Protective devices and power systems in practice?

Protective devices

Introduction

Power systems contain protective devices to prevent injury or damage during failures. The quintessential protective device is the fuse. When the current through a fuse exceeds a certain threshold, the fuse element melts, producing an arc across the resulting gap that is then extinguished, interrupting the circuit. Given that fuses can be built as the weak point of a system, fuses are ideal for protecting circuitry from damage. Fuses however have two problems: First, after they have functioned, fuses must be replaced as they cannot be reset. This can prove inconvenient if the fuse is at a remote site or a spare fuse is not on hand. And second, fuses are typically inadequate as the sole safety device in most power systems as they allow current flows well in excess of that that would prove lethal to a human or animal.

Fuse plus circuit breaker

The first problem is resolved by the use of circuit breakers—devices that can be reset after they have broken current flow. In modern systems that use less than about 10 kW, miniature circuit breakers are typically used. These devices combine the mechanism that initiates the trip (by sensing excess current) as well as the mechanism that breaks the current flow in a single unit. Some miniature circuit breakers operate solely on the basis of electromagnetism. In these miniature circuit breakers, the current is run through a solenoid, and, in the event of excess current flow, the magnetic pull of the solenoid is sufficient to force open the circuit breaker's contacts (often indirectly through a tripping mechanism). A better design however arises by inserting a bimetallic strip before the solenoid—this means that instead of always producing a magnetic force, the solenoid only produces a magnetic force when the current is strong enough to deform the bimetallic strip and complete the solenoid's circuit.

Relays

In higher powered applications, the protective relays that detect a fault and initiate a trip are separate from the circuit breaker. Early relays worked based upon electromagnetic principles similar to those mentioned in the previous paragraph, modern relays are application-specific computers that determine whether to trip based upon readings from the power system. Different relays will initiate trips depending upon different protection schemes. For example, an overcurrent relay might initiate a trip if the current on any phase exceeds a certain threshold whereas a set of differential relays might initiate a trip if the sum of currents between them indicates there may be current leaking to earth. The circuit breakers in higher powered applications are different too. Air is typically no longer sufficient to quench the arc that forms when the contacts are forced open so a variety of techniques are used. One of the most popular techniques is to keep the chamber enclosing the contacts flooded with sulfur hexafluoride (SF6)—a non-toxic gas that has sound arc-quenching properties. Other techniques are discussed in the reference.

Residual current devices

The second problem, the inadequacy of fuses to act as the sole safety device in most power systems, is probably best resolved by the use of residual current devices (RCDs). In any properly functioning electrical appliance the current flowing into the appliance on the active line should equal the current flowing out of the appliance on the neutral line. A residual current device works by monitoring the active and neutral lines and tripping the active line if it notices a difference. Residual current devices require a separate neutral line for each phase and to be able to trip within a time frame before harm occurs. This is typically not a problem in most residential applications where standard wiring provides an active and neutral line for each appliance (that's why your power plugs always have at least two tongs) and the voltages are relatively low however these issues do limit the effectiveness of RCDs in other applications such as industry. Even with the installation of an RCD, exposure to electricity can still prove lethal.

SCADA systemsST

In large electric power systems, Supervisory Control And Data Acquisition (SCADA) is used for tasks such as switching on generators, controlling generator output and switching in or out system elements for maintenance. The first supervisory control systems implemented consisted of a panel of lamps and switches at a central console near the controlled plant. The lamps provided feedback on the state of plant (the data acquisition function) and the switches allowed adjustments to the plant to be made (the supervisory control function). Today, SCADA systems are much more sophisticated and, due to advances in communication systems, the consoles controlling the plant no longer need to be near the plant itself. Instead it is now common for plants to be controlled with equipment similar (if not identical) to a desktop computer. The ability to control such plants through computers has increased the need for security—there have already been reports of cyber-attacks on such systems causing significant disruptions to power systems.

Power systems in practice

Despite their common components, power systems vary widely both with respect to their design and how they operate. This section introduces some common power system types and briefly explains their operation.

Residential power system

Residential dwellings almost always take supply from the low voltage distribution lines or cables that run past the dwelling. These operate at voltages of between 110 and 260 volts (phase-to-earth) depending upon national standards. A few decades ago small dwellings would be fed a single phase using a dedicated two-core service cable (one core for the active phase and one core for the neutral return). The active line would then be run through a main isolating switch in the fuse box and then split into one or more circuits to feed lighting and appliances inside the house. By convention, the lighting and appliance circuits are kept separate so the failure of an appliance does not leave the dwelling's occupants in the dark. All circuits would be fused with an appropriate fuse based upon the wire size used for that circuit. Circuits would have both an active and neutral wire with both the lighting and power sockets being connected in parallel. Sockets would also be provided with a protective earth. This would be made available to appliances to connect to any metallic casing. If this casing were to become live, the theory is the connection to earth would cause an RCD or fuse to trip—thus preventing the future electrocution of an occupant handling the appliance. Earthing systems vary between regions, but in countries such as the United Kingdom and Australia both the protective earth and neutral line would be earthed together near the fuse box before the main isolating switch and the neutral earthed once again back at the distribution transformer.

There have been a number of minor changes over the year to practice of residential wiring. Some of the most significant ways modern residential power systems tend to vary from older ones include:

For convenience, miniature circuit breakers are now almost always used in the fuse box instead of fuses as these can easily be reset by occupants.

For safety reasons, RCDs are now installed on appliance circuits and, increasingly, even on lighting circuits.

Dwellings are typically connected to all three-phases of the distribution system with the phases being arbitrarily allocated to the house's single-phase circuits.

