10-04-2017, 08:57 PM
Axial-Field Electrical Machines
Introduction
Axial-field electrical machines offer an alternative to the conventional machines. In the axial-field machine, the air gap flux is axial in direction and the active current carrying conductors are radially positioned. This paper presents the design characteristics, special features, manufacturing aspects and potential applications for axial-field electrical machines. The experimental from several prototypes, including d.c. machines, synchronous machines and single-phase machines are given.
The special features of the axial-field machine, such as its planar and adjustable air gap, flat shape, ease of diversification, etc., enable axial-fled machines to have distinct advantages over conventional machines in certain applications, especially in special purpose applications. conventional radial field machines. The axial field electrical machines described in this paper are particularly suitable for d.c and synchronous machines where the double air gaps present no difficulties since these machines normally require fairly large air gaps to reduce the effect of armature reaction. One of the major objections to the use of AFMs lies in the difficulty on cutting the slots in their laminated cores..
Brushless Servomotor
Brushless Servomotor
Introduction
A Brushless Servomotor has been developed by using interdisciplinary mechatronics engineering. A mechanical switching device (commutator) is replaced by electronic circuits and controllers resulting in maintenance free and high performance servo drive. The brushless servomotor is an ac motor, in all respects and is in fact called the ac servomotor. Combined with a dedicated control device, the performance of the brushless servomotor is found to be equal to the performance of the high performance dc servo motor. In dc motor when the current flows in the electrical conductor, after passing through the brushes and the commutator in the magnetic field generated by permanent magnets N and S, torque is generated.
For getting a stable torque proportional to current, the line of magnetic force should intersect the direction of current at right angles in a dc motor. This is enabled by the use of rectifiers (a commutator and brushes).The brushless servomotor lacks the rectifiers that the de motor has, and has a device for making the current flow to fit the rotor position by controlling the power source. The increasing trend and need towards automated factories and sophisticated robotics would definitely make the use of servomotors more widespread..
Contactless Energy Transfer System
Contactless Energy Transfer System
Introduction
Most mains operated equipment in use today is connected to the supply via plugs and sockets. These are generally acceptable in benign environments but can be unsafe or have limited life in the presence of moisture. In explosive atmospheres and in undersea applications special connectors must be used.
This paper describes a technique, the Contactless Energy Transfer System (CETS), by which electrical energy maybe transmitted, without electrical connections or physical contact, through non-magnetic media of low conductivity. CETS, which has been used to transfer upto 5KWs across a 10mm gap, employs high frequency magnetic coupling and enables plug in power connections to be made in wet or hazardous environmental conditions without the risk of electric shock, short-circuiting or sparking. Energy may be transmitted without the necessity for accurately manufactured plug and socket mechanisms and may be transmitted from source to load even when there is a relative motion. Load source voltage matching may be made inherent to the system
Super Conducting Generator
Super Conducting Generator
Introduction
The superconducting generator using super conductors in field winding is superior to conventional generator in terms of power system stability, generator efficiency, generator dimensions and weight. They have been expected as a key generator technology to realize large capacity more them 1GVA.. Recently for then advantages are pointed out compared to conventional generator like small internal impedance that is effective to make system voltages in deregulated power system. These technical merits have pushed the development of superconducting generator in Japan, US, Germany and other countries.
This paper covers the structural details of rotor and stator, the working and the cooling system for super conducting field windings. Also the main features and research and development on super conducing generator are covered briefly. . Fundamental technology for higher density and larger capacity is now under research. It is expected that superconducting generators becomes superior to conventional generators from economical and performance point of view. Superconducting generators are useful for solving problems appeared in power system and they are expected to the major source of electrical power in the coming decades..
Low voltage differential signaling (LVDS)
Low voltage differential signaling (LVDS)
Introduction
Low voltage differential signaling, or LVDS, is an electrical signaling system that can run at very high speeds over cheap, twisted-pair copper cables. It was introduced in 1994, and has since become very popular in computers, where it forms part of very high-speed networks and computer buses. LVDS uses the difference in voltage between two wires to signal information.
