. It is our choice. When enough of us have moved beyond the cultural icons that define for us what masculinity and femininity are, those icons will fall away. There won't be an audience left to sustain them.

Eating Too Much Meat Will Kill You Essay

Bill Cosby once stated, â€Å"Did you ever see the customers in health-food stores? They are pale, skinny people who look half dead. In a steak house, you see robust, ruddy people. They’re dying, of course, but they look terrific.† On average, Americans consume about 8 oz. of meat a day, twice the amount as the rest of the world; about one-sixth of the total meat consumed, U.S being less than one-twentieth of the population. Meat is generally delicious, contains rich sources of proteins and minerals. Some nutritional diet programs like the Atkins Diet have linked certain types of meat-based diets to weight loss. On the contrary, eating too much meat has been linked to certain type of cancers, high cholesterol and an increased risk of contracting a foodborne illness. Americans need to recognize that diets high in meat increases the cancer risk and other health issues. Evidence suggested that consuming meat could damage the body. In a country known for its love for hambur gers and steak, consumers need to cut down on their meat for a healthy life. Consumers also need to understand grilling meat increase the risk of cancer. Part of the solution is eating healthy, but consumers also should be aware of what they’re eating. The big issue in America is quantity. Eating meat and fast-food meat on a daily basis for seven days a week, 365 days a year, is a big reason why the risk for cancer and other health diseases is dangerously high in U.S. United States slaughters more than 10 billion land animals every year (Freston 802), and the market research firm Packed Facts stated Americans spends 142 billion dollar on beef, chicken, pork, lamb at market retails. Eating too much red meat has been linked to increased risk of death from cancer and heart disease, according to a study from American Cancer Society, the more red meat you eat will increase the risk for cancer. A Journal published by the American Medical Association reported a 20-year study of nearly 149,000 adults between the ages of 50 and 74. Researchers examine the risk according to how much red meat, poultry, or fish the people had eaten. Researchers looked at how many people develop colon cancer after the study. The results were 30% to 40% are more likely to develop cancer in the lower part of the colon. People who ate the most processed meats were 50% more likely to develop colon cancer (Parish 6). Eating just three ounces meat a day increases the consumer’s chance of dying by 13 percent, and 20 percent increase if eating processed meat, like bacon and hot dogs. But it doesn’t mean we should completely cut out meat in our diet; these statistics demonstrates that the less meat you eat, the better. Consuming meat damages the body. According to Dr. Oz, from the Dr. Oz Show, eating a steak dinner can take two to three days to get out of your intestines (par. 3). Red meat takes more than 24 hours to completely digest. In the mean time, it is in your intestine rotting at 98 degrees, sending toxins through the body. Eating any food that does not completely digest will ruin your health. What happens is that the human stomach acids are not made to break meat down efficiently because of its high fat and protein contents. The body lacks the enzymes that digest proteins in the stomach. Protein digestion mainly takes place in the first section of the small intestines where the pancreas secretes the types of digestive enzymes to help break down nutrients into energy and allow the nutrients molecules enter the bloodstream. Hence, meat takes longer as it has to pass into the stomach and the intestines, opposed to carbohydrates, which are broken down easily by saliva and the stomach. Although red meat is digestible than any other food sources such as rice and vegetable, it remains in the digestive system for a longer period of time, leaving the meat to rot in your intestines. Dr Klein believes that animal protein is the primary cause for the inflammation of the intestines because meat rots in your stomach (4). It explains why eating animal protein for a long period of time can increase the risk of colon cancer. Also the kidneys work to remove excess protein from your body. Eating too much protein can stress out the kidney, leading to kidney damage. Grilling meat is a method that most people are familiar with. Grilling is part of American culture; it brings family and friends together for the holidays like Independence Day. Grilling is a method of cooking food hot and fast on your grill. Burgers, poultry, beef, seafood are typically grilled. Grilling is actually a much healthier option than frying food because it is low fat and you can grill food without adding oil on them. But unfortunately, grilling food may potentially introduce the risk for cancer. Those juicy hamburgers, especially the charred ones contains cancer causing chemical called carcinogen. When you grill