Patients saftey Thesis Example | Topics and Well Written Essays - 2000 words

Patients saftey - Thesis Example It does seem likely, however, that, under stress, hospital staff is more likely to make mistakes that can contribute to the emergence of accidents, because high stress levels can impair the level of concentration, cognitive information processing, decision-making and work behavior (Furney, Press). The main research question that guided the present study was whether objective work stressors and resources predict important characteristics of stressful events that are related to safety among novice nurses. The characteristics in question were the similarity of the particular event to previously experienced events and the probability that the event would recur in the future. Thus, the risk potential contained in the event was assessed in terms of the event being a recurrent rather than a singular event - either because it had occurred in the past and/or because it was estimated to have a high chance of recurrence. Work stressors and job control both assessed by observer ratings were respectively expected to be positively and negatively associated with the two indicators of risk potential. Work stress, especially work overload (e.g. by time pressure) has been shown to be associated with occupational accidents (e.g. Frone 1998, 565, Zohar 2000, 591) and medical malpractice (Jones et al. 1998, 730). Conversely, resources such as job autonomy or job control are positively related not only to health and productivity but also to safe working practices (Parker et al. 2001, 214). This study investigates the association between chronic job stressors and characteristics of safety-related stressful events encountered at work. Typically, in this kind of research, both predictors and dependent variables are assessed by means of self-report, and this presents a risk of overestimating the association because of correlated error (Semmer et al. 2004, 210). As such, many researchers recommend measuring independent and dependent variables with different methods

HUM310 Essay Example | Topics and Well Written Essays - 500 words

HUM310 - Essay Example eparated from the Anglican Church and perceived the New Frontiers a place where they could put up their roots and established their own institutions of the same. Bradfords journal documented these sentiments through absorbing story telling techniques so that the reader could relate to the sense of community, the struggle of the early settlers, and the peaceful manners in which the Native Americans and the Pilgrims embraced each other. Had it not been for this peaceful integration with the Natives, specifically the Wampanoag tribe, later settlers from England would not have been able to establish towns and cities so easily. Indeed, through Bradford eyes, the challenge of "self-definition and establishment" (Parini 7), the origin of many of American traditions and culture such as Thanksgiving, could be seen to have emerged to shape the new nation. Moreover, "Of Plymouth Plantation" demonstrated the importance of compromise and peacemaking in the process of making a nation. Instead, of concentrating on "wealth and adventure" alone, Bradford encouraged understanding of the Natives and communication. He believed in embracing the value the locals had to offer to the new settlers through "sacred bonds and ties" of the "sweet communion" (Parini 10). At the same time one gets the sense of change during the 17th century. Bradford was saddened by the humiliation that the new generation brought with it by their violent behaviors and willful desecration of the locals. He believed the new colonists dissipated the foundations that were built by the early settlers particularly the Pilgrims of Plymouth that took years in the making. Although, Parini (10) sometimes believed Bradford to have veered from actual historical events, nevertheless one could relate to Bradfords experience at the time which were different from the narratives of the later colonists who were fiercer, resistant and against the Natives. Their dispositions resulted in bloody wars and waste of precious lives

Bangladeshi Women in Bricklane Essay Example for Free

Bangladeshi Women in Bricklane Essay â€Å"I always said I will not marry and be sent far away. I will go no farther than these paddy fields. But our mother told us we must not run from our fate. What cannot be changed must be borne. The test of life is to endure.† Through such representation of gender and focus on history and dislocation, Monica Ali has extended the migrant voice in British fiction. In her stunningly accomplished debut novel Brick Lane (2003) which also got adapted in a film four years later, Ali tries to reconstitute the traditional Bangladeshi culture in a London East End setting. She uses her characters to explore the positioning of Bangladeshi women within Britain, as the novel focuses on their social relations inside and outside the home. This paper aims to explore whether Monica Ali’s novel Brick Lane (2003) and Sarah Gavron’s controversial screen adaptation of the same name (2007) can open up avenues to discuss a new, if problematic, inclusion of Bangladeshi women in the transnational world; and also to gauze the similarities and dissimilarities within the two. Both the novel and the film created a controversy among the Bangladeshi community living in London because they found problems with Monica Ali’s negative portrayal of their community members as being illiterate and backward, which they considered insulting. They claimed that the novel encouraged â€Å"pro-racist, anti-social stereotypes†. Brick Lane is the story of the Bangladeshi Muslim community living in the East End of London and in particular, that of Nazneen, her husband Chanu and Hasina, Nazneen’s good looking sister, who resides in Bangladesh and who was disowned by her family for flouting the traditional arranged marriage system which she did by eloping with her lover and marrying him at the age of sixteen. Hasina’s chaotic day to day life in Dhaka is revealed to us through a series of regular, candid and sometimes terribly despondent letters sent to her sister in London in pidgin English. Nazneen often reminisces about her happy, innocent and carefree childhood in her little village in the countryside of Bangladesh with her younger sister Hasina, which now contrasts with her despairing life in her dingy flat in a tall block in the Tower Hamlets. After an arranged marriage with Chanu, who is already established in London and who is unattractive and twice her age, Nazneen arrives in London at the age of seventeen. The women moving to London and Tower Hamlets in particular had to adapt coming from a rural peasant society to a hostile urban culture. What Brick Lane does is show this transition and the impact migration has on women’s lives. Monica Ali’s novel shows how, after migration, the position of women in families and in the wider community undergoes a considerable transformation. What Nazneen refuses to do is to see herself and her culture as inferior or alien. Here ethnicity becomes a source of positivity rather than stigmatised identity. The high rates of poverty characteristic of Bangladeshi households are shown in the novel, coupled with the overwhelming sense of isolation faced by the female characters and their reliance on their male counterparts. Consequently, the overall context of the novel presents a picture of deprivation and hardships for Bangladeshis in Britain. Nazneen who can’t speak English has to adapt to her new life in a foreign country with a husband who, although basically kind-hearted, is disheartened for not being able to fulfil his dreams and carry his plans to completion. He believes himself to be above most of the Bangladeshi community members who are uneducated and lacking a great deal of elegance. Chanu scorns the attitude of his superiors who fail to recognise his talent and genius. He keeps a high opinion of himself which makes him a conceited, funny character despite his lucidity and his awareness of the conflict between the first and second generation immigrant, which, to his horror, was portrayed by his eldest daughter Shahana and which made him decide to repatriate his entire family to Bangladesh. The novel is challenging in an overwhelming way the strong element of fate. Nazneen and Hasina are two characters through which Ali explores two images of femininity. Nazneen has been the good daughter who accepted an arranged marriage and her younger rebellious sister Hasina was the bad daughter who takes her fate into her own hands by eloping with the man she loved and was consequently disowned by her father. Nazneen accepted her fate yet Hasina rebelled to create her own. Hasina’s western-style attempt at romantic freedom, contradicts the traditional structures of Bangladeshi society within which she lives and within which her sister is immersed in the Diaspora. Both the sisters face problems settling with their husbands, and ultimately both have relationships with younger men. Though Nazneen carried out small rebellious acts at the beginning of her marriage, her aspiration for liberty started with her attraction to the handsome, young political enthusiast, Karim, which evolved into a physical and financial independence and the discovery of her freedom of choice in a patriarchal community. Nazneen is plain â€Å"not beautiful, but not so ugly either† and in contrast her sister Hasina is â€Å"beautiful and feisty†. (Ali 17). Hasina defines herself in contrast to the activities around her and Nazneen defines herself against the talkativeness of her