WIND TURBINE

    A wind turbine is a machine that converts the wind's kinetic energy into rotary mechanical energy, which is then used to do work. In more advanced models, the rotational energy is converted into electricity, the most versatile form of energy, by using a generator.

   For thousands of years people have used windmills to pump water or grind grain. Even into the twentieth century tall, slender, multi-vaned wind turbines made entirely of metal were used in American homes and ranches to pump water into the house's plumbing system or into the cattle's watering trough. After World War I, work was begun to develop wind turbines that could produce electricity. Marcellus Jacobs invented a prototype in 1927 that could provide power for a radio and a few lamps but little else. When demand for electricity increased later, Jacobs's small, inadequate wind turbines fell out of use.

  The first large-scale wind turbine built in the United States was conceived by Palmer Cosslett Putnam in 1934; he completed it in 1941. The machine was huge. The tower was 36.6 yards (33.5 meters) high, and its two stainless steel blades had diameters of 58 yards (53 meters). Putnam's wind turbine could produce 1,250 kilowatts of electricity, or enough to meet the needs of a small town. It was, however, abandoned in 1945 because of mechanical failure.

    With the 1970s oil embargo, the United States began once more to consider the feasibility of producing cheap electricity from wind turbines. In 1975 the prototype Mod-O was in operation. This was a 100 kilowatt turbine with two 21-yard (19-meter) blades. More prototypes followed (Mod-OA, Mod-1, Mod-2, etc.), each larger and more powerful than the one before. Currently, the United States Department of Energy is aiming to go beyond 3,200 kilowatts per machine.

   Many different models of wind turbines exist, the most striking being the vertical-axis Darrieus, which is shaped like an egg beater. The model most supported by commercial manufacturers, however, is a horizontal-axis turbine, with a capacity of around 100 kilowatts and three blades not more than 33 yards (30 meters) in length. Wind turbines with three blades spin more smoothly and are easier to balance than those with two blades. Also, while larger wind turbines produce more energy, the smaller models are less likely to undergo major mechanical failure, and thus are more economical to maintain.

     Wind farms have sprung up all over the United States, most notably in California. Wind farms are huge arrays of wind turbines set in areas of favorable wind production. The great number of interconnected wind turbines is necessary in order to produce enough electricity to meet the needs of a sizable population. Currently, 17,000 wind turbines on wind farms owned by several wind energy companies produce 3.7 billion kilowatt-hours of electricity annually, enough to meet the energy needs of 500,000 homes.

      A wind turbine consists of three basic parts: the tower, the nacelle, and the rotor blades. The tower is either a steel lattice tower similar to electrical towers or a steel tubular tower with an inside ladder to the nacelle. Most towers do not have guys, which are cables used for support, and most are made of steel that has been coated with a zinc alloy for protection, though some are painted instead. The tower of a typical American-made turbine is approximately 80 feet tall and weighs about 19,000 pounds.

      The nacelle is a strong, hollow shell that contains the inner workings of the wind turbine. Usually made of fiberglass, the nacelle contains the main drive shaft and the gearbox. It also contains the blade pitch control, a hydraulic system that controls the angle of the blades, and the yaw drive, which controls the position of the turbine relative to the wind. The generator and electronic controls are standard equipment whose main components are steel and copper. A typical nacelle for a current turbine weighs approximately 22,000 pounds.

    The most diverse use of materials and the most experimentation with new materials occur with the blades. Although the most dominant material used for the blades in commercial wind turbines is fiberglass with a hollow core, other materials in use include lightweight woods and aluminum. Wooden blades are solid, but most blades consist of a skin surrounding a core that is either hollow or filled with a lightweight substance such as plastic foam or honeycomb, or balsa wood. A typical fiberglass blade is about 15 meters in length and weighs approximately 2,500 pounds.

     Wind turbines also include a utility box, which converts the wind energy into electricity and which is located at the base of the tower. Various cables connect the utility box to the nacelle, while others connect the whole turbine to nearby turbines and to a transformer.

The Manufacturing  Process

    Before consideration can be given to the construction of individual wind turbines, manufacturers must determine a proper area for the siting of wind farms. Winds must be consistent, and their speed must be regularly over 15.5 miles per hour (25 kilometers per hour). If the winds are stronger during certain seasons, it is preferred that they be greatest during periods of maximum electricity use. In California's Altamont Pass, for instance, site of the world's largest wind farm, wind speed peaks in the summer when demand is high. In some areas of New England where wind farms are being considered, winds are strongest in the winter, when the need for heating increases the consumption of electrical power. Wind farms work best in open areas of slightly rolling land surrounded by mountains. These areas are preferred because the wind turbines can be placed on ridges and remain unobstructed by trees and buildings, and the mountains concentrate the air flow, creating a natural wind tunnel of stronger, faster winds. Wind farms must also be placed near utility lines to facilitate the transfer of the electricity to the local power plant.

Preparing the site

     Wherever a wind farm is to be built, the roads are cut to make way for transporting parts. At each wind turbine location, the land is graded and the pad area is leveled. A concrete foundation is then laid into the ground, followed by the installation of the underground cables. These cables connect the wind turbines to each other in series, and also connect all of them to the remote control center, where the wind farm is monitored and the electricity is sent to the power company.

Erecting the tower

    Although the tower's steel parts are manufactured off site in a factory, they are usually assembled on site. The parts are bolted together before erection, and the tower is kept horizontal until placement. A crane lifts the tower into position, all bolts are tightened, and stability is tested upon completion.

Nacelle

    The fiberglass nacelle, like the tower, is manufactured off site in a factory. Unlike the tower, however, it is also put together in the factory. Its inner workings—main drive shaft, gearbox, and blade pitch and yaw controls—are assembled and then mounted onto a base frame. The nacelle is then bolted around the equipment. At the site, the nacelle is lifted onto the completed tower and bolted into place.

Rotary blades

    Aluminum blades are created by bolting sheets of aluminum together, while wooden blades are carved to form an aerodynamic propeller similar in cross-section to an airplane wing.