Whereas air conditioners of the past might have been fed from a dedicated circuit attached to a single phase, centralised air conditioners that require three-phase power are now becoming common.

Protective earths are now run with lighting circuits to allow for metallic lamp holders to be earthed.

Increasingly residential power systems are incorporating microgenerators, most notably, photovoltaic cells.

Commercial power systems

Commercial power systems such as shopping centers or high-rise buildings are larger in scale than residential systems. Electrical designs for larger commercial systems are usually studied for load flow, short-circuit fault levels, and voltage drop for steady-state loads and during starting of large motors. The objectives of the studies are to assure proper equipment and conductor sizing, and to coordinate protective devices so that minimal disruption is cause when a fault is cleared. Large commercial installations will have an orderly system of sub-panels, separate from the main distribution board to allow for better system protection and more efficient electrical installation.

Typically one of the largest appliances connected to a commercial power system is the HVAC unit, and ensuring this unit is adequately supplied is an important consideration in commercial power systems. Regulations for commercial establishments place other requirements on commercial systems that are not placed on residential systems. For example, in Australia, commercial systems must comply with AS 2293, the standard for emergency lighting, which requires emergency lighting be maintained for at least 90 minutes in the event of loss of mains supply. In the United States, the National Electrical Code requires commercial systems to be built with at least one 20A sign outlet in order to light outdoor signage. Building code regulations may place special requirements on the electrical system for emergency lighting, evacuation, emergency power, smoke control and fire protection.

What is Power engineering?

Introduction

Power engineering, also called power systems engineering, is a subfield of energy engineering and electrical engineering that deals with the generation, transmission, distribution and utilization of electric power and the electrical devices connected to such systems including generators, motors and transformers. Although much of the field is concerned with the problems of three-phase AC power – the standard for large-scale power transmission and distribution across the modern world – a significant fraction of the field is concerned with the conversised in aircraft or for electric railway networks. Power engineering draws the majority of its theoretical base from electrical engineering and while some power engineers could be considered energy engineers, energy engineers often do not have the theoretical electrical engineering background to understand power engineering.

Basics of electric power

An external AC to DC power adapter used for household appliances

Electric power is the mathematical product of two quantities: current and voltage. These two quantities can vary with respect to time (AC power) or can be kept at constant levels (DC power).

Most refrigerators, air conditioners, pumps and industrial machinery use AC power whereas computers and digital equipment use DC power (the digital devices you plug into the mains typically have an internal or external power adapter to convert from AC to DC power). AC power has the advantage of being easy to transform between voltages and is able to be generated and utilised by brushless machinery. DC power remains the only practical choice in digital systems and can be more economical to transmit over long distances at very high voltages (see HVDC).

The ability to easily transform the voltage of AC power is important for two reasons: Firstly, power can be transmitted over long distances with less loss at higher voltages. So in power networks where generation is distant from the load, it is desirable to step-up the voltage of power at the generation point and then step-down the voltage near the load. Secondly, it is often more economical to install turbines that produce higher voltages than would be used by most appliances, so the ability to easily transform voltages means this mismatch between voltages can be easily managed.

Solid state devices, which are products of the semiconductor revolution, make it possible to transform DC power to different voltages, build brushless DC machines and convert between AC and DC power. Nevertheless, devices utilising solid state technology are often more expensive than their traditional counterparts, so AC power remains in widespread use.

Power

Transmission lines transmit power across the grid.

Power Engineering deals with the generation, transmission, distribution and utilization of electricity as well as the design of a range of related devices. These include transformers, electric generators, electric motors and power electronics.

The power grid is an electrical network that connects a variety of electric generators to the users of electric power. Users purchase electricity from the grid so that they do not need to generate their own. Power engineers may work on the design and maintenance of the power grid as well as the power systems that connect to it. Such systems are called on-grid power systems and may supply the grid with additional power, draw power from the grid or do both. The grid is designed and managed using software that performs simulations of power flows.

Power engineers may also work on systems that do not connect to the grid. These systems are called off-grid power systems and may be used in preference to on-grid systems for a variety of reasons. For example, in remote locations it may be cheaper for a mine to generate its own power rather than pay for connection to the grid and in most mobile applications connection to the grid is simply not practical.

Today, most grids adopt three-phase electric power with alternating current. This choice can be partly attributed to the ease with which this type of power can be generated, transformed and used. Often (especially in the United States), the power is split before it reaches residential customers whose low-power appliances rely upon single-phase electric power. However, many larger industries and organizations still prefer to receive the three-phase power directly because it can be used to drive highly efficient electric motors such as three-phase induction motors.

Transformers play an important role in power transmission because they allow power to be converted to and from higher voltages. This is important because higher voltages suffer less power loss during transmission. This is because higher voltages allow for lower current to deliver the same amount of power, as power is the product of the two. Thus, as the voltage steps up, the current steps down. It is the current flowing through the components that result in both the losses and the subsequent heating. These losses, appearing in the form of heat, are equal to the current squared times the electrical resistance through which the current flows, so as the voltage goes up the losses are dramatically reduced.

For these reasons, electrical substations exist throughout power grids to convert power to higher voltages before transmission and to lower voltages suitable for appliances after transmission.

Components

Power engineering is a network of interconnected components which convert different forms of energy to electrical energy. Modern power engineering consists of four main subsystems: the generation subsystem, the transmission subsystem, the distribution subsystem and the utilization subsystem. In the generation subsystem, the power plant produces the electricity. The transmission subsystem transmits the electricity to the load centers. The distribution subsystem continues to transmit the power to the customers. The utilization system is concerned with the different uses of electrical energy like illumination, refrigeration, traction, electric drives, etc. Utilization is a very recent concept in Power engineering.