husband. Through these transnational links, Nazneen and Hasina become embodiments of womanhood in two different but connected locations. Monica Ali endeavours to explore the impact of migration for those within the Bangladeshi Diaspora. Ali seems to suggest that within the context of Diaspora women are more Bangladeshi than the Bangladeshis in Bangladesh. We learn how those in Britain replicate the social practices and norms of Bangladesh so that the culture also migrates to Britain with the people: â€Å"through the open window, drifted wafts of music and snatches of currymain meals were cooked at all times of the day and night†. (Ali 189). Yet in contrast, those who remain in Bangladesh are adapting to the changes occurring in society. Hasina acts as if she is the person who has shifted geographically to another country. She appears more modern in her thinking in contrast to her sister, who appears more traditional. The two women placed within the two different localities also enable Ali to show how social practices and social relations change in the two locations. Within the context of Britain, Nazneen witnesses changes in the images of Bangladeshi femininity among her friends, who become more westernised. The seventeen-year old, once subdued and obedient wife, matures into a forthright independent woman. She discovers her own force and will power, something she was unaware of. She decides that she will no more be controlled by fate, she will take her own decisions, like not following her husband by going back to their homeland. She will remain in London, she will work and look after herself and her two daughters. She takes this decision because her daughters are way too comfortable in London, and they don’t want to go back ‘home’ to Bangladesh. London is ‘home’ for them, and that’s when Nazneen realized that she was seventeen when she came here and now she’s thirty-four, so she has lived half of her life here. This is home, and this is where her daughters want to be. This is where she found her independence and her voice in her own ways. She wears her sari. She has not started wearing trousers or cut her hair short. In her very own way, she has found a voice and she is comfortable with that here. Nazneen thus starts to believe in herself and realizes that she is capable of taking charge of her own destiny. The Bangladesh Nazneen refers to is different to other Bangladesh Hasina writes about in her letters. The contrasts between Tower hamlets and Bangladesh are shown, for example by the fact that Nazneen comes from an idyllic, warm, green environment quite unlike the England of dead grass, broken paving stones and net curtains. Hasina’s letters dispel the myth that Bangladesh is still rural. Rather it is now urban and violent. A more dangerous Bangladesh with corrupt politicians dominates the letters. Hasina describes to her sister how the garment girls have become branded as sexually immoral due to their working in close proximity to men. The patriarchal world of Bangladesh mirrors the patriarchy practiced within Britain, but is stronger. For example, Hasina, left without the protection of a husband, is raped, then forced to become a prostitute to survive and her friend (Monju) is murdered by her husband drenching her in acid. While Hasina works within a factory as a machinist, her sister, in the liberated environment of the West, also resorts to working as a machinist, but in purdah within the environs of home. For Nazneen, Britain is loaded with negativity, and it fails to accumulate the warmth and security she experienced in Bangladesh. Nazneen treats her loneliness through anti-depressants which baffles her sister: â€Å"I do not know what kind of pill can cure disease of sadness†. (Ali 143). Nazneen is disappointed with Britain and recollects Bangladesh with fondness, a nostalgia that provides the framework within which the story is located. Monica Ali uses the cluttered room where Nazneen lives as a metaphor for her protagonists’ state of mind. It becomes even more cluttered over the course of the novel. When Bangladesh is presented it is done so with space; however, the restrictiveness of England is stressed through the feelings of claustrophobia. Nazneen’s perception of Britain for much of the novel is not only contained within the environment of her flat, but also when she gazes out of her window. Her London is restricted to her locality: outside her window she sees â€Å"dead grass and broken paving stones† (Ali 12), â€Å"cycle racks which no one was foolhardy enough to use†, and round the corner is a playground that has shrunk to one decrepit roundabout. Nazneen evokes an image of Britain which is dark and grey and congested â€Å"a roaring metal army tearing up the road† (Ali 33). The poverty in Tower Hamlets is also emphasised if not exaggerated by Nazneen as she ventures out of the home, and â€Å"stepped over an empty cigarette carton, a brick and a syringe† (Ali 380). Although Nazneen’s husband Chanu has a degree from Dhaka University, they live in a grotty tower block in Tower Hamlets, where the paint flakes off the â€Å"eczema-ridden walls†. Poverty, socio-economic deprivation, dominates the social fabric of Ali’s Bangladeshi society in Tower Hamlets. This deprivation is also evoked through Nazneen smelling â€Å"the overflowing communal bins† (Ali 13). All the more, the Bangladesh that is reflected in British society angers Chanu, Nazneen’s husband, as it perpetuates a derogatory image of Bangladesh through education. He despairs over what his children are taught about Bangladesh: â€Å"all she knows is about flood and famine. Whole bloody country is just a bloody basket case to her† (Ali 151). Even the image that Shahana has of Bangladesh is old and traditional. As she tells her sister, â€Å"just wait until you’re in Bangladeshyou’ll be married off in no timeyour husband will keep you locked up in a little smelly room and make you weave carpets all day long† (Ali 329). â€Å"In Bangladesh you’ll have to brush your teeth with a twig. They don’t have toothbrushes†(Ali 331). Brick Lane is a contemporary, and humane story, the characters are shown with all their complexities and are described realistically and in detail whether it’s Mrs Islam, the hypochondriac, evil and manipulative usurer, or Razia the friendly and strong will-powered neighbour, or Shahana, the refractory, provocative and westernised teenage-daughter, or the sweet second daughter, little Bibi who is even tempered, quiet and hard working. It is a post-colonial novel written with a great deal of compassion and optimistic hope. Sarah Gavron’s film that was screened in 2007 is closely related to the book in terms of important aspects like casting, themes and plot. A long shot shows the central protagonist Nazneen (Tannishtha Chatterjee) disappearing behind one of the many front doors dotting the monolithic faà §ade of a public housing block in East Central London. This concludes a seven-minute prologue in which director Sarah Gavron condenses the first hundred pages and more of Monica Alis 2003 source novel. Digitally colorized shots of 1970s and 1980s Bangladesh indicate the extent to which Nazneen has idealized her memories of growing up in that time and place, her close relationship with younger sister Hasina (Zafreen) an especial source of reverie. A rural Bangladeshi childhood remembered as idyll ends, however, with the suicide of the girls mother. Consequently, their father arranges marriage between Nazneen, now a teenager, and the significantly older Chanu (Satish Kaushik), an immigrant living in London and a man she has never met. Some fifteen years later, thirty-something Nazneen is shown walking through and around Brick Lane, one of the most ethnically diverse neighbourhoods in the United Kingdom. Ghosting through a multicultural urban milieu radically different from that she was born into, she speaks to no one, slips ever further from the following camera, and disappears finally behind the front door of a flat as cramped and constricting as her monotonous existence—dutiful wife, mother, and nothing more. She is shown as raising two daughters: â€Å"Shahana† and â€Å"Bibi.† Bibi (Lana Rahman) is still young, sweet, and compliant, but Shahana (Naeema Begum) is a teenager with raging hormones and a sharp tongue. Nazneen and Chanus ossified marriage is changed irrevocably when the former buys a sewing machine. She does so through necessity as much as choice, driven by the need to financially support her family, husband, and daughters Shahana and Bibi , after Chanu resigns his job, disillusioned by his persistent failure to win promotion. Yet a purchase which seems initially to confirm Nazneens domestic incarceration yet further—not working from home but home as work—brings her into contact with British-born Karim (Christopher Simpson), the young man who delivers garments to her flat for finishing. She begins an affair with him, and the emotional and physical self-confidence this engenders allows Nazneen to assert, eventually, her presence and identity within the immediate family unit. Yet the seemingly clear-cut contrast between Karim and Chanu and the divergent futures they seem to promise Nazneen become more complicated as Brick Lane progresses. Karim comes to seem less attractive than at first, Chanu more so. The formers marked physical and cultural differences from the latter (young, fit, second-generation, British-Bangladeshi vs. old, fat, first-generation, Bangladeshi-British) cannot disguise the fact that he is equally inclined to idealize Nazneen as archetype not individual. Its Chanu who valorizes her as a living example of the ‘girl from the village’ in the early pages of Alis novel. Crucially, however, theres no interpretative violence in transferring those words to Karims mouth in Gavrons film. Meanwhile, Chanu is shown to possess significant redeeming qualities obscured by his complacent, corpulent exterior. He loves his family deeply and is horrified equally by the rise of Western anti-Muslim and Muslim anti-Western sentiment in the wake of 9/11. Chanu is able to view this process with far more humanistic caution and historical context than Karim can or will. Ultimately, Nazneen ends her affair with Karim, while Chanu agrees to return to Bangladesh on his own. Liberated, albeit not in the sense that Brick Lane seems initially to promise, Nazneen stays behind in London with her two daughters. Wider context—the effect of 9/11 on Western Muslims, the changing role and self-image of immigrant communities within contemporary British society, the ongoing, intergenerational debates about tradition, gender and religious identity within those groups—are all glimpsed fleetingly from Nazneens perspective. The main effect, though, is to impress upon viewers just how cloistered her vantage point is. Ultimately, Brick Lane temporarily imprisons the world-view of all who watch it behind bars made from net curtain. This is so even while the film ostensibly supports Nazneens quiet attempts to break free from something approaching a state of psychological house arrest. Brick Lane is a real place, and it’s been the centre of the British garment district ever since Huguenot refugees brought their looms from France in the early 18th century, followed by waves of poor Irishmen and Ashkenazi Jews. Brick Lane was however, filmed in the financial district that is synonymous with the books real location. The novel as compared to the film sets up the location more exotically like a mini version of Bangladesh, with the smells of spicy food, colourful fashions and emphasis on religion. For the film, one was expected to picture a colourful setting that transported the reader to another world. Though Brick Lane in the film does create its own world, it lacks the lustre brought out in the novel, and definitely was not reflecting any part of South Asia. The scenes in Bangladesh gave more of a contrast to London life, unlike the book, where Nazneen seems to still be tied to her homeland. The book documents her memories as if she had not left the village. For example, Nazneen does not leave the house, allowing her to limit her exposure to English culture. The film demonstrates a sharper contrast of her surroundings mostly through the addition of Nazneen leaving the flat to do the shopping. The shopping allows her more freedom and; thus, more information is acquired about England. The film effectively provided the atmosphere of Chanu and Nazneens flat. In the novel, Bangladesh provided richer local descriptions compared to London, because Nazneen did not dwell on the details of her flat. She only mentions some decorations. The film gives the opportunity to see the living arrangement in London from the complex she lives in with Chanu. The film emphasizes the close quarters and the weather to portray a cold representation of London, differing a lot from the vibrant frolicking in the lush and long Bangladeshi grass of the two sisters. Even at the end of the film, Nazneen is shown making snow angels with her daughters, as if she has conquered the cold. The casting was terrific. Chanu, Shahana and Bibi gave compelling performances that mirrored the characters in the book. Chanu especially is exactly the way one visualizes him on the basis of the novel. To understand Nazneen one had to make sure to read the novel because then one would know the thoughts in her head that she did not always say. Tannishtha Chatterjee, the actress who starred as Nazneen, faced a challenge in this role, because so much of the character was about not saying anything. Silence also played a big role in the film, which sometimes contributed to the action and other times made the movie too slow. The novel captivates the reader by the sensory details, mystical connections to Bangladesh, and curiosities about English culture. The film uses silence to provoke the audiences response to the vivid scenes in Bangladesh while also building up to the climax. Though the climax is not surprising to the reader or film goer, the novel was more effective in showing Nazneens struggle and confrontation with disaster. The novel created tensions leading up to Nazneens inability to react. The film on the other hand, relied too much on silence for plot points to emerge. The reader tends to miss Nazneen’s rebellion since it’s all done in silence. Overall, rebellion and freedom are downplayed in the film probably to emphasize the idea of fate. Hasina, Nazneens sister is the source of scandal in the novel and could have been more present in the film. She acts almost as a ghostly figure, sometimes only mentioned through voice, when Nazneen pictures her whispering in her ear. The film also glamorizes her experience in Bangladesh, as if she has the freedom to fall in love. The letters in the novel describe the opposite with violence to women and hard work conditions. In the film, Hasinas true situation is exposed by Chanu, who hears from his cousin that she has become a prostitute. However, then Nazneen falls ill, and the audience is left in confusing hallucinations, wondering if Chanu was trying to be mean to his wife or was actually speaking the truth. This inconsistency between reality and fantasy is evident in both the book and the film. Chanu glorifies Bangladesh in both the mediums. Nazneen reflects on her memories from her childhood in Bangladesh, but is grounded in the reality of London. For example, she cannot depend on Chanu to be responsible, when he cannot hold down a job and continues to insist that they will return to Dhaka. She does not point out his failures, the same way she does not point out Karims, but acknowledges her realistic priorities. Some include the disaster that Shahana would encounter in Bangladesh, and another would be breaking up with Karim and needing to be on her own. The American trailer of the film also illustrates this dichotomy, advertising the movie as more dramatic and scandalous. Perhaps the closeness of the text to the film adaptation is another way to enhance the themes of the original story. Much of Brick Lane takes place within Nazneens cluttered, unremarkable home, but this is rendered a fascinating, richly expressive setting through accomplished, considered use of technique by director Sarah Gavron and her key colleagues. Carefully calibrated expressionistic exaggerations of colour abound to communicate Nazneens largely unspoken inner life. Green sequins on a girls top reflect on her face to show her initial entrancement with Karim; sunlight filtered through gauzy red curtains turns the dingy prison of her marital bedroom into a boudoir when he occupies it with her. Likewise, Gavrons movement of camera and attention to framing are evocative and subtle in equal measure. If, as noted at the outset, one of the first shots in Brick Lane can be seen to sum up both the films project and a range of possible responses to it, something similar can be said of the movies final image. With Chanu back in Bangladesh, it is now winter in London. Nazneen and her daughters play joyfully in the snow-covered square at the front of their apartment block, inhabitants of a climate, and by extension a culture, diametrically opposed to the monsoon conditions the teenaged Nazneen and Hasina frolic in at the film’s early moments. A birds-eye aerial shot of mother and daughters lying on the ground, waving their arms and legs, cuts to a medium shot of Nazneen on her own. The reader might get the impression here that Nazneens unassuming victory is also Brick Lanes. She extricates herself from the oppressive expectations placed upon her by virtue of the body and respective cultures she was born and migrated into. So too the film respectfully declines the received agenda of responsibilities imposed upon it in light of its British Asian subject matter and cultural provenance. Brick Lane is not a film finely crafted and beautifully performed in order to mask or compensate for its evasion of inarguable ethno-political duties. Rather, its sensuous pleasures and humane insights expand the range of what the political might be, and rethink the relative scale on which it might be expected to loom, within an important tradition of contemporary British film. Thus, both the mediums, reciprocating each other, have successfully rendered the portrayal of Bangladeshi women in the transnational world with a subtlety and expertise that is seldom to be seen. WORKS CITED Ali, Monica. Brick Lane. Black Swan. Great Britain. (2003). Print. Brick Lane. Dir. Sarah Gavron. Perf. Tannishtha Chatterjee, Satish Kaushik and Christopher Simpson. Ruby Films.(2007). Film. Lea, Richard and Lewis, Paul. â€Å"Local protests over Brick Lane film†. Gaurdian. (Monday 17 July,2006). Web. http://www.guardian.co.uk/books/2006/jul/17/film.uk Hussain, Yasmin. Writing Diaspora: South Asian Women, Culture and Ethnicity. Ashgate Publishing Ltd. England. (2005). Print. McLeod, John. The Routledge Companion to Postcolonial Studies. Routledge. London. (2007). Print. Mukherjee, Meenakshi and Trivedi, Harish. Interrogating Post-Colonialism: Theory, Text and Context. Indian Institute of Advanced Study. Shimla. (1989). Print. Sinha, Sunita. Post-Colonial Women Writers: New Perspectives. Atlantic Publishers Distributors (P) Ltd. New Delhi. (2008). Print.