By far the greatest number of blades, however, are formed from fiberglass. The manufacture of fiberglass is a painstaking operation. First, a mold that is in two halves like a clam shell, yet shaped like a blade, is prepared. Next, a fiberglass-resin composite mixture is applied to the inner surfaces of the mold, which is then closed. The fiberglass mixture must then dry for several hours; while it does, an air-filled bladder within the mold helps the blade keep its shape. After the fiberglass is dry, the mold is then opened and the bladder is removed. Final preparation of the blade involves cleaning, sanding, sealing the two halves, and painting.

The blades are usually bolted onto the nacelle after it has been placed onto the tower. Because assembly is easier to accomplish on the ground, occasionally a three-pronged blade has two blades bolted onto the nacelle before it is lifted, and the third blade is bolted on after the nacelle is in place.

Installation of control systems

     The utility box for each wind turbine and the electrical communication system for the wind farm is installed simultaneously with the placement of the nacelle and blades. Cables run from the nacelle to the utility box and from the utility box to the remote control center.

Quality Control

     Unlike most manufacturing processes, production of wind turbines involves very little concern with quality control. Because mass production of wind turbines is fairly new, no standards have been set. Efforts are now being made in this area on the part of both the government and manufacturers.

    While wind turbines on duty are counted on to work 90 percent of the time, many structural flaws are still encountered, particularly with the blades. Cracks sometimes appear soon after manufacture. Mechanical failure because of alignment and assembly errors is common. Electrical sensors frequently fail because of power surges. Non-hydraulic brakes tend to be reliable, but hydraulic braking systems often cause problems. Plans are being developed to use existing technology to solve these difficulties.

  Wind turbines do have regular maintenance schedules in order to minimize failure. Every three months they undergo inspection, and every six months a major maintenance checkup is scheduled. This usually involves lubricating the moving parts and checking the oil level in the gearbox. It is also possible for a worker to test the electrical system on site and note any problems with the generator or hookups.

Environmental Benefits and Drawbacks

     A wind turbine that produces electricity from inexhaustible winds creates no pollution. By comparison, coal, oil, and natural gas produce one to two pounds of carbon dioxide (an emission that contributes to the greenhouse effect and global warming) per kilowatt-hour produced. When wind energy is used for electrical needs, dependence on fossil fuels for this purpose is reduced. The current annual production of electricity by wind turbines (3.7 billion kilowatt-hours) is equivalent to four million barrels of oil or one million tons of coal.

     Wind turbines are not completely free of environmental drawbacks. Many people consider them to be unaesthetic, especially when huge wind farms are built near pristine wilderness areas. Bird kills have been documented, and the whirring blades do produce quite a bit of noise. Efforts to reduce these effects include selecting sites that do not coincide with wilderness areas or bird migration routes and researching ways to reduce noise.

The Future

    The future can only get better for wind turbines. The potential for wind energy is largely untapped. The United States Department of Energy estimates that ten times the amount of electricity currently being produced can be achieved by 1995. By 2005, seventy times current production is possible. If this is accomplished, wind turbines would account for 10 percent of the United States' electricity production.

      Research is now being done to increase the knowledge of wind resources. This involves the testing of more and more areas for the possibility of placing wind farms where the wind is reliable and strong. Plans are in effect to increase the life span of the machine from five years to 20 to 30 years, improve the efficiency of the blades, provide better controls, develop drive trains that last longer, and allow for better surge protection and grounding. The United States Department of Energy has recently set up a schedule to implement the latest research in order to build wind turbines with a higher efficiency rating than is now possible. (The efficiency of an ideal wind turbine is 59.3 percent. That is, 59.3 percent of the wind's energy can be captured. Turbines in actual use are about 30 percent efficient.) The United States Department of Energy has also contracted with three corporations to research ways to reduce mechanical failure. This project began in the spring of 1992 and will extend to the end of the century.

    Wind turbines will become more prevalent in upcoming years. The largest manufacturer of wind turbines in the world, U.S. Windpower, plans to expand from 420 megawatt capacity (4,200 machines) to 800 megawatts (8,000 machines) by 1995. They plan to have 2,000 megawatts (20,000 machines) by the year 2000. Other wind turbine manufacturers also plan to increase the numbers produced. International committees composed of several industrialized nations have formed to discuss the potential of wind turbines. Efforts are also being made to provide developing countries with small wind turbines similar to those Marcellus Jacobs built in the 1920s. Denmark, which already produces 70 percent to 80 percent of Europe's wind power, is developing plans to expand manufacture of wind turbines. The turn of the century should see wind turbines that are properly placed, efficient, durable, and numerous. 

ELECTRICAL GENERATOR

In electricity generation, an electrical generator is a device that converts kinetic energy to electrical energy, generally using electromagnetic induction. The reverse conversion of electrical energy into mechanical energy is done by a motor, and motors and generators have many similarities. The source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, or any other source of mechanical energy.

Dynamo

    The Dynamo was the first electrical generator capable of delivering power for industry. The dynamo uses electromagnetic principles to convert mechanical rotation into a pulsing direct electric current through the use of a commutator. A dynamo machine consists of a stationary structure, which provides a constant magnetic field, and a set of rotating windings which turn within that field. On small machines the constant magnetic field may be provided by one or more permanent magnets; larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called field coils.

   The first dynamo based on Faraday's principles was built in 1832 by Hippolyte Pixii, a French instrument maker. It used a permanent magnet which was rotated by a crank. The spinning magnet was positioned so that its north and south poles passed by a piece of iron wrapped with wire. Pixii found that the spinning magnet produced a pulse of current in the wire each time a pole passed the coil. Furthermore, the north and south poles of the magnet induced currents in opposite directions. By adding a commutator, Pixii was able to convert the alternating current to direct current.

    Unlike the Faraday disc, many turns of wire connected in series can be used in the moving windings of a dynamo. This allows the terminal voltage of the machine to be higher than a disc can produce, so that electrical energy can be delivered at a convenient voltage.

    The relationship between mechanical rotation and electric current in a dynamo is reversible; the principles of the electric motor were discovered when it was found that one dynamo could cause a second interconnected dynamo to rotate if current was fed through it.

   The transformative ability of a dynamo to change energy from electrical power to mechanical power and back again could be exploited as a current-compensation and balancing device to even out power distribution on interconnected, unbalanced circuits.