meat, some of the fat drips down to the charcoal or flame and the smoke carry the carcinogen known heterocyclic amines (HCA ) and polycyclic armomatic hydrocarbons (PAH) to form. These compounds have been shown to affect our DNA and might cause cancer. PAH is the same smoke from forest fires, coal burning, car exhaust and smoking. Exposure to high amounts of PAH is dangerous to your health and long term exposure increase the risk of cancer. According to 2007 study in Epidemiology, women with high intakes of grilled, barbecued or smoked meats over their lifetime had a 74 percent chance of developing breast cancer (373). It is also important to not that these women has low intake of fruits and vegetables. Most people are not aware of the carcinogen when they are grilling the meat. But let’s face it, grilled meat taste good and people should not give up on their grass fed steak or burgers from the grill. There are couple ways to grill safely and reducing carcinogen. 1. Marinating meats for at least several hours that contains herb and spices can dramatically reduce HCA. Herbs/spices is highly potent antioxidant that helps prevent HCA formation. 2. Pre-cook the meat in either the oven or microwave and finish it on the grill to decrease the amount of the carcinogen. 3. Pick leaner cuts like skinless chicken, lean beef or pork; it decreases the fat from dripping down on the open flame. It also important to remember that well-done meat has a higher concentration of carcinogen. Medium-rare, or medium cook is healthier choice than well done. These tips to reduce and prevent carcinogen is a safe way to consume grilled meat, but what about restaurants that serves grilled meats? Unfortunately, the meat holds carcinogens. Study shows restaurant meat such as burgers, ribs, and chicken carry substantial amounts of carcinogen. Few years ago, KFC calls their new Grilled Chicken â€Å"the better-for-you chicken for health- conscious customers.† But a PCRM a test shows the grilled chicken contains a high level of carcinogen (Sullivan 12). Consumers eating grilled chicken from popular restaurant chains are exposed to substantial level of carcinogen. A study published in Nutrition and Cancers show that an independent laboratory examined one hundred samples from seven popular restaurants, and Phip, a carcinogen, was found in all the samples (33). These findings clearly show that eating grill chicken can potentially cause cancer. Consumers deserve to know what they’re eating is just as worse as a greasy high-fat fried chicken. It misleads consumers to think grilled chicken is healthy diet but in actuality a grilled chicken salad can increase the risk of breast cancer, prostate cancer, and other dangerous health disease. If that the case, shouldn’t the government or chain restaurant provide warning labels on their product? Since Tobacco Company labels their pack with a warning that cigarette causes cancer; restauran ts serving cancer-causing meat should do the same. When parents cook chicken for their children, they try to be health conscious. If people knew there were high levels of carcinogens in their grilled chicken, they may not choose it as a healthy alternative. Meat is part of American culture; Western men often forge a strong link between eating meat and masculinity. Eating too much meat is a common problem in American Society. I believe most Americans don’t realize that they’re eating too much meat. When comparing the size of the burger we’re eating today to the past decades, our burger has gotten bigger. Bacon is a big part of American culture today. It brings child-hood memories of how mothers cooked bacon for their children. It is also a common breakfast food and is often associated with family gatherings. But, eating bacon every single day of your life has life threatening repercussion to your health. Most processed meat like bacon or hot dogs contains sodium nitrate. Sodium nitrate is a food additive used in m any processed meats. It increases shelf life, gives any meat a fresh appearance, improves the smoky flavors of bacon, and slows the rate of the foul smell, and reduces bacteria (Kortboyer 5). It seems sodium nitrate is a great additive but it is widely regarded as a toxic ingredient. It is a highly carcinogenic chemical and once it enters the human digestive system; it release toxin to a number of internal organs including liver and pancreas. USDA tried to ban sodium nitrate in the 1970’s but was vetoed by food manufacturers who complained that they are trying to ban bacon from America and insisted the additive was safe. The sodium nitrate is found in almost every meat package. It’s listed right on processed meat products like bacon, turkey, hot dogs, and meats in canned soups. If it’s so dangerous, why does food manufactures use it? It sells more meat products because it makes the meat appear fresh and vibrant. Consumers are often influenced by the appearance of the meat, and sadly they will buy meat that looks fresh because of the additives, but in reality, the meat could be months old. A proven strategy to help combat sodium nitrates is to consume large