Explosions may occur in the equipments which have insulating oil, particularly during short circuits. This may result in fire and hazardous conditions to personnel and equipments

Individual generators with reduced voltage in a power station or a group of generators operating at low voltage may lead to loss of synchronism, subsequently resulting in islanding. The purpose of an Electric Power System is to generate and supply electrical energy to consumers. The power system should be designed and managed to deliver this energy to the utilization points with both reliability and economically The capital investment involved in power system for the generation, transmission and distribution is so great that the proper precautions must be taken to ensure that the equipment not only operates as nearly as possible to peak efficiency, but also must be protected from accidents The normal path of the electric current is from the power source through copper (or aluminium) conductors in generators, transformers and transmission lines to the load and it is confined to this path by insulation. The insulation, however, may break down, either by the effect of temperature and age or by a physical accident, so that the current then follows abnormal path an generally known as Short Circuit or Fault If signal is generated from single sensor or source it is called as single channel signal. If the signals are generated from multiple sensors or multiple sources or multiple signals are generated from same source called as Multi channel signal. Example ECG signals. Multi channel signal will be the vector sum of signals generated from multiple sources. Conformance Meeting specifications or industry standards. How far the products physical and performance characteristic match with the set standards is called conformity.

4. Reliability - Consistency of performance over time, average time for the unit to fail. Under prescribed conditions of use of the product the probability of surviving over a specified period is termed as reliability of that product.

5. Durability - Useful life includes repair. The quantum of use a customer gets from a product before it wears out beyond further use or when a replacement is essential is called durability.

Depending upon the needs of the customers any product has to be supplied by the manufacturer. However the product should have certain characteristics and features. Customers only determine ultimately whether the product has been of expected quality. Various dimensions of quality that the customers do look for in a product, in order to satisfy their needs, only decide the characteristics of a product. For a manufactured product the dimensions of Quality are as following:

1. Performance Primary product characteristics such as the brightness of the picture. This is the deciding driving force deciding the operating characteristics.

2. Features Secondary characteristics, added 1 features, such as remote control. Though this attribute is a secondary characteristic, it necessarily supplements the basic functioning of the product.

TQM works effectively if the organization works in a family manner. Here management is like a father, employees are the children and manager is like mother and as father and mother takes care for their home collectively the same way, management and managers are supposed to take care for their organization with the help of tool called TQM. Total quality management is called total because entire organization is involved, Quality means degree of excellence. And management in literal sense means getting things done by others. In a TQM effort, all members of an organization participate in improving processes, products, services and the culture in which they work. The earlier introduced quality management concept is now taken over by Total quality management. To have effective TQM the first requirement is strong internal motivation and emotional involvement for implementation.

Total quality management is a management's approach towards the quality, it can be in regard to products, customer satisfaction and employees satisfaction. The concept of TQM was developed by an American W. Edwards Deming and i.e. why it is called as Deming's concept of TQM .He introduced this concept for improving the quality of various products and services. Earlier it was just related with the quality of products which a organization is producing but now other concepts like marketing, finance design, customer service has also joined the area. Which means that now good numbers of things are there to manage. TQM works on one belief that mistakes can be avoided and defects can be prevented. And management should believe in watching each and every step.

Silicon steel (Iron + 0.3 to 4.5% silicon) in the laminated form. Addition of silicon in proper percentage eliminates ageing & reduce core loss. Low silicon content steel or dynamo grade steel is used in rotating electrical machines and are operated at high flux density. High content silicon steel (4 to 5% silicon) or transformer grade steel (or high resistance steel) is used in transformers. Further sheet steel may be hot or cold rolled. Cold rolled grain oriented steel (CRGOS) is costlier and superior to hot rolled. CRGO steel is generally used in transformers.

For the same resistance and length, cross sectional area of aluminum is 61% larger than that of the copper conductor and almost 50% lighter than copper. Though the aluminum reduces the cost of small capacity transformers, it increases the size and cost of large capacity transformers. Aluminum is being much used now a day's only because copper is expensive and not easily available. Aluminum is almost 50% cheaper than Copper and not much superior to copper.

A strike impacting the structure of interest or the soil (or objects) within a few meters from the structure of interest. Energy Deposition: The time integral of the power dissipated in a clamping-type surge protective device during a current surge of a specified waveform. Failure Mode: The process and consequences of device failure.