Concepts

     The generator moves an electric current, but does not create electric charge, which is already present in the conductive wire of its windings. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside. Other types of electrical generators exist, based on other electrical phenomena such as piezoelectricity, and magnetohydrodynamics. The construction of a dynamo is similar to that of an electric motor, and all common types of dynamos could work as motors.

Excitation

    A generator that uses field coils instead of permanent magnets requires a current flow to be present in the field coils for the generator to be able to produce any power at all. If the field coils are not powered, the rotor can spin without the generator producing any usable electrical energy.

    For older and very large power generating equipment, it has been traditionally necessary for a small separate exciter generator to be operated in conjunction with the main power generator. This is a small permanent-magnet generator which produces the constant current flow necessary for the larger generator to function.

    Most modern generators with field coils feature a capability known as self-excitation where some of the power output from the rotor is diverted to power the field coils. Additionally the rotor or stator contains a small amount of magnetizable metal, which retains a very weak residual magnetism when the generator is turned off. The generator is turned on with no load connected, and the initial weak field creates a weak flow in the field coils, which in turn begins to slightly affect the rotor to begin to produce current that then further strengthens the field. This feedback loop continues to increase field voltage and output power until the generator reaches its full operating output level.

    This initial self-excitation feedback process does not work if the generator is started connected to a load, as the load will quickly dissipate the slight power production of the initial field buildup process.

   It is additionally possible for a self-exciting generator either turned off or started with a load connected to result in dissipation of the residual magnetic field, resulting in complete non-function of the generator. In the case of a 220v portable generator commonly used by consumers and construction contractors, this loss of the residual field can usually be remedied by shutting down the generator, disconnecting all loads, and connecting what are normally the high-voltage/amperage generator outputs to the terminals of a common 9-volt battery. This very small current flow from the battery (in comparison with normal generator output) is enough to restore the residual self-exciting magnetic field. Usually only a moment of current flow, just briefly touching across the battery terminals, is enough to restore the field.

Terminology

    The parts of a dynamo or related equipment can be expressed in either mechanical terms or electrical terms. Although distinctly separate, these two sets of terminology are frequently used interchangeably or in combinations that include one mechanical term and one electrical term. This causes great confusion when working with compound machines such as a brushless alternator or when conversing with people who work on a machine that is configured differently than the machines that the speaker is used to.

Mechanical

 Rotor: The rotating part of an alternator, generator, dynamo or motor.

  Stator: The stationary part of an alternator, generator, dynamo or motor.

Electrical

  Armature: The power-producing component of an alternator, generator, dynamo or motor. The armature can be on either the rotor or the stator.

  Field: The magnetic field component of an alternator, generator, dynamo or motor. The magnetic field of the dynamo or alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator. 

Modular Power Converter for Railways

    power System Technology designs and manufactures custom power solutions for the medical, transportation and defence industries. To prevent the risks associated with discrete solutions, Power System Technology uses Vicor's wide range of field-proven high-density power modules.

       Working in partnership with Vicor, Power System Technology designs and manufactures custom and standard modular power converters dedicated to railway applications. Using their expertise in EMI, thermal management, mechanical packaging and environmental qualifications, our engineers add extra circuitry and intelligence to standard Vicor power modules.

EURO CASSETTE POWER CONVERTERS

    Specially designed for the hard environment of the railway, the PST00 and PST15 Eurocard families comply with EN50155 standards for transients and EMI. The integration of Vicor power modules provides very high reliability, high power density and the ability to configure each output voltage from 1VDC to 95VDC.

  The pin-outs are compatible with most products available on the market, and options like very low profile, extended temperature range or N+1 redundancy are available.

FULL CUSTOM OR SEMI-STANDARD RAILWAY POWER CONVERTERS

    Power System Technology has designed a wide range of full custom or semi-standard products dedicated to railway systems. Our range includes DC/DC converters for the front light of the train, embedded electronic supplies and video entertainment. Our expertise and experience in design, combined with the benefits of Vicor DC/DC power modules, ensure very short time-to-market, minimum engineering costs and high power density solutions.

PCB / DIN RAIL MOUNTING

       Power System Technology's PCB / din rail mounting solutions provide plug-and-play solutions that are easy to implement into customers' systems. These solutions come with a warranty that the appropriate protections have been taken into account to meet various railway standards.

     With a variety of input voltage and output voltage ranges, and different sizes and formats, these standard solutions will be the perfect answer for critical time-to-market applications.

CHASSIS MOUNTING / CONDUCTION COOLED POWER CONVERTERS

       With ambient temperature at 70°C and no air forced in railway applications, conduction-cooled products from Power System Technology are the ideal solution for 'hermetic' electronic equipment. The heat is spread to the exterior by mounting the base plate of the DC/DC or AC/DC converter to the chassis, thus avoiding a rise in internal temperature. The removal of the heat sink aluminium of the converter also saves weight.

EXPERT SYSTEMS

Expert System

     “an expert system is a computer program that represents and reason s with knowledge of a specialized subject with a view to solving problems directly or giving advice”.

Advantages of Expert System

    Expert system works by storing expertise of a domain expert. Then a user can interact with the system and let it solve a problem using the same logic generally used by the expert. Usually the expert systems is faster and more accurate than a human , and does not get tired or bored. A very strong benefit of Expert Systems is being able to widely distribute the knowledge of a single expert , or being able to accumulate in one place the knowledge of several widely represented experts. Some situations when ES should be considered Only one expert is available , but is needed in multiple locations. Expertise is divided among several experts. Expertise is required is a harsh environment.

An expert is retiring. Expert systems are especially helpful when a task is performed only occasionally and the expert has to relearn the procedure each time it is performed . one can use expert systems are especially helpful when a task is performed only occasionally and the expert has to relearn the procedure each time it is performed. One can use Expert systems to standardize operations . another use for expert system is as job aid for experts. This will allow them to perform more accurately, more consistently, and faster , freeing up time for the expert to be more creative in performing the task. This is especially helpful when dealing with tedious, repetitious tsks. Thus an expert system is needed to

completely fulfill a function that normally requires a human expertise or it may play the role of an assistant to a human decision maker. An expert system can be distinguished from a more conventional application program in that:

     It simulates human reasoning about a problem domain, rather than simulate the domain it self.