Generation

Generation of electrical power is a process whereby energy is transformed into an electrical form. There are several different transformation processes, among which are chemical, photo-voltaic, and electromechanical. Electromechanical energy conversion is used in converting energy from coal, petroleum, natural gas, uranium, or water flow into electrical energy. Of these, all except the wind energy conversion process take advantage of the synchronous AC generator coupled to a steam, gas or hydro turbine such that the turbine converts steam, gas, or water flow into rotational energy, and the synchronous generator then converts the rotational energy of the turbine into electrical energy. It is the turbine-generator conversion process that is by far most economical and consequently most common in the industry today.

The AC synchronous machine is the most common technology for generating electrical energy. It is called synchronous because the composite magnetic field produced by the three stator windings rotate at the same speed as the magnetic field produced by the field winding on the rotor. A simplified circuit model is used to analyze steady-state operating conditions for a synchronous machine. The phasor diagram is an effective tool for visualizing the relationships between internal voltage, armature current, and terminal voltage. The excitation control system is used on synchronous machines to regulate terminal voltage, and the turbine-governor system is used to regulate the speed of the machine. However, in highly interconnected systems, such as the "Western system", the "Texas system" and the "Eastern system", one machine will usually be assigned as the so-called "swing machine", and which generation may be increased or decreased to compensate for small changes in load, thereby maintaining the system frequency at precisely 60 Hz. Should the load dramatically change, as happens with a system separation, then a combination of "spinning reserve" and the "swing machine" may be used by the system's load dispatcher.

The operating costs of generating electrical energy is determined by the fuel cost and the efficiency of the power station. The efficiency depends on generation level and can be obtained from the heat rate curve. The incremental cost curve may also be derived from the heat rate curve. Economic dispatch is the process of allocating the required load demand between the available generation units such that the cost of operation is minimized. Emission dispatch is the process of allocating the required load demand between the available generation units such that air pollution occurring from operation is minimized. In large systems, particularly in the West, a combination of economic and emission dispatch may be used.

Transmission

The electricity is transported to load locations from a power station to a transmission subsystem. Therefore, we may think of the transmission system as providing the medium of transportation for electric energy. The transmission system may be subdivided into the bulk transmission system and the sub-transmission system. The functions of the bulk transmission are to interconnect generators, to interconnect various areas of the network, and to transfer electrical energy from the generators to the major load centers. This portion of the system is called "bulk" because it delivers energy only to so-called bulk loads such as the distribution system of a town, city, or large industrial plant. The function of the sub-transmission system is to interconnect the bulk power system with the distribution system.

Transmission circuits may be built either underground or overhead. Underground cables are used predominantly in urban areas where acquisition of overhead rights of way are costly or not possible. They are also used for transmission under rivers, lakes and bays. Overhead transmission is used otherwise because, for a given voltage level, overhead conductors are much less expensive than underground cables.

transmission lines

The transmission system is a highly integrated system. It is referred to as the substation equipment and transmission lines. The substation equipment contain the transformers, relays, and circuit breakers. Transformers are important static devices which transfer electrical energy from one circuit to another in the transmission subsystem. Transformers are used to step up the voltage on the transmission line to reduce the power loss which is dissipated on the way. A relay is functionally a level-detector; they perform a switching action when the input voltage (or current) meets or exceeds a specific and adjustable value. A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. A change in the status of any one component can significantly affect the operation of the entire system. Without adequate contact protection, the occurrence of undesired electric arcing causes significant degradation of the contacts, which suffer serious damage.There are three possible causes for power flow limitations to a transmission line. These causes are thermal overload, voltage instability, and rotor angle instability. Thermal overload is caused by excessive current flow in a circuit causing overheating. Voltage instability is said to occur when the power required to maintain voltages at or above acceptable levels exceeds the available power. Rotor angle instability is a dynamic problem that may occur following faults, such as short circuit, in the transmission system. It may also occur tens of seconds after a fault due to poorly damped or undamped oscillatory response of the rotor motion. As long as the equal area criteria is maintained, the interconnected system will remain stable. Should the equal area criteria be violated, it becomes necessary to separate the unstable component from the remainder of the system.

Distribution

The distribution system transports the power from the transmission system/substation to the customer. Distribution feeders can be radial or networked in an open loop configuration with a single or multiple alternate sources. Rural systems tend to be of the former and urban systems the latter. The equipment associated with the distribution system usually begins downstream of the distribution feeder circuit breaker. The transformer and circuit breaker are usually under the jurisdiction of a "substations department". The distribution feeders consist of combinations of overhead and underground conductor, 3 phase and single phase switches with load break and non-loadbreak ability, relayed protective devices, fuses, transformers (to utilization voltage), surge arresters, voltage regulators and capacitors.

More recently, Smart Grid initiatives are being deployed so that: One, distribution feeder faults are automatically isolated and power restored to unfaulted circuits by automatic hardware/software/communications packages. And two, capacitors are automatically switched on or off to dynamically control VAR flow and for CVR (Conservation Voltage Reduction).

Utilization

Utilization is the “end result” of the generation, transmission, and distribution of electric power. The energy carried by the transmission and distribution system is turned into useful work, light, heat, or a combination of these items at the utilization point. Understanding and characterizing the utilization of electric power is critical for proper planning and operation of power systems. Improper characterization of utilization can result of over or under building of power system facilities and stressing of system equipment beyond design capabilities. The term load refers to a device or collection of devices that draw energy from the power system. Individual loads (devices) range from small light bulbs to large induction motors to arc furnaces. The term load is often somewhat arbitrarily applied, at times being used to describe a specific device, and other times referring to an entire facility and even being used to describe the lumped power requirements of power system components and connected utilization devices downstream of a specific point in large scale system studies.