The Mid-Autumn Festival: History and Features

The Mid-Autumn Festival: History and Features Introduction The Mid-Autumn Festival also known as the Mooncake Festival or the Festival of Lanterns is one of the most important traditional Chinese festivals, celebrated by many Asian countries, like China, Taiwan, Japan, Vietnam, Korea, Malaysia, and Singapore. This report is divided into three main sections. It will first look at the history and legends of the Mid-Autumn Festival. It will then focus on the celebration in Taiwan. Then there will be a conclusion in the last part. The information of this report is come from website such as online library, university journal, and online news. In this report I will use the information which is from online library, and university journal to explain the background as these information is more trustable. The information from online news is used to explain the celebration in Taiwan because it reflects what we do and the meaning for us nowadays. History and legends of the Mid-Autumn Festival The everyday life of ancient Chinese is closely related to nature. In thousands of natural substances, the moon was one of the most difficult things and amazing phenomena for Chinese to comprehend. (Siu, 1999) Ancient Chinese believes that the life of plants was provided by the moon since they found out that plants grew at night. (Siu, 1999) In addition people could not explain why the shape of the moon always varied therefore ancient Chinese associated the phenomena to the lives of people and animals. (Siu, 1999) The Mid-Autumn Festival is on the 15th of the 8th lunar month and the moon is at its brightest, roundest and it is the nearest to the earth on this date. In fact autumn is also the best time for harvesting and gathering all the family members together to celebrate the harvest and enjoy the view of the moon. (Tan, 2004) The festival probably started off as a post-autumn harvest celebration more than 2,000 years ago. The celebrations were devoted to giving thanks to the gods. It was during the reign of Emperor Tai Tsung of the Song Dynasty that the 15th day of the 8th moon was set as the Mid-Autumn Festival and praying to the moon became popular. Legends associated with the full moon were later attached to this festival.  (Tan, 2004) There are two legends associated with the Mid-Autumn Festival. One of them is Hou Yi and Chang-E and the other one is the rabbit on the moon. (Tan, 2004) The legend of Hou Yi and Chang-E is talking about that the earth was saved from scorching by an archer, Hou Yi who shot nine suns that originally circled the earth. (Tan, 2004) After Hou Yi saved the world he was rewarded the elixir of life so that he got the endless lifetime with the elixir, however he became so tyrannical that his wife, Chang-E stole the elixir and drank it to end Hou Yis life for the sufferers who were ruled by Hou Yi. (Tan, 2004) Chang-E found that she was on the moon after she drank the elixir and was escalated to status of Moon Goddess as she save the sufferers from Hou Yi. (Tan, 2004) This legend is believed to have been started during the Tang Dynasty (618 907 AD) although some believe it may have started earlier, tracing it to the rule of Emperor Yuan (2346 BC). (Tan, 2004) The other legend is about a rabb it and Buddha who had pretended himself as a hungry old man and asked three animals; a fox, a monkey, and a rabbit, getting some food for him. (Tan, 2004) Instead of bringing a fish or fruits, the rabbit jumped into the fire and offered itself as meat to Buddha. (Tan, 2004) The rabbit was resurrected and sent to the moon to be venerated by Buddha with appreciation. (Tan, 2004) Nowadays Chang-E and lord rabbit are traditional icons of the Mid-Autumn Festival as we can see a lot of advertisement of moon cake with these two icons which remind us these two legends. The Mid-Autumn Festival celebration in Taiwan In Taiwan, there are three biggest celebrations; the Chinese New Year, the Dragon Boat Festival, and the Mid-Autumn Festival which is also called Zhong Qiu Jie in Mandarin. (Yeo, 2012) The Mid-Autumn Festival was brought to Taiwan by the immigrants from China. (Wang, 2014) Many Western concepts that include barbecue were imported into Taiwan during the period of the Japanese colonization of Taiwan by the Japanese government. (Wang, 2014) After 1945 a lot of people moved into the city for jobs from the countryside. On the Mid-Autumn Festival barbecue becomes to be the best way for these migrants to make the new relationship between the migrants closer because barbecue is an activity that needs everyones cooperation from lighting a fire, preparing the meat, and barbecuing. (Wang, 2014) Even nowadays on the Mid-Autumn Festival, most Taiwanese will barbecue with their friends since it is easier to meet up with friends on this Taiwan-declared public holiday instead of at weekdays. (Yeo, 2 012) Besides mooncakes is also very important on the Mid-Autumn Festival. This traditional dessert is usually packed as gift boxes which contain not only mooncakes but also other pastries such asluo buo si bing (radish pastry) and gui yuan dan gao (longan cake) to up the warmth of the festival. (Yeo, 2012) Conclusion As one of the most important traditional festival in Chinese, the Mid-Autumn Festival is full of historical and cultural meaning. In addition it gives people a chance to meet up with friends and families to enjoy the beautiful view of the brightest moon and delicious barbecue and mooncakes in this busy society. The round image of the moon and its cultural meaning of reunion make us cherish the time of gathering. Even though not everyone can get together with their friends and families especially for those people who are working or studying in foreign countries, the Mid-Autumn Festival still reminds these people to send their friends and families a massage to show how they miss each other. Reference list Siu, K.W.M. (1999). Lanterns of the Mid-Autumn Festival: A Reflection of Hong Kong Cultural Change (pp. 67).Retrieved from Wiley Online Library. http://onlinelibrary.wiley.com/doi/10.1111/j.0022-3840.1999.3302_67.x/abstract Tan, B. (2004). Mooncake Festival (Zhong Qiu Jie). Retrieved from National Library Board Singapore. http://eresources.nlb.gov.sg/infopedia/articles/SIP_804_2005-01-13.html Yeo, J. (2012, September 20). Traditional BBQ for Mid-Autumn Festival ? Yahoo Lifestyle. Retrieved from https://sg.style.yahoo.com/news/traditional-bbq-mid-autumn-festival-132534304.html Wang, C. (2014). The Barbecue in Moon Festival: Discussing the Social Change of Moon Festival Activities (pp.93-110). Retrieved from Chung Hsing Journal Humanities Edition. http://ir.lib.nchu.edu.tw/bitstream/11455/88022/1/85470-3.pdf

The Central Processing Unit :: essays research papers

The Central Processing Unit Microprocessors, also called central processing units (CPUs), are frequently described as the "brains" of a computer, because they act as the central control for the processing of data in personal computers (PCs) and other computers. Chipsets perform logic functions in computers based on Intel processors. Motherboards combine Intel microprocessors and chipsets to form the basic subsystem of a PC. Because it's part of every one of your computer's functions, it takes a fast processor to make a fast PC. These processors are all made of transistors. The first transistor was created in 1947 by a team of scientists at Bell Laboratories in New Jersey. Ever since 1947 transistors have shrunk dramitically in size enabling more and more to be placed on each single chip. The transistor was not the only thing that had to be developed before a true CPU could be produced. There also had to be some type of surface to assemble the transistors together on. The first chip made of semiconducitve material or silicon was invented in 1958 by Jack Kilby of Texas Instruments. Now we have the major elements needed to produce a CPU. In 1965 a company by the name of Intel was formed and they began to produce CPU's shortly thereafter. Gordon Moore, one of the founders of Intel, predicted that the number of transistor placed on each CPU would double every 18 months or so. This sounds almost impossible, however this has been a very accutate estimation of the evolution of CPUs. Intel introduced their first processor, a 4004, in November of 1971. This first processor had a clock speed of 108 kilohertz and 2,300 transistors. It was used mainly for simple arithmetic manipulation such as in a calculator. Ever since this first processor was introduced the market has done nothing but soared to unbelievable highs. The first processor common in personal computers was the 8088. This processor was introduced in June of 1978. It could be purchased in three different clock speeds starting at 5 Megahertz and going up to 10 Megahertz. This CPU had 29,000 transistors. Then came the 80286 and 80386 processors. The 386 was the first processor to be introduced in the DX, SX, and SL versions. Next came the 80486 processors of which there were even more choices here. The first 486 processor had 1,200,000 transistors and the latest have 1.4 million transistors. There clock speeds varied any where from 16 MHz on the first ones to 100 MHz on the most recent 486 processors. Some of which are still in use in homes all around the country.

Gaelic League :: Essays Papers

Gaelic League What are the Irish known for? Most people would automatically think of some trivial fact about something like the potato famine, others the stereotypical views of the Irish drinking habits, and undoubtedly good old Irish American pubs would definitely come to mind. Although these are definitely interesting parts of the Irish history there are many other aspects to this unique heritage that truly capture the spirit of the Irish tradition. The Gaelic League was started with the founding of the Gaelic Athletic Association. This group founded in 1884 in attempts to promote and maintain Irish sports, helped to spawn the idea of Irish nationalism which eventually personified itself into organizations such as the Gaelic League. The Gaelic League was founded in 1893 by Douglas Hyde and Ed MacNeil to spread the Irish language (Hachey and McCaffery 14). Formed in Barnesmore where language classes were held in the national school; the support of both Catholics and Protestants made it poss ible to branch off to other areas (O’Connor 37). After the devastation of the potato famine and the implications of the home rule; both the Gaelic League and its predecessor the Gaelic Athletic Association had the common goal of bringing forth Irish nationalism in a country that desperately needed national pride. This movement for national pride had some success, but not before the failure that preceded it. There are a few reasons that this move, for national pride, produced failure one was the reputation of the Irish and another was the pressure of politics put on the different associations. The Irish language was considered to be a peasant’s language (O’Connor 87). Because of this the people of country that were poor and not educated in the language did not think it was worth spending money to learn. Tthe people in the country that had the money to learn the language normally did not want to learn the language for the mere fact it was considered to be a peasants language. Another reason for some of the failure that this movement attained is due to the political pressure created because of the nature of the movement itself. The two founders of the Gaelic League Hyde and McNeil never wanted the movement to become political (Gavin 56). However, this was inevitable. The mo vement caused a split in the people, those who were educated in the language and those who were not educated in the language (Hopkins 129).