      It performs reasoning over representations of human knowledge, in addition to doing numerical calculations or data retrieval.

    It solves problems by heuristic or approximate methods, which unlike algorithmic solutions are not guaranteed to succeed.

   Traditional program is termed as procedure oriented programming where as for an expert system term it as object – oriented programming.

SOLAR POWER SYSTEM

     Can you ever imagine life without lights, fans, cars, computers and television or of fetching water from the well and river? This is what life would have been like had man not discovered the uses of energy both renewable and nonrenewable resources.are of different types for e.g. solar energy, wind energy, tidal energy, geothermal energy etc. Now let us focus on solar energy as it is one of the abundant forms of energy available. Power "For the successful technology, reality must take precedence over public relations, for nature cannot be fooled." Richard Feyman Energy. It has been already said that the rationale for going into space, apart from the fact that the human race must extend its limits and explore and then conquer space, has to do with retrieving energy, mainly the Sun's energy. About 80 % of the total energy demanded by our society is supplied from fossil fuels. 90% of the CO2 which is the major cause of the greenhouse effect comes from combustion. It is now widely accepted that the only way to reduce the environmental risks while sustaining the economic growth is to develop a large-scale alternative energy system which is ecologically benign.

     A scientific venture must be pursued when it follows certain logic and the solution is correct, even if technology for proper utilization is not current or not available. Such is this case. Although the human race would perhaps not be able in the very immediate future to exploit the untapped potential of solar energy, it is certainly a direction that must be

followed. Exclusive dependence on fossil fuels will inevitably lead to energy shortages. 

    It must be remembered that this scheme was one of the main determinants in choosing the location of the space colony. The liberationpoints along the Earth's path were chosen primarily for their constant exposure to sunshine Solar Energy here on Earth Why should we go into space to get solar energy and not profit directly from it here on Earth? The answer is twofold.

Solar Power Satellites:

   A possible scheme for producing power on a large scale contemplates placing giant solar modules alongside the colony where energy generated from sunlight would be converted to microwaves and beamed to antennas on earth for recon version to electric power. On ground, the microwave power is rectified and converted to the commercial electric power.

      To produce as much power as five large nuclear power plants (1 billion watts each) several square km of solar collectors, weighing more than 5 million kg would have to be assembled in the settlement. An earth-based antenna 5 miles in diameter would be required for reception. These vast assemblies are often referred to as Solar Power Satellites (SPS) .The concept of the SPS is revolutionary with a high potentiality to solve the global environmental problems, as it uses the limitless solar energy, it utilizes the space outside of the earth ecology system, and it has no by-product waste. The use of Even though one of its panels could never be deployed, Skylab effectively demonstrated solar energy.A large-scale receiving antenna, retina, is necessary to collect the microwave power from space.

The Atmosphere :

     The benign atmosphere protects us from the intensity of the sun's rays, that are filtered by our gaseous cover. That same protective effect which shields us and allows life on Earth also prevent us from fully receiving the Sun's energy. It is estimated that, in average, between 0.1 and 0.2 kW/m2 of solar energy can be received from the Sun on the Earth's surface. In near Earth space the quantity o energy that can be collected is approximately ten times as much, that is, around 1 to 2 kW/m2 in average. This first reason is obviously decisive. 

The Earth's rotation :

       But even if extra sensitive solar panels could be engineered, there is another problematic factor that complicates full utilization of the sun's energy. The rotation of the Earth, as we very well know, gives rise to days and nights, which means that during 12 hours in average no sunlight hits the surface of our planet. Because of this, solar energy devices have to trap the heat during the night period and great pains are taken to ensure that minimum heat gets lost. None of these problems will be met in space, where sunshine is constant and with far greater intensity

CONTROL OF SINGLE PHASEVOLTAGE CONVERTERS

In most power electronic applications, the power input is of 50 or 60 hertz AC voltage provided by the electric utility. It further converted to a DC voltage for various applications. The inexpensive rectifiers with diodes convert AC to DC and the output voltage is uncontrolled. The controlled rectifiers are used for providing variable/ constant output voltage. The dc output voltage of a controlled/uncontrolled rectifier should be ripple free. Therefore a large capacitor is connected as a filter on dc side. Due to this, controlled/uncontrolled rectifier has the following drawbacks; these rectifiers draw highly distorted current from the Utility and Power factor is very low. To take the edge off these drawbacks, High performance rectifiers are proposed in this paper. One of the authors has proposed a digital controller-based predictive instantaneous current control scheme for the single-phase voltage-fed rectifier and its modified analogue version. Although the control schemes obtain a sufficient performance, further simplification is necessary to realize an economical PFC converter system in practice. In this paper propose a simplified analogue controller-based predictive instantaneous current control scheme for single-phase voltage fed PFC converters, which is obtained from further modification of the original digital scheme. Since three phase converters have phase interference, a particular arrangement of the controller modulator for the three phase system is employed to avoid such phase interference. As a result, a simple predictive instantaneous current control scheme for three-phase voltage-fed PFC converters is obtained. In this paper, the predictive control methods for PFC are reviewed and their system configuration is highlighted in section II. The principles of the predictive control algorithm are discussed in same section. . In section III, the simulation results are presented. The conclusion is drawn in the last section.

CONFIGURATIONS:

A. Classification of different Topology

    Improved power quality converters are classified on the basis of topology and type of converter used. The topology-based classification is categorized on the basis of boost, buck, buck–boost, multilevel, unidirectional and bidirectional voltage, current, and power flow. The converter type can be step-up and step-down choppers, voltage source and current-source inverters, bridge structure, etc. These converters are developed in such vastly varying configurations to fulfill the very close and exact requirement in variety of applications. Some of these improved Power quality converters are improved to provide better performance from primitive configurations.

B. Current Control Techniques for PFC converters

      The current control techniques have gained importance in ac to dc converters used for high performance applications. Where the fast response and high accuracy are important. Various current control methods have been proposed and classified as hysteresis control, predictive control and linear control.