Leakage Current: Any current, including capacitive coupled currents, that can be conveyed from accessible parts of a product to ground or to other accessible parts of the product.

Lightning Protection System (LPS): The complete system used to protect a space against the effects of lightning. It consists of both external and internal lightning protection systems.

Temporary over voltages represent a threat to equipment as well as to any surge protective devices that may have been provided for the mitigation of surges. The scope of this Guide includes temporary over voltages only as a threat to the survival of SPDs, and therefore includes considerations on the selection of suitable SPDs. No equipment performance requirements are specified in this Guide. What is recommended is a rational, deliberate approach to recognizing the variables that need to be considered simultaneously, using the information presented here to define a set of representative situations. For specific applications, the designer has to take into consideration not only the rates of occurrence and the waveforms described in this Guide, but also the specific power system environment and the characteristics of the equipment in need of protection. As an example, the following considerations are necessary to reach the goal of practical surge immunity. Manufacturing organization generally transfer tangible inputs or raw materials into some tangible output (ex: steel, refrigerator, toothpaste, soap etc.) Other inputs such as labour skills. management skills, capitals are used as well. The 5^ prime h distinction is based on lead time/response time to customers demand. Manufacturers take generally some lead time (i.e. time period from placing the order to get the product) in terms of days/week. Whereas the services are offered within few minutes of customers arrival. For ex: ATM Service, getting postal stamps, getting grocery from a retail shop and getting examined by a doctor etc. The 6 ^ (ih) distinction is on availability. Products can be available from regional, national or international markets due to availability of transportations and distribution facilities whereas, service can't shipped to distant locations. Thus service organization requiring direct customer contact must locate very near to the customers. The 7th distinction is based on liabilities/facilities. Manufacturing unit/organization producing products generally require larger facilities, more automation and greater capital investment than service providing organization. The 8th distinction s based on capital/labour priority. Generally manufacturing firm producing goods/products require more capital than a service provider. Ex. An automobile firm requires more capital than a post office/Nursing home. The 9 ^ (th) and 10 ^ (sh) distinction is based on quality and demand variation. The United Nations Conference on Environment and Development held in Rio de Janerio in 1992 and popularly known as Earth summit followed by the world summit on sustainable Development in 2002, have highlighted key issues of global environmental concern. Environmental pollution cannot be removed by laws alone. The proper implementation and especially public participation are important aspects. Public participation is possible only when the public is aware about the ecological and environmental issues. Lime stone and clay are ground to fine powder separately and are mixed together Water is added to make a thick paste which contains 14% of moisture. The paste format are dried and off charged into a rotary kiln. The product obtained often calcinations in rotary kiln. The linker I obtained as a result of incipient fusion and sintering at a temp about 1400?c to 1500? c. The linker is cooled to preserve the meta stable compounds and there solid solutions Dispersion of one solid with another solid which made the clinker again heated Clinker is again cooled and grounded in tube mills where 2-3% gypsum is added. The purpose of adding gypsum is to coat the cement particle by interfering the process of hydration of cement particles. The crushed raw materials are fed in to a ball mill and a little water is added. The steel balls in the ball mill pulverized the Ferranti surge absorber: Ferranti surge absorber consists of an air core inductor which is connected in series with the line and surrounded by an earth metallic sheet. The earth metallic sheet is known as dissipater, The dissipater is insulated from the inductor by the air as shown in Figure. This surge absorber acts like an air-cored transformer whose primary is the low inductance inductor and the dissipater as the single-turn short circuit secondary. Whenever a travelling wave is incident on the surge absorber, energy is transformed by mutual inductance between the coil and dissipatcr. Because of the series inductance the steepness of the wave is also reduced. The arc caused between the faulty conductor and the ground gets extinguished and restarts many times, this repeated initiation and extinction of the arc across the fault produces severe voltage oscillations of the order of nearly three to four times the nominal voltage. Arcing Grounds is a phenomenon which is observed in ungrounded three phase systems. In ungrounded three phase systems operating in a healthy balanced conditions, capacitances are formed between the conductors and ground. The voltage across these capacitances is the phase voltage. Now, in the event of a ground fault, the voltage across the faulty conductor becomes zero while the voltages across the healthy conductors increase by a factor of 1.732. The functions of a lightning arrester or surge dividers can be listed as below.