A major application of electric energy is in its conversion to mechanical energy. Electromagnetic, or “EM” devices designed for this purpose are commonly called “motors.” Actually the machine is the central component of an integrated system consisting of the source, controller, motor, and load. For specialized applications, the system may be, and frequently is, designed as an integrated whole. Many household appliances (e.g., a vacuum cleaner) have in one unit, the controller, the motor, and the load.Courtesy of wikipedia.com

Bulk power transmission?

Introduction

A transmission substation decreases the voltage of incoming electricity, allowing it to connect from long distance high voltage transmission, to local lower voltage distribution. It also reroutes power to other transmission lines that serve local markets. This is the PacifiCorp Hale Substation, Orem, Utah, USA
Engineers design transmission networks to transport the energy as efficiently as feasible, while at the same time taking into account economic factors, network safety and redundancy. These networks use components such as power lines, cables, circuit breakers, switches and transformers. The transmission network is usually administered on a regional basis by an entity such as a regional transmission organization or transmission system operator.

Efficiency

Transmission efficiency is greatly improved by devices that increase the voltage (and thereby proportionately reduce the current), in the line conductors, thus allowing power to be transmitted with acceptable losses. The reduced current flowing through the line reduces the heating losses in the conductors. According to Joule's Law, energy losses are directly proportional to the square of the current. Thus, reducing the current by a factor of two will lower the energy lost to conductor resistance by a factor of four for any given size of conductor.

Size of conductor

The optimum size of a conductor for a given voltage and current can be estimated by Kelvin's law for conductor size, which states that the size is at its optimum when the annual cost of energy wasted in the resistance is equal to the annual capital charges of providing the conductor. At times of lower interest rates, Kelvin's law indicates that thicker wires are optimal; while, when metals are expensive, thinner conductors are indicated: however, power lines are designed for long-term use, so Kelvin's law has to be used in conjunction with long-term estimates of the price of copper and aluminum as well as interest rates for capital.

Voltage increment

The increase in voltage is achieved in AC circuits by using a step-up transformer. HVDC systems require relatively costly conversion equipment which may be economically justified for particular projects such as submarine cables and longer distance high capacity point to point transmission. HVDC is necessary for the import and export of energy between grid systems that are not synchronized with each other.

A transmission grid is a network of power stations, transmission lines, and substations. Energy is usually transmitted within a grid with three-phase AC. Single-phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors. In the 19th century, two-phase transmission was used but required either four wires or three wires with unequal currents. Higher order phase systems require more than three wires, but deliver little or no benefit.

The synchronous grids of the European Union

The price of electric power station capacity is high, and electric demand is variable, so it is often cheaper to import some portion of the needed power than to generate it locally. Because loads are often regionally correlated (hot weather in the Southwest portion of the US might cause many people to use air conditioners), electric power often comes from distant sources. Because of the economic benefits of load sharing between regions, wide area transmission grids now span countries and even continents. The web of interconnections between power producers and consumers should enable power to flow, even if some links are inoperative.

The unvarying (or slowly varying over many hours) portion of the electric demand is known as the base load and is generally served by large facilities (which are more efficient due to economies of scale) with fixed costs for fuel and operation. Such facilities are nuclear, coal-fired or hydroelectric, while other energy sources such as concentrated solar thermal and geothermal power have the potential to provide base load power. Renewable energy sources, such as solar photovoltaics, wind, wave, and tidal, are, due to their intermittency, not considered as supplying "base load" but will still add power to the grid. The remaining or 'peak' power demand, is supplied by peaking power plants, which are typically smaller, faster-responding, and higher cost sources, such as combined cycle or combustion turbine plants fueled by natural gas.

Long distance transmission

Long-distance transmission of electricity (thousands of kilometers) is cheap and efficient, with costs of US$0.005–0.02/kWh (compared to annual averaged large producer costs of US$0.01–0.025/kWh, retail rates upwards of US$0.10/kWh, and multiples of retail for instantaneous suppliers at unpredicted highest demand moments). Thus distant suppliers can be cheaper than local sources (e.g., New York often buys over 1000 MW of electricity from Canada). Multiple local sources (even if more expensive and infrequently used) can make the transmission grid more fault tolerant to weather and other disasters that can disconnect distant suppliers.


A high-power electrical transmission tower, 230 kV, double-circuit, also double-bundled
Long-distance transmission allows remote renewable energy resources to be used to displace fossil fuel consumption. Hydro and wind sources cannot be moved closer to populous cities, and solar costs are lowest in remote areas where local power needs are minimal. Connection costs alone can determine whether any particular renewable alternative is economically sensible. Costs can be prohibitive for transmission lines, but various proposals for massive infrastructure investment in high capacity, very long distance super grid transmission networks could be recovered with modest usage fees.

Grid input

At the power stations, the power is produced at a relatively low voltage between about 2.3 kV and 30 kV, depending on the size of the unit. The generator terminal voltage is then stepped up by the power station transformer to a higher voltage (115 kV to 765 kV AC, varying by the transmission system and by country) for transmission over long distances.