AUTOMATIC SUBSTATION CONTROL

   The electrical energy is transferred from large g enerating stations to distant load centres via various sub-stations. In every sub-station certain supervision, control and protection functions are necessary. Every substation has a control room. The relay and protection panels and control panels are installed in the control room. The various circuit breakers, tap changers and other devices are controlled by corresponding control-relay panels. In a small independent sub-station, the

supervision and operation for normal service can be carried out by the oper ator with the aid of analogue and digital control systems in the plant. The breakers can be operated by remote control from the control room. During faults and abnormal conditions, the breakers are operated by Protective relays automatically. Thus, the primary control in sub-station is of two categories.

1. Normal routine operation by operators command.

2. Automatic operation by action of protective relays and control systems.

SUB STATION CONTROL FUNCTION ARRANGED THROUGH SCADA SYSTEM:

1. Alarm Functions

    To sound alarm/annunciation regarding dangerous, uncommon events such as abnormal values of process parameters, fire, illegal entry in premises, over temperatures, low voltage of auxiliary supply, unusual happening etc. Alarms are obtained from data logger and are for alerting this operator in the control room.

2. Control and Indication

Control of two position devices such as circuit -breakers, isolators, earthing-switches,starters. Indication of ON/OFF state of the devices on control board/mimic diagrams.

Control of position of devices having positions (closed, middle open) e.g. values, input settings, indication of position on control panels.

Control positions of multi-position device e.g. tap changer, indication of position on control panels.

Indication without control.

Control without indication : e.g. raise or lower control of generator load by automatic load frequency control.

Set-point control to provide set point to a controller located at remote sub -station.

3. Data collection, recording, display.

4. Sequential operation of devices with predetermined time and conditions for operation of various devices e.g.

Auto-reclosing of circuit-breakers operation O-CO-Time-CO Operation of circuit-breaker, isolator and earthing switch in a particular sequence during opening of circuit and another sequence during closing of circuit.

5. By means of SCADA system, the operator in control centre can cause operations in a remote sub-station. The possible remote operations include :

Opening and closing of switching devices I

Tap-changing of transformers (voltage control)

 Switching of capacitor banks (voltage control)

 Load shedding (load frequency control)

6. Some of the remote operations are made automatic by one -line computer based system without human intervention e.g. Net work islanding, Backup protection. The automatic control function are segregated into :

 Interconnection functions

 Transmission line automatic function

 Distribution system automatic functions

WHAT IS SCADA AND ITS NEED:

SUPERVISORY CONTROL AND DATA ACQUISITION –we more frequently call it as SCADA. As the name implies SCADA system supervises, acquires and control data received from a distant data source from the control center. SCADA system is located in the control center and is operated in the scanning mode, communicating between the CONTROL CENTER and the REMOTE STATION by means of two-way communication channels. Such a supervisory control and data acquisition system is intended to facilitate the work of operator by acquiring and compiling information as well as locating, identifying and reporting faults. On the basis of information received, the operator makes necessary decisions via the control system he can the perform different control operations in power stations or influence the processing of 

information acquired. The main task of a modern day power system is to ensure quality and reliable power at an economic rate. Hence the system is to be updated at a very fast rate (real time mode/management), which helps to control the complex system effectively without any loss of time.

FUNCTIONS OF SCADA:

 DATA ACQUSITION- Furnishes status information & measurands data to operator

 CONTROL - Allows the operator to control the devices e.g. ckt breakers ,Xmer, tap changer etc from a remote centralised location .

DATA PROCESSING - Includes data quality & integrity check , limit check , analog value processing etc.

TAGGING - Operator identifies any specific device & subjects to specific operating restrictions to prevent from unauthorized operation.

ALARMS - Alerts the operator of unplanned events & undesirable operating conditions in the order their severity & criticality.

LOGGING- Logs all operator entries, alarms &selected entries.

TRENDING- Plots measurements on selected scale to give information on the trends e.g. one minute, one hour etc.

HISTORICAL REPORTING - To save & analyze the historical data for reporting, typically for a period of 2 or more years & to archive.

FUNCTIONAL UNITS OF SCADA:

 1.Data collection equipment.

2.Data transmission / telemetric equipment.

3. Remote terminal unit.

4. Data loggers.

5. Data presentation equipments.

HIGH FREQUENCY DC-DC CONVERTERS:

    In the past few years, the unprecedented demand for handheld electronic appliances and laptop computers with an ever-more impressive list of features and capabilities has meant more demand for processors. This demand directly translates to greater needs for higher current and power at voltages that will soon approach the fractional voltage range from the dc-dc converters in these appliances.

      These demands mean that converters must now be more efficient to allow for longer battery life, while fitting into ever-shrinking volumes and pc-board footprints. And, as if this were not a tough enough challenge for power-supply designers, better transient response and tighter load regulation are also required.

    To the experts it is clear that high switching-frequency operation — in the 5-MHz to 10-MHz range — is becoming mandatory. This single parameter holds the key to achieving designs that can meet all the demands of the next generation of portable appliances. 

     Higher switching frequencies will allow engineers to design supplies with considerably wider control-loop bandwidth, which is typically between a fifth and a tenth of the switching frequency. This is important because the wider the loop bandwidth, the fewer output filter capacitors needed, leading to cheaper design and smaller pc-board footprints. At present, a large number of output capacitors is needed in low switching-frequency applications to properly handle the large and fast transient load currents, while staying within transient voltage regulation limits. 

    As designs move to high switching frequencies, the filter inductor may also shrink, as less filter inductance is needed. This change further reduces the total volume occupied by the output filter and adds the benefit of lower cost. 

   The transition to 5-MHz to 10-MHz switching frequencies has been slow in coming due to the demands it places on almost all the components used in the design. Also, there is an immediate need for engineers to learn new processes for designing high current and high frequency converters. 

       For starters, if we really want to reap the full benefits of the high frequency approach, ceramic capacitors used in the output filter must be chosen to handle larger ripple currents for a given value and package at a lower effective series resistance for reduced output-ripple voltage. A variety of small-outline, low-profile, surface-mounted inductors are currently available for designs in the megahertz range and in the right inductance range of 30 nH to 100 nH. But some further reduction in size is still needed for currents in the neighborhood of 5 A to 10 A and even beyond to address the developing needs for the not-so-distant future. 