1. Under normal voltage level, these devices withstand easily the system voltage as electrical insulator and provide no conducting path to the system current.

2. On occurrence of voltage surge in the system, these devices provide very low impedance path for the excess charge of the surge to the ground.

3. After conducting the charges of surge, to the ground, the voltage becomes to its normal level. Then lightning arrester regains its insulation properly and prevents regains its insulation property and prevents further conduction of current, to the ground. The previously discussed two methods, i.e. earthing screen and over-head earth wire are very suitable for protecting an electrical power system from directed lightning strokes but system from directed lightning strokes but these methods can not provide any protection against high voltage travelling wave which may propagate through the line to the equipment of the sub-station.

The lightning arrester is a devices which provides very low impedance path to the ground for high voltage travelling waves.

The concept of a lightning arrester is very simple. This device behaves like a nonlinear electrical resistance. The resistance decreases as voltage increases and vice-versa, after a certain level of voltage. This method of over voltage protection is similar as earthing screen. The only difference is, an earthing screen is placed over an electrical sub-station, whereas, overhead earthwire is placed over electrical transmission network. One or two stranded GI wires of suitable cross-section are placed over the transmission conductors. These GI wires are properly grounded at each transmission tower. These overhead ground wires or earthwire divert all the lightning strokes to the ground instead of allowing them to strike directly on the transmission conductors. When a no load transmission line is suddenly switched on, the voltage on the line becomes twice of normal system voltage. This voltage is transient in nature. When a loaded line is suddenly switched off or interrupted, voltage across the line also becomes high enough current chopping in the system mainly during opening operation of air blast circuit breaker, causes over voltage in the system. During insulation failure, a live conductor is suddenly earthed. This may also caused sudden over voltage in the system. If emf wave produced by alternator is distorted, the trouble of resonance may occur due to 5th or higher harmonics. Actually for frequencies of 5th or higher harmonics, a critical situation in the system so appears, that inductive reactance of the system becomes just equal to capacitive reactance of the system. As these both reactance cancel each other the system becomes purely resistive. This phenomenon is called resonance and at resonance the system voltage may be increased enough.

The over voltage stresses applied upon the power system, are generally transient in nature. Transient voltage or voltage surge is defined as sudden sizing of voltage to a high peak in very short duration. The voltage surges are transient in nature, that means they exist for very short duration. The main cause of these voltage surges in power system are due to lightning impulses and switching impulses of the system. But over voltage in the power system may also be caused by, insulation failure, arcing ground and resonance etc.

The voltage surges appear in the electrical system due to switching surge, insulation failure, arcing ground and resonance are not very large in magnitude. These over voltages hardly cross the twice of the normal voltage level. Generally, proper insulation to the different equipment of power system is sufficient to prevent any damage due to these over voltages. But over voltages occur in the power system due to lightning is very high. If over voltage protection is not provided to the power system, there may be high chance of severe damage. There are always a chance of suffering an electrical power system from abnormal over voltages. These abnormal over voltages may be caused due to various reason such as, sudden interruption of heavy load, lightening impulses, switching impulses etc. These over voltage stresses may damage insulation of various equipments and insulators of the power system. Although, all the over voltage stresses are not strong enough to damage insulation of system, but still these over voltages also to be avoided to ensure the smooth operation of electrical power system. It is economically unviable to have a 100% protection of the entire system in concern. Therefore, the cost of the designed protection system varies with the criticality and importance of the protected zone. The protection system for more critical portions

is generally costly, as all the features of a good protection system is maximized here. But a small motor can be protected by a simple thermally operated relay, which is simple and cheap. Therefore, the cost of the protection system should be adequate in its cost. 1.4.7 Some basic terminologies used in protection system Some basic terminologies commonly used in the protection system are enlisted below. i) Measuring Relay ii) Fault Clearing Time iii) Auxilliary relay iv) Relay Time v) Pick up value vi) Reset Value vii) Drop out viii) Reach (under and over reaches) ix) Relay Burden x) Unit/ Non unit protection xi) All or Nothing relay.

Question :

Explain the typical causes of computer failures.