Restricted Earth Fault Protection

A Comparison Between High-Impedance and Low-Impedance Restricted Earth-Fault Transformer Protection Casper Labuschagne, Schweitzer Engineering Laboratories, Inc. Izak van der Merwe, Eskom Enterprises Abstract—Restricted earth-fault (REF) protection on a transformer is a subject for which there has been little attention and, compared to other types of protection, very little literature exists. Depending on the method of transformer earthing and fault location, some transformer earth faults result in only a small increase in phase current, which transformer differential protection may not detect.Conversely, the amount of current in the neutral may be sufficient to detect most or all earth faults, again depending on the earthing method. By connecting an REF relay to CTs installed in correct locations on the transformer, one can use REF protection to complement differential protection in detecting transformer earth faults. Obtaining maximum benefit from REF protection requires tha t one consider many factors, including whether to select high-impedance REF or lowimpedance REF relays. In making this selection, one should understand the theory behind each option.Historically, only high-impedance REF protection was available, because of equipment and technology limitations. Today, numerical protection relays include low-impedance REF elements for transformer protection. Both types of protection have advantages and disadvantages; the relays do not perform equally well in all applications. One key advantage of low-impedance REF protection included in a numerical relay is the ability to use CTs with different ratios and specifications without the need for interposing CTs.One key advantage of high-impedance REF is proven immunity (relay security) to CT saturation for external faults. Key to either type of protection is the ability to provide maximum winding coverage against earth faults. There is also speculation, as yet unsubstantiated, that a high-impedance REF ele ment provides superior sensitivity and coverage against earth faults. This paper summarizes the theory of classical high-impedance REF protection and new low-impedance REF protection.It also discusses issues such as relay sensitivity requirements, transformer fault current distribution, impact of fault location on relay performance (winding coverage), CT requirements, the impact of CT saturation response on REF protection elements, and application considerations for the two protection methods. current changes very little, but large current flows in the neutral conductor [1] [2]. REF takes advantage of the large current in the neutral conductor to provide sensitive and fast protection for transformer faults close to the earth point.REF protection applied to transformers may be referred to as â€Å"unit earth-fault protection,† and the â€Å"restricted† part of the earth-fault protection refers to an area defined between two CTs. Generally, REF protection can be applied in one form or another to all transformer windings, even delta-connected windings (see Delta Winding—NEC/R Earthed). On solidly earthed star windings, we will show that fault coverage is possible from the first turn above the star point, provided the REF element connects to a CT in the transformer neutral.This high winding coverage is possible because the relay operates on the high fault current in the neutral conductor instead of on the small fault current in the phase. On an unearthed star winding or a delta-connected winding without a neutral earthing compensator (NEC), winding coverage is reduced because of the lack of a neutral CT. Unearthed star windings or delta-connected winding installations provide phase CTs only (see Delta Winding—NEC/R Earthed), and the REF element operates on the change in phase current only. II. EARTH-FAULT CURRENT AND IMPACT ON SENSITIVITY A.Earth-Fault Currents in a Transformer for Different Connections When operating from the neutral C T, REF protection provides more sensitive earth-fault protection than does biased current differential protection. However, many setting engineers are uncertain as to the exact increase in sensitivity that REF protection provides. It is therefore necessary to quantify what one means by â€Å"more sensitive. † In the following discussion, we investigate the available fault current for star windings (solidly earthed, impedance earthed, and unearthed) and delta windings. ) Star Winding—Solidly Earthed For a solidly earthed star winding, an earth fault anywhere on the winding is similar to an autotransformer with a fault on the secondary side. Fig. 1 explains the phenomenon. I. INTRODUCTION Power transformers constitute the single most expensive item of primary plant in a substation. To protect this investment properly, transformer protection schemes contain a combination of protection elements, with biased differential protection widely used. Although biased ifferential p rotection provides excellent protection for phase-to-phase and most phase-to-earth winding faults, this element is less sensitive for single-phase-to-earth faults close to the earth point in solidly earthed transformers [1], [2], and [3]. For these faults, phase 2 NS x 14 Current (per unit) x Nc In In 12 10 8 6 4 Neutral Current Phase Current Fig. 1 Solidly Earthed Star-Connected Windings With Earth Fault X Per Unit From the Neutral 2 10 20 30 40 50 60 70 80 90 From Fig. 1, it can be seen that the turns ratio (TR) is as follows: TR = and In N + Ns 1 = c = Ip Nc xDistance of fault from neutral (percent of winding) Fig. 2 Neutral Current vs. Distance From Star Point in a Solidly Earthed HV Star Transformer (1) I n = I p †¢ TR = Ip x (2) Where Nc = the number of turns on the common winding (on the shorted part of the winding) NS = the number of turns on the series winding (on the healthy part of the winding) x = the distance from the neutral (p. u. ) Ip = primary side current In = fault current Therefore, for faults close to the neutral (when x is very small, on the order of 0. 1 p. u. ), the current flowing in the neutral is In = Ip/0. 1 = 10 †¢ Ip.Clearly, the change in neutral current is much greater than the change in phase current. Fig. 2 shows the difference in neutral current and phase current, plotted as a function of the fault distance from the neutral point [1] [2] [3] [4]. This curve was obtained from tests that were performed on a solidly earthed star transformer. (Because results vary for different transformer designs, the authors were unable to locate a formula that accurately describes the theoretical earth-fault current for all transformers). Fig. 2 shows that the neutral current (that also flows through the neutral CT) is always very high, in excess of 5 to 6 p. . For faults closer to the phase terminal of the star winding, there is reduced current contribution from the transformer neutral. Relay sensitivity is still not compromised, be cause the operating current through the relay is the sum of the neutral and phase current, with the phase current now higher than for faults near the neutral. Therefore, in the case of a solidly earthed star winding, relay sensitivity is not a problem for faults near the neutral because there is always sufficient current flowing in the neutral CT and through the relay and varistor to ensure relay operation. ) Star Winding—Resistance Earthed In the case of a resistance-earthed star winding, the relationship between fault location and fault current is linear, and the value of the earthing resistance determines the amount of fault current. From Fig. 1, assuming that the neutral is earthed through a resistor, we can see that the following is true: In = x †¢V 3†¢R (3) Where In = fault current x = the distance from the neutral V = the healthy phase-to-phase voltage R = the value of the earthing resistor Equation 3 presents a linear relationship between the fault location and the neutral current available to operate the relay.For small values of x, In is small and there may not be sufficient current to operate the relay. Therefore, for a resistanceearthed star winding, relay sensitivity is important for faults near the neutral. The value of x where the relay will begin operation is related directly to the relay operating current and the CT characteristics, i. e. , how much magnetizing current the CTs on the healthy phases will require. 3) Delta Winding—NEC/R Earthed In the case of a delta winding, there is always sufficient voltage to drive fault current through the fault and NEC/R.In theory, there is always at least half the phase-to-earth voltage available to drive the fault. This results in sufficient fault current, and relay sensitivity is not an issue [3]. 3 Because delta-connected windings do not have a star point, you can use the so-called balanced earth-fault connection or hybrid REF protection function in cases where the source is on the delta side of the transformer. In this case, the neutral CT is excluded from the circuit and the three-phase CTs are all connected in parallel with the relay element.The zone of protection is still only the delta winding of the transformer. The balanced earth-fault connection may also be applied to an unearthed star winding. III. RESTRICTED EARTH-FAULT PROTECTION THEORY To apply REF protection on star-connected transformers, connect the three-phase CTs in star, and connect this combination to a CT in the neutral leg of the transformer, NER or NEC, as shown in Fig. 3. These CT connections provide a path for the zero-phase sequence currents to circulate in the CTs during external faults, but they force the current through the relay for internal faults.Therefore, the REF relay provides protection for all earth faults that fall in the area between the phase and neutral CTs. Any fault outside this area should be covered by alternative protection functions. Red White Blue IFp Inp Ins Relay Ins Fig. 5 Internal Fault Indicating Operation on a Delta Winding With NEC A hybrid REF protection function may also be applied to a delta winding without an NEC. The hybrid REF excludes the neutral CT from the circuit and the three phase CTs are all connected in parallel with the relay element. This is called a balanced earth-fault connection.The zone of protection is still only the delta winding of the transformer. The hybrid REF function can also be applied to an unearthed star winding. A. High-Impedance REF Relay Element The high-impedance REF relay is normally a currentoperated relay with a resistor in series that provides stabilization. Generally, it may be one of two different types. The first type has internal resistors and has a voltage setting. In this type, the resistors are effectively switched in and out to change the setting and therefore the value of the stabilizing voltage.The second type has an external variable resistor where the setting is calculated in ohms and applied by changing the resistance of the variable resistor. 