    This brings us to the switching power MOSFETs needed in these applications with their two ingredients, namely package and silicon technology. High frequency-power packages have matured in the last few years, and several packages are already available and can be used once this trend comes to fruition, becoming common practice. 

     Power-switching devices like MOSFETs that are used in these applications must offer low enough switching and conduction losses to achieve total power efficiencies of 85% to 95% at full current. At the same time, the control scheme must be designed to offer similar efficiencies across almost the entire range of load current to maximize the battery life. The demands on the power train create opportunities for the engineering community to develop the present topologies and/or invent new topologies and smarter gate drivers to deliver the performance levels needed. 

        In my opinion, the best approach would be “complete power modules” that are comprised of the controller, gate driver and switching devices where all the interfaces have been optimized to deliver the highest possible performance for a given application. Few such modules are available today from a small number of suppliers. Nevertheless, these modules open the door for further development to improve dc-dc converter performance in the portable and handheld market.

SOLVING MOTOR FAILURES DUE TO HIGH PEAK VOLTAGE AND FAST RIST TIME:

    The evolution of power semiconductors has been so dramatic that today an insulated gate bi-polar transistor (IGBT) can be turned on in just 0. I micro-second. This results in the voltage rising from zero to peak in only one-tenth of a microsecond. Unfortunately, there are many motors in existence that do not have sufficient insulation to operate under these conditions.

HIGH PEAK VOLTAGES

        High peak voltages can be experienced at the motor terminals especially when the distance between the inverter (drive) and the motor exceeds about 15 meters. This is typically caused by the voltage doubling phenomenon of a transmission line having unequal line and load impedance's. Motor terminal voltage can reach twice the DC bus voltage in long lead applications. When the characteristic load impedance is greater than the line impedance, then voltage (and current) is reflected from the load back toward the source (inverter). The absolute peak voltage is equal to the sum of the incident peak voltage traveling toward the motor plus the reflected peak voltage. If the load characteristic impedance is greater than the characteristic line impedance, then the highest peak voltage will be experienced at the load (motor) terminal. If the DC bus voltage is 850 volts, then motor terminal voltage could reach 1700 volts peak.

FAST VOLTAGE RISE TIMES:

Fast voltage rise times of 1600 volts per microsecond can be typical as the motor lead length exceeds just a few hundred feet. Voltage rise time is referred to as dv/dt(change in voltage versus change in time). When the rise time is very fast the motor insulation system becomes stressed. Excessively high dv/dt can cause premature breakdown of standard motor insulation. Inverter duty motors typically have more phase-to-phase and slot insulation than standard duty motors (NEMA design B).

         When motors fail due to insulation stress caused by high peak voltage and fast voltage rise times (high dv/dt) they have common symptoms. Most failures of these types occur in the first turn as either a phase-to-phase short or phase to stator short. The highest voltage is seen by the first turn of the winding and due to motor inductance and winding capacitance of the motor, the peak voltage and dv/dt decay rapidly as the voltage travels through the winding. Normally, the turn to turn voltage in a motor is quite low because there are many turns in the winding. However, when the dv/dt is very high the voltage gradient between turns and between phase windings can be excessively high, resulting in premature breakdown of the motor insulation system and ultimately motor failure. This problem is most prevalent on higher system voltages (480 & 600 volts) because the peak terminal voltage experienced often exceeds the insulation breakdown voltage rating of the motor.

STANDARD MOTOR CAPABILITIES

      Standard Motor Capabilities established by the National Electrical Manufacturers Association (NEMA)and expressed in the MG- I standard (part 30), indicate that standard NEMA type B motors can withstand 1000 volts peak at a minimum rise time of 2 u-sec (microseconds). Therefore to protect standard NEMA Design B motors, one should limit peak voltage to 1KV and reduce the voltage rise to less than 500 volts per micro-second.

SOLUTIONS

     There are several solutions available to solve this problem, each offering a different degree of protection at a different price.

1. Inverter Duty motors should be considered for all new IGBT drive installations. They offer increased winding slot insulation, increased first turn insulation, and increased phase- to-phase turn insulation. They are more expensive than standard design B motors but are the best motor for the job when it will be controlled by an IGBT variable frequency inverter. The NEMA Standard MG- I (part 3 1) indicates that inverter duty motors shall be designed to withstand 1600 volts peak and rise times of >0.1µsec. Nevertheless, it is wise to confirm the actual motor capability with the manufacturer.

2. Minimize Cable Length between the inverter and motor. Quite often this is somewhat uncontrollable, especially when the application is downhole pumping where the motor is required to be a great distance from the inverter. The longer the cable, the greater the capacitance of the cable, the lower the impedance of the cable and thus a greater mis-match will result between the characteristic line and load impedance's, resulting in higher peak voltage at the motor (load) terminals. Minimize this length whenever possible to avoid problems.

   3. Tuned Inductor & Capacitor (LC) Filters are an effective means of taming the output voltage waveform and protecting the motor. An "LC" circuit can result in the best voltage waveform but at a relatively high cost and with some future considerations. Of course these filters are "low pass shunt type filters" tuned for some specific frequency, often in the range of 1 kHz to 2Khz. Because these filters have essentially zero impedance at there resonant frequency, it is very important that the inverter switching frequency not be set too low. The threat exists that someone may vary the carrier frequency (at a later date) without consideration for the existence of a low pass filter resulting in damage to the inverter or filter. One should be very careful when applying this type of filter on the output of an inverter with variable carrier frequency. LC filters for this purpose cost approximately 3-4 times the cost of a load reactor.

   4. RC Snubber Networks can reduce the slope of the voltage waveform leading edge and reduce the peak voltage of the waveform but they have a minimal effect on the actual waveshape. They perform marginally when compared to the other solutions discussed herein. At an intermediate cost, they provide a marginal benefit. The cost of these network can be 2-3 times the cost of a load reactor.

   5. Load Reactors are the most cost effective means of solving high dv/dt and peak voltage problems associated with IGBT inverters. Typical experience is that peak voltage is limited to I 000 volts or less (actual value varies based upon system voltage). Voltage rise time (dv/dt) is typically extended to several micro-seconds resulting in only about 75 - 200 volts per micro- second rise times. Usually the load reactor is all that is needed to adequately protect the motor from dv/dt and to allow full warranty of the motor in IGBT inverter applications. (Some motor manufacturers do not offer a warranty in IGBT applications if a load reactor is not installed).