Losses

Transmitting electricity at high voltage reduces the fraction of energy lost to resistance, which varies depending on the specific conductors, the current flowing, and the length of the transmission line. For example, a 100-mile (160 km) 765 kV line carrying 1000 MW of power can have losses of 1.1% to 0.5%. A 345 kV line carrying the same load across the same distance has losses of 4.2%. For a given amount of power, a higher voltage reduces the current and thus the resistive losses in the conductor. For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the I2R losses by a factor of 100, provided the same sized conductors are used in both cases. Even if the conductor size (cross-sectional area) is reduced 10-fold to match the lower current, the I2R losses are still reduced 10-fold. Long-distance transmission is typically done with overhead lines at voltages of 115 to 1,200 kV. At extremely high voltages, more than 2,000 kV exists between conductor and ground, corona discharge losses are so large that they can offset the lower resistive losses in the line conductors. Measures to reduce corona losses include conductors having larger diameters; often hollow to save weight,or bundles of two or more conductors.

Factors affecting

Factors that affect the resistance, and thus loss, of conductors used in transmission and distribution lines include temperature, spiraling, and the skin effect. The resistance of a conductor increases with its temperature. Temperature changes in electric power lines can have a significant effect on power losses in the line. Spiraling, which refers to the increase in conductor resistance due to the way stranded conductors spiral about the center, also contributes to increases in conductor resistance. The skin effect causes the effective resistance of a conductor to increase at higher alternating current frequencies.

Transmission and distribution losses in the USA were estimated at 6.6% in 1997 and 6.5% in 2007. In general, losses are estimated from the discrepancy between power produced (as reported by power plants) and power sold to the end customers; the difference between what is produced and what is consumed constitute transmission and distribution losses, assuming no utility theft occurs.

As of 1980, the longest cost-effective distance for direct-current transmission was determined to be 7,000 km (4,300 mi). For alternating current it was 4,000 km (2,500 mi), though all transmission lines in use today are substantially shorter than this.

Inductance and capacitance

In any alternating current transmission line, the inductance and capacitance of the conductors can be significant. Currents that flow solely in 'reaction' to these properties of the circuit, (which together with the resistance define the impedance) constitute reactive power flow, which transmits no 'real' power to the load. These reactive currents, however, are very real and cause extra heating losses in the transmission circuit. The ratio of 'real' power (transmitted to the load) to 'apparent' power (sum of 'real' and 'reactive') is the power factor. As reactive current increases, the reactive power increases and the power factor decreases. For transmission systems with low power factor, losses are higher than for systems with high power factor. Utilities add capacitor banks, reactors and other components (such as phase-shifting transformers; static VAR compensators; and flexible AC transmission systems, FACTS) throughout the system to compensate for the reactive power flow and reduce the losses in power transmission and stabilize system voltages. These measures are collectively called 'reactive support'.

HYDRO PROJECT REPORT(THEORY ONLY)?

ABSTRACT

PAKISTAN is passing through serious energy crisis for a long time ,hydro share is less  towards generation side but controversially hydro energy can fulfill energy requirements wonderfully to do so there is need to be not selfished and proper management. Hydro power plants  convert potential energy of water into electricity. It is a clean source of energy. The water after generating electrical power is available for irrigation and other purposes. The first use of moving water to produce electricity was a waterwheel on the Fox River in Wisconsin in 1882. In this mini hydro power plant we produced electricity with the help of water which moves the TURBINE coupled with generator  to produce electricity

INTRODUCTION                            

Hydropower of recent era is an extremely flexible technology for power generation. Hydro reservoirs provide built-in energy storage, and the fast response time of hydropower enables it to be used to optimise electricity production across grids, meeting sudden fluctuations in demands.

However, large scale hydropower projects can be controversial because they affect water availability down stream, inundate valuable ecosystems and may require the relocations of populations. Despite being a mature technology, in comparison with other renewable energy sources, hydropower has still a significant potential. New plants can be developed and old ones upgraded, especially in terms of increasing efficiency and electricity production as well as environmental performance. In particular, the development of low-head or very low-head small hydro plants holds much promise.

A Small Hydro Power Plant (SHP) is not simply a reduced version of a large hydro plant. Small hydro plants generate electricity or mechanical power by converting the power available in flowing waters in rivers, canals and streams with a certain fall (termed the ‘head’) into electric energy at the lower end of the scheme, where the powerhouse is located. The power of the scheme is proportional to the flow and to the head. Small hydropower schemes are mainly run off-river with no need to create a reservoir. Because of this fact, small hydropower systems can be considered an environmentally friendly energy conversion option, since they do not interfere significantly with river flows and fit in well with the surroundings. The advantages of small hydropower plants are numerous and include grid stability, reduced land requirements, local and regional development and good opportunities for technologies export.

Even if there is no international consensus on the definition of SHP, a capacity of 10MW total is generally becoming accepted in Europe and is supported by the European Commission and the European Small Hydropower Association.

Construction and Working of Hydro Power Plant

In hydro power plant we use gravitational force of fluid water to run the turbine which is coupled with electric generator to produce electricity. This power plant plays an important role to protect our fossil fuel which is limited, because the generated electricity in hydro power station is the use of water which is renewable source of energy and available in lots of amount without any cost. Fundamental parts of hydro power plant are