1) Design Considerations A number of design considerations must be taken into consideration when designing a high-impedance REF scheme. The most important considerations are described here: †¢ The ratio of the phase and neutral CTs must always be the same. †¢ In general, the CTs should have the same saturation characteristics. †¢ The kneepoint voltage must be higher than the stabilization voltage for external faults. The voltage across the relay and CTs (all in parallel) should be kept at safe levels while still being sufficiently high to allow operation of the relay when required. The magnetizing current of the CTs depends on the voltage across it, but too high a voltage results in higher magnetizing current that leads to a less sensitive scheme. †¢ In most cases, a metal oxide varistor (MOV) or surge arrestor is connected across the parallel connection of the CTs and relay to clamp the voltage to a safe limit, without affecting relay operation.The MOV protects the relay against high voltages developed during inzone faults. Sufficient current still flows through the relay to ensure operation [5]. Relay Relay Fig. 3 Basic Design of an REF Function Fig. 4 shows an external earth fault on the star (source) side of a transformer, and Fig. 5 shows an in-zone fault on the delta side of a transformer. Currents are in per unit. In Fig. 4, the zero-sequence infeed for an upstream red phase-to-earth fault circulates between the neutral CT and the red-phase CT, and no operating current can flow through the relay element.In Fig. 5, in the case of the in-zone fault on the delta winding, it is clear that all the fault current flows through the neutral CT (IFp = Inp) and nothing flows in the phase CT. Therefore, the secondary CT current has to flow through the relay element for this element to operate. At this stage, we simplify the scenario by not taking into account the magnetization of the other CTs. Red White Blue IF Relay IF – Inp Inp Ins Inp Inp Ins Fig. 4 ing External Fault Indicating Relay Stability on a Star-Connected Wind- 2) Setting Considerations The high-impedance REF scheme is set such that it is stable for a maximum through fault with one of the CTs completely saturated. Calculate VS, the stabilizing voltage, as follows: Vs = I f max †¢ ( RCT + RL ) n (4) Another important factor in the design of an REF scheme is the minimum allowable knee-point voltage of the phase and neutral CTs. This value is necessary during the design phase of the high-impedance REF scheme to ensure adequately specified CTs.To ensure that the CT does not saturate at the operating voltage, many engineers use a safety factor of 2. The knee-point voltage can be calculated as follows: Where Vs = the stabilizing voltage Ifmax = the maximum through-fault current detectable by the relay RCT = the winding resistance of the CT RL = the total lead resistance of the longest cond uctor between the relay and neutral or phase CTs n = the turns ratio of the CT In cases where the earth-fault current is limited through an NER or NEC/R, use the three-phase fault current as the maximum condition.With all four CTs of the same ratio, we expect the phase CTs (not the neutral CT) to saturate for external faults, because the three-phase fault current is higher than the earth-fault current. Therefore, we can ignore the resistance of the leads between the saturated phase CT and the relay. (The saturated phase CT and the relay are not necessarily near each other, so the lead resistances between them are not negligible). Phase CTs are generally located in close proximity to one another, so lead resistances between these CTs are negligible.VS is the value of the stabilizing voltage across the relay for maximum through-fault current and one saturated CT. The relay setting, Vset, is still unknown. If the voltage applied to the relay exceeds Vset, we expect the relay to operate . The most sensitive setting that can be applied is Vset = VS. Because network parameters change (higher fault current for example), Vset is usually selected higher than VS to allow for a safety margin. To ensure greater stability, one would select relay operating current greater than the sum of the healthy phase CT magnetizing currents at the set voltage.This ensures that the largest part of the secondary side fault current is used for the purpose of operating the relay and that less current is used for magnetizing the CTs on the healthy phases. Any mismatch in CT ratio will result in spill current, part of which will flow through the relay. Spill current cannot be related to current that flows on the primary side and flows on the secondary side. It may, therefore, cause the flow of â€Å"fictitious† current that results from CT inaccuracy.Not all spill current will necessarily flow through the relay; some of the current also flows through CTs (phase and/or neutral) not carr ying primary fault current. Effectively, the spill current flowing through the relay raises the voltage across the relay and CTs, causing more magnetizing current to flow. In the case of a through fault, equilibrium is reached between the voltage, relay current, and magnetizing current. Generally, relay current is far less than the operating current, as explained in the calculation of the stabilizing voltage. Vk = 2 †¢ Vs (5)Where Vk = the kneepoint voltage of the CT Calculate Iop, the minimum primary operating current (primary sensitivity) that causes the relay to operate, as follows: I op = n †¢ ( I R + m †¢ I m + I v ) (6) Where IR = the relay operating current m = the number of CTs needing magnetization (generally three) Im = the magnetizing current at the set voltage (to be obtained from the magnetizing curve test results of the CTs) Iv = the varistor current at Vs [5] From this discussion, it should be clear that the desensitizing factors are the magnetizing cur rent Im and the varistor current Iv.Use Equation 7 to calculate the actual impedance of the REF element. Because Vset is the voltage above which the relay operates, and because the relay resistance is much greater than RCT and RL, you can calculate the relay resistance as follows: RR = Vset IR (7) Where RR = the relay resistance Vset and IR are as defined above To verify correct calculation of operating current, it is possible to calculate the voltage across the relay for a specific inzone fault current. If the voltage is above the set voltage, consider this as confirmation that the relay will operate.You can calculate the operating voltage as follows: (8) n Because the relay is set to be stable under conditions where one CT saturates, it needs no additional time delays to improve security or its operation. B. Low-Impedance REF Relay Element Low-impedance REF protection is provided with new numerical or microprocessor-based protection relays. Generally, relay manufacturers employ di fferent methods to provide REF protection. In most cases, operation of the low-impedance REF protection is based on the fundamental current, after filtering removes all harmonic currents [3]. Vop = ( I op ? †¢ n †¢ I m ? I v ) †¢ ( RCT + RL + RR ) 5 The most important difference between classical highimpedance REF protection and new low-impedance REF protection is the input impedance. As with all numerical relays, the input impedance of the low-impedance REF is very low compared to high-impedance relays. For example, a lowimpedance relay typically has an input impedance of 0. 1 VA. At 1 A nominal rating, this computes to 0. 1 W. On the other hand, for a high-impedance REF relay with a voltage setting of 100 V and a 20 mA operating current, the input impedance is 5 kW. This is a significant difference.Low-impedance REF protection does not have the same inherent stability against CT saturation for external faults as does high-impedance REF protection. A second significa nt difference is that the operating current of the low-impedance REF protection is not realized by CT connection. With low-impedance REF, the relay measures all four CTs necessary to realize the element. Fig. 6 and Fig. 7 show the wiring and CT connections of the low-impedance REF elements. Fig. 6 shows the fault currents for an external fault on the primary star-connected side of a transformer, and Fig. shows an external fault on the secondary deltaconnected side of the transformer. Inp Red White Blue Ins IF + A Red White Blue Ins + A Inp Ins + Fault IF + B + C N Ins Inp IF – Inp Inp Fig. 8 Low-Impedance REF Connections With Internal Earth Fault on a Star-Connected Winding Red White Blue + + C B A IF Fault IF Ins N Ins Fig. 9 Low-Impedance REF Connections With Internal Earth Fault on a Delta-Connected Winding With NEC + B + C + IF – Inp Inp Fault Location B N Ins Inp Fig. 6 Low-Impedance REF Connections With External Earth Fault on a Star-Connected WindingA very impor tant advantage of low-impedance REF protection is the fact that the CT ratios for the phase CTs and neutral CTs do not have to be the same. Most low-impedance REF relays use an operating and a restraint current. The difference between different relays from different manufacturers lies in the way these relays determine the restraint quantities and in the CT saturation detection algorithm of each relay. Note that, in the case of low-impedance REF protection, there is no inherent immunity to CT saturation, as is the case with high-impedance REF protection.The following different methods are used to determine the restraint and operating current: Use of the residual current Ir = Ia + Ib + Ic as the restraint current and the differential current Id = Ia + Ib + Ic – In as the operating current. (9) 2. Use of the residual current Ir = Ia + Ib + Ic as the operating current and the neutral current In as the restraint current. (10) From Fig. 7, it may be seen that Ia = Ib = 0 for a blue -phase out-of-zone fault on the delta side of the transformer. From this, it is clear that |Ic| = |IF| = |Ins|.From Equation 9 above, one can see that the differential current can be defined as follows: Id = Ia + Ib + Ic – In = 0 + 0 +(–Ins) – (–Ins) = 0 and Ir = Ia + Ib + Ic = –Ins This shows clearly that there is restraint current but no differential or operating current for an external fault. From Equation 9 it can be shown that the following relationships are true: Id = Ins and Ir = 0 1. Ins C + B + A Ins IF N IF Fault Location Fig. 7 Low-Impedance REF Connections With External Earth Fault on a Delta-Connected Winding With NEC Fig. 8 and Fig. 9 show the same relay and CT connections for a low-impedance REF relay.They also show the current flow for in-zone faults on the primary star-connected and secondary delta-connected sides of the transformer, respectively. 