doses of vitamin C and E before your meal. Another safe alternative is purchasing nitrite-free meat to reduce the exposure to sodium nitrate. But, meat without nitrates is prone to spoilage. I believe meat industry uses the saturated fat argument to distract consumers from real issues like cancer. Fruits with high saturated fat like coconut juice wont increase a person risk of cancer to jump up 50%. The real issue is what’s added to the meat during processing and packaging. While eating too much meat can be dangerous, the solution is to consume less. Meat is rich in protein and the body needs protein to maintain cellular tissue. Reducing meat intake benefits the bones. According to Dr. Campbell of Cornell University, animal sourced proteins extract more calcium from the bones, causing the bone to weaken (par. 4). Another good benefit of cutting back on meat is it that makes the consumer eat more nutritious foods. A study from American Journal of Clinical Nutrition reported that participants who were served a meal with less meat ate more vegetables (Rolls 916). Eating small portions of good quality meat can help curb meat cravings and will not jeopardize the health. Many health education websites like Meatless Mondays offer idea of cutting back on meat consumptions. Another healthy alternative is replacing meat with non-meat sources of protein. Small red beans, black beans, legumes, dairy products are all good source of protein. While fish and seafood are technically meats, they do not carry the same risks as red meat, chicken, and pork because they contain low saturated fat and cholesterol. Non-meat protein not only has low saturated fat and cholesterol, they contain healthy fats, vitamins and minerals the body needs. Besides, the average person only needs about eight grams of protein per 20 lbs of body weight. Make no mistake, Americans love eating meats. Meat is essential part of a healthy diet, but over consumption of meat will kill you. America spends hundred of billion dollars on meat and it’s no wonder why cancer is epidemic in United States. Meat is considered a luxury in other country’s, but meat in America is readily available anywhere and consumers need to learn self-restraint. Meat like hot dogs and bacon is part of American culture, but consumers need to understand that meat industry’s uses dangerous additives like sodium nitrate and eating it for a long period of time will have repercussion to your health. Strong evidence claims that not only the harmful sodium nitrate harms the body, but also eating meat in general will damage the body. There are other healthy options like non-meat protein. But the solution to the problem is consumers need to be aware of what they’re eating and learn self-restraint.

Mesosaurus Facts and Figures

Name: Mesosaurus (Greek for middle lizard); pronounced MAY-so-SORE-usHabitat: Swamps of Africa and South AmericaHistorical Period: Early Permian (300 million years ago)Size and Weight: About three feet long and 10-20 poundsDiet: Plankton and small marine organismsDistinguishing Characteristics: Slender, crocodile-like body; long tail About Mesosaurus Mesosaurus was the odd duck (if youll excuse the mixed species metaphor) among its fellow prehistoric reptiles of the early Permian period. For one thing, this slender creature was an anapsid reptile, meaning it did not have any characteristic openings on the sides of its skull, rather than a more common synapsid (a category that embraced the pelycosaurs, archosaurs and therapsids that preceded the dinosaurs; today, the only living anapsids are turtles and tortoises). And for another, Mesosaurus was one of the first reptiles to return to a partially aquatic lifestyle from its fully terrestrial forebears, like the prehistoric amphibians that preceded it by tens of millions of years. Anatomically, though, Mesosaurus was pretty much plain vanilla, looking a bit like a small, prehistoric crocodile... that is, if youre willing the overlook the thin teeth in its jaws that seem to have been used to filter plankton. Now that all thats been said, however, the most important thing about Mesosaurus is where it lived. The fossils of this prehistoric reptile have been discovered in eastern South America and southern Africa, and since Mesosaurus lived in freshwater lakes and rivers, it clearly couldnt have swum across the expanse of the southern Atlantic Ocean. For this reason, the existence of Mesosaurus helps support the theory of continental drift; that is, the now-well-attested fact that South America and Africa were joined together into the giant continent Gondwana 300 million years ago before the continental plates supporting them broke apart and drifted into their current positions. Mesosaurus is important for yet another reason: this is the earliest identified animal to have left amniote embryos in the fossil record. Its widely believed that amniote animals existed a few million years before Mesosaurus, only recently evolved from the first tetrapods to climb up onto dry land, but we have yet to discern any conclusive fossil evidence for these very early amniote embryos.