a)         Area

b)         Dam

c)         Reservoir

d)         Penstock

e)         Turbine                       

f)         generators

 For construction of hydro power plant first we choose the area where the water is sufficient to reserve and no any crisis of water and suitable to build a dam, then we construct the dam. The main function of dam is to stop the flow of water and reserve the water in reservoir. Mainly dam is situated at a good height to increase the force of water. Reservoir stocks up lots of water which is employed to generate power by means of turbines. After that Penstock, the pipe which is connected between dam and turbine blades and most important purpose of the penstock is to enlarge the kinetic energy of water that’s why this pipe is made up of extremely well-built material which carry on the pressure of water. To control the pressure of water means increase or decrease water pressure whenever required, we use a valve. Storage tank comes in picture when the some reason the pressure of water in reservoir is decreases then we use storage tank it is directly connected to penstock and use only in emergency condition. After that we employ turbine and generator. Turbine is the main stuff, when water comes through the penstock with high kinetic energy and falls on turbine blades, turbine rotates at high speed. As we know that the turbine is an engine that transfers energy of fluid into mechanical energy which is coupled with generator and generator converts mechanical energy into electrical energy which we utilize at the end. In hydro power plant we also add switchgears and protections which control and protect the whole process inside the plant. The control equipments consists control circuits, control devices, warning, instrumentation etc and connect to main control board. After generating electricity at low voltage, we use step up transformer to enlarge the level of voltage (generally 132KV, 220KV, 400KV and above) as per our requirement. After that we transmit the electric power to the load center, and then we step down the voltage for industrial and large consumer and then again we step down the

voltage to distribute electricity at domestic level which we used at home.
This is the whole process of generating electricity by the means of hydro (hydro power plant) and then transmitting and distributing electricity.

                               

 CONCLUSION

Resulting output graph is exponentially decay. Different values of voltage are obtained and consequently current values are attained. It is obvious from the graph that voltage and current are inversely related with each other. 

 

   REFERENCES 

Ø  Electrical4u.com

Ø  Wikipedia

Easy and comprehensive description of voice control and remote control wheel chair project?

Introduction

Voice control and remote control wheel chair is such a sort of project in which wheel chair is controlled with respect to voice and remote. Here geetech speech recognition module is used for wheel chair controlling by voice. And double pole double throw switch(DPDT switch) is used for remote control purposes. A wheel chair will be controlled by geetech in left and right, forward and backward directions and stop too. The DPDT switch helps us controlling wheel chair in remote fashion manually.(coming soon)

Required Components:

·        Geetech speech recognition

·        LM293D motor driver

·        Aurdino UNO

·        DC motors

·        Resistors

·        Wheel chair structure

·        DPDT Switches

·        Batteries

·        Voltage regulator

·        2 core shield wire

Block diagram 

Proposed methodology:

Methodology that we are going to suppose in voice control and remote control project is of special interest and informative too. Geetech that is voice recognition module synchronized with arduino. Voice control module has three groups but we are using only one group. One group contains a proper functionality by which we synchronize geetech module with arduino in such a way that left and right, forward and backward directions movement is achieved according to instructions provided to arduino of our choice and furthermore we can stop smart wheelchair by doing programming in arduino. The synchronized connection between geetech module and arduino becomes possible by mutual interlinking transmitters and receivers of both arduino and voice recognition module. Two motors connected to the arduino pins get arduino instructions in the form of left and right,forward and backward directions and stop mode and work according to these instructions  properly.

The second part is remote control that is performed using two double pole double throw switch(DPDT switch).This switch comprises six points or six pinholes that are directly connected to the motors and turning of of the switch helps us controlling the motor using  remote manually. Furthermore,two wire shield wire is used for efficient connections and performance.

Types of Wheelchair

There are a wide variety of types of wheelchair, differing by propulsion method, mechanisms of control, and technology used. Some wheelchairs are designed for general everyday use, others for single activities, or to address specific access needs. Innovation within the wheelchair industry is relatively common, but many innovations ultimately fall by the wayside, either from over-specialization, or from failing to come to market at an accessible price-point. The iBot is perhaps the best known example of this in recent years.

Manual self-propelled wheelchairs

A self-propelled manual wheelchair incorporates a frame, seat, one or two footplates (footrests) and four wheels: usually two caster wheels at the front and two large wheels at the back. There will generally also be a separate seat cushion. The larger rear wheels usually have push-rims of slightly smaller diameter projecting just beyond the tyre; these allow the user to manouevre the chair by pushing on them without requiring them to grasp the tyres. Manual wheelchairs generally have brakes that bear on the tyres of the rear wheels, however these are solely a parking brake and in-motion braking is provided by the user's palms bearing directly on the push-rims. As this causes friction and heat build-up, particularly on long downslopes, many wheelchair users will choose to wear padded wheelchair gloves. Manual wheelchairs often have two push handles at the upper rear of the frame to allow for manual propulsion by a second person, however many active wheelchair users will remove these to prevent unwanted pushing from people who believe they are being helpful.

Everyday manual wheelchairs come in two major varieties, folding or rigid. Folding chairs are generally low-end designs, whose predominant advantage is being able to fold, generally by bringing the two sides together. However this is largely an advantage for part-time users who may need to store the wheelchair more often than use it. Rigid wheelchairs, which are increasingly preferred by full-time and active users, have permanently welded joints and many fewer moving parts. This reduces the energy required to push the chair by eliminating many points where the chair would flex and absorb energy as it moves. Welded rather than folding joints also reduce the overall weight of the chair. Rigid chairs typically feature instant-release rear wheels and backrests that fold down flat, allowing the user to dismantle the chair quickly for storage in a car. A few wheelchairs attempt to combine the features of both designs by providing a fold-to-rigid mechanism in which the joints are mechanically locked when the wheelchair is in use.

Many rigid models are now made with ultralight materials such as aircraft-grade aluminium and titanium, and wheelchairs of composite materials such as carbon-fibre have started to appear. Ultralightweight rigid wheelchairs are commonly known as 'active user chairs' as they are ideally suited to independent use. Another innovation in rigid chair design is the installation of shock absorbers, such as Frog Legs, which cushion the bumps over which the chair rolls. These shock absorbers may be added to the front wheels, to the rear wheels, or both. Rigid chairs also have the option for their rear wheels to have a camber, or tilt, which angles the tops of the wheels in toward the chair. This allows for more mechanically efficient propulsion by the user and also makes it easier to hold a straight line while moving across a slope. Sport wheelchairs often have large camber angles to improve stability.