6 This means that, while there is a large amount of differential or operating current , there is no restraining current. This can be shown similarly for in-zone and external faults on the star side of the transformer. Because of the nature of the protection, classical lowimpedance REF protection cannot be used as a balanced earthfault protection on an unearthed transformer or on a transformer with only three phase CTs and no neutral CT.In short, it is because the low-impedance REF protection requires a restraint and an operating current, at least one of which is also derived from the neutral CT. When a neutral CT is not provided, a low-impedance REF protection cannot be used to protect an unearthed transformer. However, most numerical relays provide a number of protection elements for each winding. To realize balanced earth-fault protection on an unearthed star-connected transformer or a delta-connected transformer, connect the CTs as explained under Delta Winding—NEC/R Earthed, and associate the CT input with an earth-fault element in the relay. ) Design Cons iderations Because of the inherently unstable nature of the lowimpedance REF element, it may misoperate during external faults, especially in the case of faults not involving earth as phase-to-phase and three-phase faults, when one of the phase CTs saturates. Various manufacturers of REF protection relays have each developed additional supervision elements to improve security during external faults while improving sensitivity during in-zone faults. All these relays scale the CT ratios automatically between the phase and neutral CTs to compare the different values on an equal basis. ) Product A [6] [7] This relay makes use of the direction change of the operating current for in-zone and external faults. It derives a zerosequence operating current from the phase CTs (Ir = Ia + Ib + Ic) and a polarizing current from the neutral CT (In). It then compares the direction of operating (Ir) and polarizing (In) currents. CT saturation logic is necessary to determine whether any existing zero- sequence operating current is from saturation of one or more CTs during a three-phase fault, or from an actual earth fault. CT saturation detection comes from a positivesequence restraint factor supervising the REF operation.The relay compares the positive-sequence current multiplied by the positive-sequence restraint factor (generally set to approximately 0. 1) with the zero-sequence operating current. For earth faults, the positive-sequence and zero-sequence currents are equal, so the result of this comparison will always be a logical 0, indicating no CT saturation. If zero-sequence exists as a result of CT saturation, CT saturation detection asserts whenever the ratio of zero-sequence to positive-sequence current is less than the positive-sequence restraint factor.Using the reasoning that current must flow in the transformer neutral for an earth fault, the relay enables the REF element only if the neutral current exceeds a threshold. Supervising the REF element with the neutral c urrent provides additional security against zero-sequence current in the line CTs resulting from CT saturation. Therefore, the relay enables the REF element only if the line CTs measure zero-sequence current and if the current in the neutral CT exceeds a pickup setting. The zero-sequence current pickup setting is therefore also the relay sensitivity.The zero-sequence pickup must be set higher than any natural zero-sequence current caused by load, CT mismatch/spill current, or any other unbalance. The minimum operating current of the relay is 5 percent of rated current (In). The directional element then compares the operating (residual phase current) and polarizing (neutral) currents and indicates a forward or reverse direction. A forward direction indication is for an in-zone fault, and a reverse direction is for an external fault.The fault is said to be in-zone when the residual and neutral currents are in phase; it is reversed if the residual and neutral currents are 180 ° out o f phase. b) Product B The basic principle of operation for this relay is to compare the residual (restraint) current Ir = Ia + Ib + Ic with the differential current Id = Ia + Ib + Ic – In, Where Ia, Ib, and Ic = the respective phase currents the neutral current flowing in the transIn = former as a result of the fault The relay compensates internally for the difference in CT ratios between phase and neutral CTs.In addition, the relay has a biased differential characteristic that you can set in such a way that the relay is desensitized for big differences in CT specifications and subsequent quiescent spill current under normal load conditions. In this case, the relay achieves stability for a through fault by increasing the restraint current when it detects a fault. The bias setting should still be set as sensitive as possible to ensure relay operation for most faults. The biased differential characteristic of this relay has a fixed slope of 1. 05 p. u. The relay will trip if 1) Id / Ir exceeds 1. 5 and 2) Id exceeds the Id pickup or threshold setting. The purpose of the restraint function is to compensate for CT errors and mismatches and to ensure stability during maximum through-fault conditions. The latter may cause CT saturation, and the bias characteristic provides additional stability against CT saturation. The relay has a minimum operating current of 5 percent of nominal current, or 0. 05 In. c) Product C [8] Similarly to Product A above, this relay uses the residual current calculated from the three phase CTs where Ir = Ia + Ib + Ic and the neutral current In for the REF protection.During an in-zone fault, neutral current will always flow irrespective of the transformer winding connection and earthing arrangement. The residual current depends on the transformer winding connection and earthing arrangement. In this case, if residual current exists, it will be in phase with the neutral current. During an external fault, the neutral and residual curren ts will be equal in magnitude and 180 ° out of phase. The relay uses In only as the operating current, and this current is always present during an in-zone fault. The relay pro- 7 ides a stabilizing method for CT saturation for through faults. Both the current magnitude and phase of the residual and neutral currents stabilize the REF protection. The stabilizing or restraint current is defined as follows: I res = k †¢ (| 3I n ? 3I r | ? | 3I n + 3I r |) (11) Where k = a stabilization factor In and Ir are as defined previously An examination of Equation 11 for both internal and external faults reveals that there is no effective restraint for internal faults because the value of restraint is always negative for internal faults.Therefore, the relay has maximum sensitivity, and small earth-fault currents can cause tripping of REF protection. The restraint for external faults is always positive and larger than the operating current, if the operating and restraint quantities are eit her in phase or 180 ° out of phase. During CT saturation, these angles may be different, resulting in reduced restraint for external faults. To prevent reduction of restraint, the relay calculates the angle between the operating and restraint quantities and then allows operation for a certain angle range and blocks operation for another angle range.For this specific relay, the angle is fixed at 110 °. No operation is possible if the angle between the operating and restraint quantities is greater than 110 °, irrespective of any other values of operating and restraint current magnitude. The stabilizing factor (k) is equal to 2 and is fixed. The relay provides further supervision by comparing the neutral current with the sum of the magnitudes of the three phase currents and the neutral current. The relay provides a settable pickup and slope and allows tripping above the characteristic.The relay has a minimum operating current of 5 percent of nominal current, or 0. 05 In. d) Produ ct D [9] The supplier markets this product as an â€Å"earth differential function† with an additional directional check. The relay, therefore, uses a typical biased differential earth-fault characteristic supervised by a directional element. The relay calculates the bias and differential current, where the differential current is the vector difference between the neutral current (measured by the neutral CT) and the residual current where Ir = Ia + Ib + Ic.The bias current is the highest of the three phase currents and the neutral current. The relay has a base sensitivity range of 5 percent (maximum sensitivity) to 50 percent (minimum sensitivity) for the differential current. This sensitivity value is valid from 0 to 1. 25 p. u. bias current. The bias characteristic has two slopes. The first slope is fixed at 70 percent, and the second is fixed at 100 percent. The first slope is valid from 1. 25 p. u. to a point corresponding to a 1 p. u. differential current. The second slo pe is valid beyond 1. 25 p. u.The directional element uses the neutral current as a reference because direction for this current is always the same for both in-zone and external faults. The relay compares the residual current with the neutral current in the vector plane. For an internal fault, the residual and neutral currents are out of phase. For an external fault, the residual and neutral currents are in phase. For the directional element, the relay compares the second harmonic current in the neutral CT with the fundamental component. If the second harmonic current is greater than a pre-set value, the REF element is disabled.This is a form of second harmonic blocking that provides additional security against operation during inrush but increased dependability during inzone faults. The relay has a minimum operating current of 5 percent of nominal current, or 0. 05 In. e) Product E [10] This relay calculates the differential current as Id = Ia + Ib + Ic + In and the residual curren t as Ir = Ia + Ib + Ic. Restraining current is the maximum of the positive-sequence, negativesequence, or zero-sequence current in the residual current. During external faults, the zero-sequence component of the residual current provides maximum restraint.The relay calculates the zero-sequence component as the amplitude of the vector difference between the neutral and residual current. During an external fault, the neutral and residual currents are in phase, so the resulting bias will be twice the neutral current. For an in-zone fault, the residual and neutral currents are out of phase so the restraint will be less than the neutral current. As previously stated, an external phase-to-phase fault can cause misoperation because of CT saturation. The negativesequence restraining quantity provides maximum restraint during such an external phase-to-phase fault.This relay uses a method where the level of restraint increases after a number of cycles. This method ensures the most sensitive r elay operation upon energization of a faulty transformer. When the restraint increases, security improves for external faults. The positive-sequence restraining quantity is intended to provide maximum restraint during symmetrical conditions such as three-phase faults and load. The relay uses a complicated algorithm to determine the value of the positive restraint component. Discussion of this algorithm is beyond the scope of this paper.The relay has a conventional bias characteristic with a pickup setting and slope setting. Both settings can be modified. 