    Whether you install the load reactor at the inverter or at the motor, it will provide you with protection for your motor. It offers the best dv/dt reduction when it is placed at the inverter and this is usually the easiest place to add the reactor. Placement at the inverter also provides voltage stress protection for the motor cables. Of course there are some applications that may require the addition of the load reactor at the motor terminals. This will also provide very good protection of the motor because the IGBT protected reactor acts like the first turns of the motor. The motor is protected well in this case, however the motor cables are not protected from voltage stress.

GUARD-AC LINE/LOAD REACTORS

"Guard-Ac" Line/Load Reactors manufactured by MTE Corporation, are specially constructed with IGBT protection.

They have a 4000 volt rms(5600Vpeak) insulation dielectric strength and are approved by both CSA and UL (UL506 & UL508). Only reactors approved to UL506 have the high dielectric strength (4000 volts) required for IGBT applications.

MTE Corporation Line/Load reactors also feature "Triple Insulation" on the first two and last two turns of each coil providing over 10,000 volts strength. Our standard Line/Load Reactors are suitable for use on IGBT inverter outputs with switching frequencies up to 20Khz. 

HELPING MOTORS TO KEEP THEIR COOL:

An electric motor's insulation system separates electrical components from each other, preventing short circuits and thus, winding burnout and failure. Insulation's major enemy is heat, so it's important to be sure to keep the motor within temperature limits. There is a rule of thumb that says a 10 degree Celsius (1299 degrees Fahrenheit) rise reduces the insulation's useful life by half, while a 10 degree Celsius (50 degrees Fahrenheit) decrease doubles the insulation's life. This implies that if you can keep a motor cool enough, the winding will last forever, which ignores factors like moisture, vibration, chemicals and abrasives in the air that also attack insulation systems.

     The real issue is at what temperature the motor windings are designed to operate for a long and predictable insulation life?20,000 hours or more. NEMA, the National Electrical Manufacturers Association, sets temperature standards based on thermal classes, the most common being A, B, F and H. The accompanying table provides a summary.

      Class B or Class F insulation systems are usually used in today's industrial-duty NEMA "T frame" motors. Many manufacturers also design their motors to operate cooler than their thermal class might allow. For example, a motor might have Class F insulation but a Class B temperature rise. This gives an extra thermal margin. Class H insulation systems are seldom found in general-purpose motors, but rather in special designs for very heavy-duty use, high ambient temperature or high altitudes.

     Class A insulation, while not used on today's industrial-duty motors, was standard on industrial "U frame" motors built in the 1960s and earlier. Because Class A insulation has such a low temperature rating, older motors were required to have far lower maximum temperatures. This accounts for the perception among many long-time motor users that modern motors "run hot." In fact, they do compared with older motors, but modern insulation systems are so much better that the reliability and durability of new motors are equal to or better than older-design motors. Plus, better insulation systems have allowed motor manufacturers to put more horsepower in a smaller package.

Determining Correct Operation:

     Though many people believe they can judge a motor's operating characteristics by feeling its surface, that really isn't a very effective method. Design ratings for temperature apply to the hottest spot within the motor's windings, not how much of that heat is transferred to the motor's surface. Unless you have intimate knowledge of a specific motor model's design?including benchmark lab readings of heat runs that show "normal" surface temperatures for that specific model in exact locations on the frame?a motor's "skin temperature" provides little if any evidence of what's going on inside. This is true even if temperature measurement methods far more sophisticated than the human touch are used. In addition, for safety reasons, it is unwise to touch operating motors anyway.

     Specifying motors with inherent overload protectors, thermostats or resistive temperature devices, or installing similar protection in motor controls, can help ensure that a motor is taken off-line before winding damage occurs. Motor protection of one sort or another is advisable in almost any application. A common and reliable field test for motor heating involves checking the motor?s amp draw with a clamp-style ammeter. Use this to confirm that actual amps are less than or equal to the nameplate rating. A precise test for winding temperature is the resistance method. This involves careful measurements with sensitive equipment, calculations and several hours of time. Procedures to conduct such tests can be found in technical manuals. Or contact your motor manufacturer.

Common Sense Precautions:

     Sometimes a motor overheats because of a manufacturing or design defect. But far more often, overheating can be traced to misapplication. Overloading is the leading cause. This could take the form of using an undersized motor, a situation that may become more common as concern for energy efficiency puts the emphasis on eliminating oversized motors. Use an 80% loading as your guide. Most electric motors reach their peak efficiency at that load, and a comfortable overload margin remains.

     Other common causes of overloading include a load seizing up or misalignment of power transmission linkages. Plus, unanticipated changes in environment, aging of equipment, misuse and other factors can subject the motor to stresses for which it was not intended.

     Environmental conditions that can result in motor overheating include high ambients (especially look at the near vicinity of the motor for any heat-generating device) and high altitudes, (above 3,300 feet (1005.84m), where the "thin" air has less cooling potential). You might have to derate a motor under these conditions, probably choosing the next size up. Another environmental concern is dirt and fibers, which can clog ventilation openings, coat heat dissipating surfaces and cause a variety of mechanical problems.

     Power supply problems are another overheating cause. Low voltage will result in the motor drawing higher current to deliver the same horsepower, and the higher current means higher winding temperatures. A 10% drop in voltage could cause nearly that much greater temperature rise. Excessive or sustained high voltage will saturate a motor's core and lead to overheating as well. In three-phase motors, phase imbalances can result in high currents and excessive heat, the extreme being the complete loss of voltage in one phase (called single phasing), which, if correct protection is not in place, will result in motor burnout.

     Often overlooked as a cause of overheating is the number of start/stop cycles. It's not uncommon for a motor at starting to draw five times or more the current it does while running. This accelerates heating dramatically. Though various provisions are made relative to loading and off-time, NEMA essentially limits a three-phase continuous-duty motor to two starts in succession before allowing sufficient time for the motor to stabilize to its maximum continuous operating temperature rating. This is highly application-dependent, so it's best to check with your motor manufacturer if you're facing a high-cycle application.