Rigid-framed chairs are generally made to measure, to suit both the specific size of the user and their needs and preferences around areas such as the "tippyness" of the chair - its stability around the rear axle. Experienced users with sufficient upper-body strength can generally balance the chair on its rear wheels, a "wheelie", and the "tippyness" of the chair controls the ease with which this can be initiated. The wheelie allows an independent wheelchair user to climb and descend curbs and move more easily over small obstacles and irregular ground such as cobbles.

The rear wheels of self-propelled wheelchairs typically range from 20–24 inches (51–61 cm)in diameter, and commonly resemble bicycle wheels. Wheels are rubber-tyred and may be solid, pneumatic or gel-filled. The wheels of folding chairs may be permanently attached, but those for rigid chairs are commonly fitted with quick-release axles activated by depressing a button at the centre of the wheel.

All major varieties of wheelchair can be highly customised for the user's needs. Such customisations may encompass the seat dimensions, height, seat angle, footplates, leg rests, front caster outriggers, adjustable backrests and controls. Various optional accessories are available, such as anti-tip bars or wheels, safety belts, adjustable backrests, tilt and/or recline features, extra support for limbs or head and neck, holders for crutches, walkers or oxygen tanks, drink holders, and mud and wheel-guards as clothing protectors.

Light weight and high cost are related in the manual wheelchair market. At the low-cost end, heavy, folding steel chairs with sling seats and little adaptability dominate. Users may be temporarily disabled, or using such a chair as a loaner, or simply unable to afford better. These chairs are common as "loaners" at large facilities such as airports, amusement parks and shopping centers. A slightly higher price band sees the same folding design produced in aluminium. Price typically then jumps from low to mid hundreds of pounds/dollars/euros to a four figure price range, with individually custom manufactured lightweight chairs with more options. The high end of the market contains ultra-light models, extensive seating options and accessories, all-terrain features, and so forth. The most expensive manual chairs may rival the cost of a small car.

Manual attendant-propelled wheelchairs

An attendant-propelled wheelchair is generally similar to a self-propelled manual wheelchair, but with small diameter wheels at both front and rear. The chair is manoeuvred and controlled by a person standing at the rear and pushing on handles incorporated into the frame. Braking is supplied directly by the attendant who will usually also be provided with a foot- or hand-operated parking brake.

These chairs are common in institutional settings and as loaner-chairs in large public venues. They are usually constructed from steel as light weight is less of a concern when the user is not required to self-propel.

Specially designed transfer chairs are now required features at airports in much of the developed world in order to allow access down narrow airliner aisles and facilitate the transfer of wheelchair-using passengers to and from their seats on the aircraft.

Powered wheelchairs

Main article: Motorized wheelchair

An electric-powered wheelchair, commonly called a "powerchair" is a wheelchair which additionally incorporates batteries and electric motors into the frame and that is controlled by either the user or an attendant, most commonly via a small joystick mounted on the armrest, or on the upper rear of the frame. For users who cannot manage a manual joystick, headswitches, chin-operated joysticks, sip-and-puff controllers or other specialist controls may allow independent operation of the wheelchair. Ranges of over 10 miles/15 km are commonly available from standard batteries.

Powerchairs are commonly divided by their access capabilities. An indoor-chair may only reliably be able to cross completely flat surfaces, limiting them to household use. An indoor-outdoor chair is less limited, but may have restricted range or ability to deal with slopes or uneven surfaces. An outdoor chair is more capable, but will still have a very restricted ability to deal with rough terrain. A very few specialist designs offer a true cross-country capability.

Powerchairs have access to the full range of wheelchair options, including ones which are difficult to provide in an unpowered manual chair, but have the disadvantage of significant extra weight. Where an ultra-lightweight manual chair may weigh under 10Kg, the largest outdoor power-chairs may weigh 200Kg or more.

Smaller power chairs often have four wheels, with front or rear wheel drive, but large outdoor designs commonly have six wheels, with small wheels at front and rear and somewhat larger powered wheels in the centre.

A power-assisted wheelchair is a recent development that uses the frame & seating of a typical rigid manual chair while replacing the standard rear wheels with wheels of similar size which incorporate batteries and battery-powered motors in the hubs. A floating rim design senses the pressure applied by the users push & activates the motors proportionately to provide a power assist. This results in the convenience, and small size of a manual chair while providing motorised assistance for rough/uneven terrain & steep slopes that would otherwise be difficult or impossible to navigate, especially by those with limited upper-body function. As the wheels necessarily come at a weight penalty it is often possible to exchange them with standard wheels to match the capabilities of the wheelchair to the current activity.

Mobility scooters

Mobility scooters share some features with powerchairs, but primarily address a different market segment, people with a limited ability to walk, but who might not otherwise consider themselves disabled. Smaller mobility scooters are typically three wheeled, with a base on which is mounted a basic seat at the rear, with a control tiller at the front. Larger scooters are frequently four-wheeled, with a much more substantial seat.

Opinions are often polarized as to whether mobility scooters should be considered wheelchairs or not, and negative stereotyping of scootr users is worse than for manual or powerchair users. Some commercial organisations draw a distinction between powerchairs and scooters when making access provisions due to a lack of clarity in the law as to whether scooters fall under the same equality legislation as wheelchairs.