2) Setting Considerations for Maximum Sensitivity Some product-specific setting considerations have been discussed previously in this paper. Most relays have a minimum pickup level of 50 mA. Although all low-impedance REF relays this paper discusses have additional supervision for improved security, many manufacturers recommend a pickup setting greater than the steady-state neutral current resulting from load unbalance (quiescent ze ro-sequence current).This ensures that the relay picks up for actual faults, not for load unbalance. This practice reduces scheme sensitivity, because a greater operating current setting increases the minimum primary operating current. In cases where a biased earth differential protection is provided, the bias setting serves mainly to prevent the relay from operating for external faults resulting from CT saturation and other lesser important factors. These characteristics are fairly 8 fixed, and security against operation for external faults is almost guaranteed. IV.SENSITIVITY ISSUES This paper stated previously that relay sensitivity is not of great concern for faults on either solidly earthed star windings or impedance-earthed delta windings. There is always sufficient current to drive the operating element of the relay to ensure operation. Factors affecting REF scheme sensitivity are CT quality or specification, the magnetizing current the healthy phase CTs draw during a fault, the relay operating current, and the resistance earthing of the star-connected transformer. CT performance impacts greatly the sensitivity of the REF element.Lesser-quality CTs can make low-impedance REF protection more sensitive, because the operating voltage is lower and the CTs on the healthy phases draw less magnetizing current. Equation 6 provides relay sensitivity for both highimpedance and low-impedance REF, with slight variations between the two. The equation is valid for the high-impedance REF sensitivity calculation. In the case of low-impedance REF sensitivity, the varistor current is excluded and the relay does not have an operating voltage. Therefore, the magnetizing current is not the current the healthy phase CTs would draw at the operating voltage.A voltage equal to the sum of the lead and relay resistances multiplied by the fault current would appear across the healthy CTs. The magnetizing current of all CTs at this voltage should be added to the relay operating cur rent to determine the relay sensitivity. The lowimpedance REF measuring element will develop a much lower voltage across the healthy CTs and the magnetizing current necessary for those CTs will be substantially less than for the high-impedance REF case. Although the low-impedance REF relay minimum operating current is as much as 50 mA, the reduction in magnetizing current compensates for the greater pickup threshold.For example, assume that the CTs in a high-impedance REF scheme draw 15 mA magnetizing current at the operating voltage, and the relay operating current is 20 mA. It follows then that the total secondary current should be 4 †¢ 15 + 20 = 80 mA. The corresponding primary current must drive sufficient operating current through the relay to produce the magnetizing current necessary for the CTs to operate the relay. With a 200/1 CT ratio (impedance-earthed transformer), there is an implied minimum primary operating current of 16 A.For a typical 355 A NER, the only part o f the winding that is not covered, assuming zero fault resistance, is the bottom 16 / 355 †¢ 100 = 4. 5 percent. Taking the same example, assume that the CTs in a lowimpedance scheme draw only 2 mA magnetizing current because of the lower voltage across the CTs and the relay draws 50 mA. It follows then that the total secondary current should be 4 †¢ 2 + 50 = 58 mA. With the same CT ratio and NER as in the previous example, the minimum primary operating current is 11. 6 A. Clearly, the low-impedance REF function is more sensitive in this case. However, if the CTs used with the high- mpedance REF were of better quality and the magnetizing current were also 2 mA, the high-impedance REF relay would be more sensitive. In this case, (assuming zero fault resistance) the bottom 11. 6 / 355 †¢ 100 = 3. 3 percent of the winding is not covered. The transformer protection philosophy [11] of Eskom Distribution Division requires that the REF sensitivity for resistance-earthed star -connected windings be such that it can be set to pick up for faults between 10 percent and 25 percent of the maximum available earth-fault current for an earth fault on the transformer terminals.With this in mind, one can perform the necessary calculations to determine an adequate CT ratio and whether to apply high-impedance or low-impedance REF protection. As a general rule of thumb for high-impedance REF protection, the relay operating current should be greater than the sum of the CT magnetizing currents at the set voltage, i. e. , more fault current should be used to operate the relay than to magnetize the CTs on the healthy phases. This generally ensures greater stability. V. APPLICATION ASPECTS As we concluded previously, sensitivity becomes a concern only on resistance-earthed star windings.It is only in this case that the application of high-impedance vs. low-impedance REF protection must be considered. There are two important factors that may influence the decision. A. The Quality and Specification of the Available CTs Good-quality CTs with a very steep and linear magnetizing curve indicate CTs that require very little magnetizing current throughout most of the operating range. Poor-quality CTs require more magnetizing current. Perform calculations according to the specific CTs in use for a specific installation to determine the suitability of high-impedance vs. ow-impedance REF protection for the application. Perform this calculation as described under sensitivity issues. B. The Availability of Matching CT Ratios If the existing equipment is of such a nature that the same ratios are not available for both phase and neutral CTs, you should use low-impedance REF protection, because this type of protection can handle different CT ratios for phase and neutral CTs. However, if the same ratios are available for both phase and neutral CTs, further investigation should reveal whether high-impedance or low-impedance REF is the most suitable for the applicatio n.VI. CONCLUSIONS There is a general belief among many engineers that the fault current for faults close to the neutral point of a starconnected transformer is very small and insufficient to operate the REF protection. This is true only for resistance-earthed star-connected transformers. This paper makes no ruling on whether low-impedance or high-impedance REF protection is the better method, but it 9 provides the information and methods for choosing the more appropriate relay for a particular application.REF scheme sensitivity is a problem only on star windings with resistance earthing, because the fault current is a function of fault position, phase-to-neutral voltage, and earthing resistance value. For faults close to neutral, the fault current is very small. The relay operating current and CT magnetizing current are important in determining the winding coverage. In cases where there is always sufficient fault current to operate the REF relay, the choice between high-impedance an d low-impedance REF is not important.Issues such as available CT ratios for the phase and neutral CTs may dictate the choice. For poor-quality CTs that require larger magnetizing current than a better-quality CT at the same voltage, the lowimpedance REF element is more sensitive. Where you use good-quality CTs, however, the high-impedance REF relay is more sensitive. VII. ACKNOWLEDGEMENTS The authors wish to thank the following persons for their valuable contributions: Paul Gerber for his sensitivity calculations. Mike Everton for various discussions on the topic. Veronica van Zweel for the drawings.VIII. REFERENCES GEC Alsthom Measurements Limited, Protective Relays Application Guide, 3rd edition, 1990. [2] D. Robertson, ed. Power System Protection Reference Manual, Reyrolle Protection, Chapter 6, Stockfield: Oriel Press. [3] P. Bertrand, B. Gotzig, and C. Vollet, â€Å"Low Impedance Restricted Earth Fault Protection,† in Developments in Power System Protection, Conference P ublication No. 479, IEE, 2001. [4] SEL-387 Relay Training, Restricted Earth Fault Protection, Schweitzer Engineering Laboratories Inc. , Rev 0. 0, July 2001. [5] P. E.Sutherland, PE (SM), â€Å"Application of Transformer Ground Differential Protection Relays,† presented at the Industrial and Commercial Power Systems Technical Conference, Sparks, NV, 1999. [6] A. Guzman and L. S. Anderson, â€Å"Restricted Earth Fault Protection for Auto-Transformers Using a Directional Element. † Available at www. selinc. com [7] SEL-387-0, -5, -6 Instruction Manual, Current Differential Relay, Overcurrent Relay, Data Recorder, Schweitzer Engineering Laboratories, Date Code 20040628. [8] SIPROTEC, Differential Protection Manual, 7UT612, V4. , C53000– G1176–C148–1, Siemens. [9] Application Manual, ProtectIT Transformer Protection Terminal, RET521*2. 5, 1MRK 504 037-UEN, ABB. [10] T60 Transformer Management Relay, UR Series Instruction Manual, T60 Revision 4. 0x, Man ual P/N: 1601-0090-G1 (GEK-106490), GE Multilin, 2004 [11] P. A. Gerber, SCSAGAAG0 Rev 3, Transformer Protection Philosophy, Eskom Distribution Division, 2001. [12] Mini APPS Course (Analysis & Protection of Power Systems), vol 1, Section 9, Transformer Protection, 25 February to 1 March 1996. 1] Protection Field Engineer. He is currently a Chief Engineer: Protection Specialist in Resources and Strategy, a Corporate Division of Eskom Holdings Limited. He is responsible for Distribution Division National Contracts for protection schemes and equipment, general protection technology direction setting and technology management, and the implementation of Distribution Automation and Substation Automation in Eskom’s Distribution Division.He has authored a number of protection and substation automation related papers. He is a Registered Professional Engineer in South Africa. Casper Labuschagne earned his Diploma (1981) and Masters Diploma (1991) in Electrical Engineering from Vaal Tr iangle Technicon, South Africa. After gaining 20 years of experience with the South African utility Eskom, where he served as Senior Advisor in the protection design department, he began work at SEL in 1999 as a Product Engineer in the Substation Equipment Engineering group.Presently, he is Lead Engineer in the Research and Development group. He is registered as a Professional Technologist with ECSA, the Engineering Counsel of South Africa, and has authored and coauthored several technical papers. IX. BIOGRAPHIES Izak van der Merwe obtained his B. Eng (Electrical) degree from the University of Stellenbosch in 1991. He started to work for Eskom in 1993 as a  © 2005, 2007 by Eskom Enterprises and Schweitzer Engineering Laboratories, Inc. All rights reserved. 20070711 †¢ TP6207-01