     Finally, pay special attention when applying adjustable-speed inverter drives, especially if you are introducing an inverter in a system of older motors. Some additional heating to the motor windings will inevitably occur because of the inverter's "synthesized" AC wave form. A greater cooling concern involves operating for an extended time at low motor RPM, which reduces the flow of cooling air. Modern inverter-duty motors have higher insulation ratings to help alleviate this concern, and the robust insulation systems used in most of today's general-purpose industrial motors are adequate for many applications as well. In extreme cases, however, secondary cooling such as a special lower may be required.

EXTENDED MOTOR LIFE WITH BEARING CARE:

     Bearing failures are the root cause for the great majority of electric motor downtime, repair and replacement costs. Bearing and motor manufacturers are aware of the situation. Motor repair shops can attribute much of their business to bearing failures. And motor users see bearing failure as the fundamental cause of virtually every electric motor repair expense. Studies conducted by the Electrical Apparatus Service Association also demonstrate that bearing failures are by far the most common cause of motor failures.

       Knowing that shaft bearings are the Achilles’ heel of industrial electric motors is not a new idea in maintenance departments, but what is new is recognizing that something can be done to prevent most motor bearing failures.

Factors affecting bearing failure:

        Electric motors actually present a relatively easy duty for shaft bearings. The motor rotor is lightweight, yet because of its large shaft diameter, the bearings are large. For example, the bearings supporting the 140 lb. Rotor for a typical 40 hp. 1800 rpm industrial motor are so large that they have an L-10 minimum design fatigue life of 3000 years, or 10 percent of the bearings are statistically expected to fail from fatigue after 3000 years of operation. Plant operating experience, however, strongly contradicts such optimistic estimates of motor bearing life. In actual industrial environments, bearing failure is rarely caused by fatigue; it is caused by less-than-ideal lubrication. Because of contaminated lubrication, bearings fail well before they serve their theoretical fatigue life. There are many reasons for less than-ideal bearing lubrication. Lubricants can leak out; chemical attacks or thermal conditions can decompose or break down lubricants; lubricants can become contaminated with non-lubricants such as water, dust, or rust from the bearings themselves. These lubrication problems can be eliminated. Motor bearings can last virtually forever by simply providing an ideal contamination-free, well-lubricated bearing environment. Conventional wisdom teaches that such an ideal motor bearing environment can be provided by using a dry-running lip seal or using sealed (lubricated-for-life) bearings.

      Indeed, for many light-duty applications, such bearing protection techniques are often sufficient to allow bearings to last as long as the equipment itself. However, these bearing protection methods have not significantly reduced the rate of bearing failure in severe-duty industrial motors.

    Bearings in industrial applications continue to fail because of inadequate lubrication caused by lubricant loss, contamination, and decomposition and break-down. Lip seals invariably wear out well before the bearing fails, and sealed bearings inherently foreshorten the life of a bearing to the service life of the contained grease (usually only about 3,000 to 5,000 hours for most industrial services).

       Maintenance professionals may find the following suggestions on how to forestall motor hearing failure obvious, but some new techniques and technologies are available.

Lubricate Bearing at Correct Intervals: 

     Despite years of warnings from bearing manufacturers, over lubrication continues to plague many motor bearings. Too much grease can cause overheating of the bearings. The lubrication instructions supplied by the motor manufacturer will specify the quantity and frequency of lubrication. Generally, two-pole motors should be greased twice a year, four-pole and slower motors only once a year.

use the best available grease:

     The most commonly used bearing grease is polyurea-based, a low-cost, low-performance, highly compatible lubricant. However, it does not handle water well, a serious drawback for many industrial applications. It reacts readily with water and loses its ability to lubricate bearings.

      Industrial motor bearings should be lubricated with a synthetic-based aluminum complex grease. A high-quality grease pays for its additional cost in reduced motor downtime and repair costs.

Keep Out Moisture:

      Unless the motor is being hosed down or it operates in a humid environment, reasonably shielded motor bearings may not become seriously contaminated with moisture while the motor is running. However, when the rotor is shut down, moisture and condensation can collect on the surface of the bearing components. Eventually, this water breaks through the oil and grease barrier, contacts the metal parts of the bearing, and produces tiny particles of iron oxide. These rust particles make an excellent grinding compound when mixed with the grease. resulting in premature failure of the bearing because of surface degradation.

      Preventing water contamination is a major challenge to bearing housing design. Close shaft-to-endbell clearances cannot stop the movement of humid air. Contact seals will quit contacting, resulting in large gaps that allow movement of air and water vapor across the bearing. 

        Vapor-blocking bearing isolators, such as the one illustrated, are among the more successful devices presently available to prevent water vapor from entering a stationary bearing. When the motor shaft is rotating, the isolator opens, eliminating the possibility of friction and wear. However, when the shaft is stationary, the isolator closes, preventing movement of air or water across its face. With no wear from rotating friction, the seal may last indefinitely, and surely as long as the fatigue-failure life of the bearing.

Keep Out Dirt:

      Lip seals, contact seals, and frequent grease replacement help minimize the amount of dirt and other air-borne abrasives that can contaminate bearing lubricant. These solutions, however, have some drawbacks. Lip seals have a short service life, and frequent grease displacement is expensive and messy.

    One successful approach to keeping air-borne dirt and liquids out of an operating bearing is to install a labyrinth-type non-contact seal over the bearing housing. These bearing isolators, readily available from suppliers, combine a tortuous labyrinth path with impingement and centrifugal forces to trap and remove air-borne dirt and liquid; virtually no contamination can reach the bearing. Because the bearing isolator is a non-contact device, it will generally be the longest-lasting component of the motor.

      Although not intended as such, a bearing isolator could serve as an emergency sleeve bearing if the primary bearing fails, possibly preventing damage to the motor’s stator and rotor. In emergency situations, the bearing isolator can allow continued operation for a short time and still prevent the need to rewind the motor when the bearing is replaced. Bearing isolators constructed of bronze or other non-sparking materials also can prevent hazardous sparks that could otherwise occur when the bearing’s rolling elements fail.