Single-arm drive wheelchairs

One-arm or single arm drive enables a user to self-propel a manual wheelchair using only a single arm. The large wheel on the same side as the arm to be used is fitted with two concentric handrims, one of smaller diameter than the other. On most models the outer, smaller rim, is connected to the wheel on the opposite side by an inner concentric axle. When both handrims are grasped together, the chair may be propelled forward or backward in a straight line. When either handrim is moved independently, only a single wheel is used and the chair will turn left or right in response to the handrim used. Some wheelchairs, designed for use by hemiplegics, provide a similar function by linking both wheels rigidly together and using one of the footplates to control steering via a linkage to the front caster.

Reclining wheelchairs

Reclining or tilt-in-space wheelchairs have seating surfaces which can be tilted to various angles. The original concept was developed by an orthotist, Hugh Barclay, who worked with disabled children and observed that postural deformities such as scoliosis could be supported or partially corrected by allowing the wheelchair user to relax in a tilted position. The feature is also of value to users who are unable to sit upright for extended periods for pain or other reasons. Various designs are now available and wheelchairs with the feature may either tilt the seat-back and legrests in relation to the seat, or may tilt the entire back, seat and legrest as one, depending on the need of the user.

Standing wheelchairs

A standing wheelchair is one that supports the user in a nearly standing position. They can be used as both a wheelchair and a standing frame, allowing the user to sit or stand in the wheelchair as they wish. Some versions are entirely manual, others have powered stand on an otherwise manual chair, while others have full power, tilt, recline and variations of powered stand functions available. The benefits of such a device include, but are not limited to: aiding independence and productivity, raising self-esteem and psychological well-being, heightening social status, extending access, relief of pressure, reduction of pressure sores, improved functional reach, improved respiration, reduced occurrence of UTI, improved flexibility, help in maintaining bone mineral density, improved passive range motion, reduction in abnormal muscle tone and spasticity, and skeletal deformities. Other wheelchairs provide some of the same benefits by raising the entire seat to lift the user to standing height.

Sports wheelchairs

A modern racing wheelchair

A range of disabled sports have been developed for disabled athletes, including basketball, rugby, tennis, racing and dancing. The wheelchairs used for each sport have evolved to suit the specific needs of that sport and often no longer resemble their everyday cousins. They are usually non-folding (in order to increase rigidity), with a pronounced negative camber for the wheels (which provides stability and is helpful for making sharp turns), and often are made of composite, lightweight materials. Even seating position may be radically different, with racing wheelchairs generally used in a kneeling position. Sport wheelchairs are rarely suited for everyday use, and are often a 'second' chair specifically for sport use, although some users prefer the sport options for everyday. Some disabled people, for instance lower-limb amputees, may use a wheelchair for sports, but not for everyday activities.

Wheelchair stretchers

Wheelchair stretchers are a variant of wheeled stretchers/gurneys that can accommodate a sitting patient, or be adjusted to lie flat to help in the lateral (or supine) transfer of a patient from a bed to the chair or back. Once transferred, the stretcher can be adjusted to allow the patient to assume a sitting position.

All-terrain wheelchairs

All-terrain wheelchairs can allow users to access terrain otherwise completely inaccessible to a wheelchair user. Two different formats have been developed. One hybridises wheelchair and mountain bike technology, generally taking the form of a frame within which the user sits and with four mountain bike wheels at the corners. In general there are no push-rims and propulsion/braking is by pushing directly on the tyres.

A more common variant is the beach wheelchair which can allow better mobility on beach sand, including in the water, on uneven terrain, and even on snow. The common adaptation among the different designs is that they have extra-wide balloon wheels or tires, to increase stability and decrease ground pressure on uneven or unsteady terrain. Different models are available, both manual and battery-driven. In some countries in Europe, where accessible tourism is well established, many beaches have wheelchairs of this type available for loan/hire.

iBot

iBot was a radical powerchair developed by Dean Kamen to incorporate gyroscopic and active control technology, enabling the chair to balance and run on only two of its four wheels on some surfaces, thus raising the user to standing height. It was also able to climb stairs by leveraging the standing feature. The popular Segway Personal Transporter is a mobility device that was a direct outgrowth of the development of the iBOT wheelchair. The Segway, which is basically an iBOT with two wheels removed, was developed explicitly to increase the number of units produced and take advantage of the economies of scale to attempt to make the iBOT affordable to wheelchair users. While popular in concept, the $25,000 iBot, which was developed as a joint venture between Johnson and Johnson's Independence Technology and Kamen's DEKA Research, was priced at too high a price point to sustain the needed production and was discontinued in January 2009.

Smart wheelchairs

A smart wheelchair is any powerchair using a control system to augment or replace user control. Its purpose is to reduce or eliminate the user's task of driving a powerchair. Usually, a smart wheelchair is controlled via a computer, has a suite of sensors and applies techniques in mobile robotics, but this is not necessary. The interface may consist of a conventional wheelchair joystick, a "sip-and-puff" device or a touch-sensitive display. This differs from a conventional powerchair, in which the user exerts manual control over speed and direction without intervention by the wheelchair's control system.

Smart wheelchairs are designed for a variety of user types. Some are designed for users with cognitive impairments, such as dementia, these typically apply collision-avoidance techniques to ensure that users do not accidentally select a drive command that results in a collision. Othersfocus on users living with severe motor disabilities, such as cerebral palsy, or with quadriplegia, and the role of the smart wheelchair is to interpret small muscular activations as high-level commands and execute them. Such wheelchairs typically employ techniques from artificial intelligence, such as path-planning.Courtesy of wikipedia...