The transmitter injects a small current, nominally 3.5 milliamperes, into one wire or the other, depending on the logic level to be sent. The current passes through a resistor of about 100 to 120 ohms (matched to the characteristic impedance of the cable) at the receiving end, then returns in the opposite direction along the other wire. From Ohm's law, the voltage difference across the resistor is therefore about 350 millivolts. The receiver senses the polarity of this voltage to determine the logic level. (This is a type of current loop signaling). .
Solar Hybrid PVT Systems
Solar Hybrid PVT Systems
Introduction
The tending extinction of fossil fuels has already created an awareness to look for alternative sources of energy of which solar is most promising in a topical country like ours , where it is available in abundance .
The efforts are being made to utilize solar energy in building sector to fulfill the thermal as well as electrical requirements. Various thermal systems have being developed and commercialized for space and water heating . Work is being done on projects to generate electricity through photovoltaic convert ion. The efficiency of the photovoltaic conversion is inversely proportional to the temperature.
When the temperature rises, there are occasions when the PV conversion is very adversely affected leading to the system failure. The basic idea in the development of hybrid panel is to utilize the radiations not used for photovoltaic conversion, directly for thermal purposes and all radiations falling on the photovoltaic cell, which are partially used for PV conversion and the remaining heats up the cells. A suitable heat exchanger has been designed & attached to the photovoltaic panel to extract the heat from hybrid panel to give
1. Hot water for use in buildings
2. Increased PV efficiency.
This paper deals with the results obtained from glass to glass-laminated ONGC type PV module and the initial performance evaluation test of modified module along with its instrumentation.
Conditional Monitoring
Conditional Monitoring
Introduction
Transformers are a large part of the component structure of the electricity system. Knowing the condition is essential to meeting the goals of maximizing return on investment and lowering total cost associated with transformer operation.
In order to reconcile both decreasing maintenance spending and reliable service, condition based maintenance (CBM) is often proposed. The successful application of CBM lies in obtaining information transformers, so that, on the one hand, a critical condition will be noted early enough to take measures and on the other hand, so that only minimal maintenance is being applied to transformers still in good condition.
The paper covers the following areas.
General aspects of aging in transformers.
An overview of condition monitoring methodology with partial discharge patterns in focus.
Partial discharge measurement and diagnostics on power transformer using a multi channel digital PD detector.
Optimum VAR Control
Optimum VAR Control
Introduction
A complex method for the optimum VAR control of radial primary power distribution networks dealing with the proper selection and installation of shunt capacitors is developed here. The problem is examined both on an annual and a long-term basis.
First objective functions and relative algorithms, which determine the kind, the size, the minimum numbers the locations and the adjustments of the possibly installed standard capacitors are developed. Then all these are embodied in a complex software package, which examines all the technically acceptable VAR control solutions.
It compares them economically and finally proposes the more profitable.In this, a complex method for the optimum VAR control of a radial primary distribution network with capacitors is developed. The problem is examined both for constant and growing annual peak load buy developing relative software packages. Realistic data of the examined networks such as lateral branches, conductor sizes, load distribution and variation are taken into account. The target in every case is the determination of the kind, size, minimum number, location and possible adjustments of standard capacitors which effect the techno economically var control. This is achieved by utilizing previous considerable methods dealing with the examined problem which however are adapted to new objective functions and they are modified so as to over come their weaknesses and to optimize the necessary computing time..
The Global Voltage Regulation
The Global Voltage Regulation
Introduction
Based on closed form expressions for the power frequency voltages and currents in a typical distribution network, the voltage regulation VR at any time point during the day could be evaluated. It will depend primarily on the network configuration, the daily load curve, the load density and its power factor as well as level of the reactive power compensation.
The computed at a certain time t can give a useful indicator for the voltage constancy over the network at that time point. The concept of Global Voltage Regulation is introduced. The GVR is defined as the root mean square value of the voltage regulation over the daytime as t varies from 0 to 24 h. Accordingly , it takes into account the effect of both the geometrical dimensions of the distribution network and the daily temporal variation of the voltage regulation .
The theoretical value GVR =0 corresponds to the ideal case in which the voltage is constant at all nodes ,all the time. Hence GVR can be considered as a representative figure of merit describing the supply quality regarding the voltage values prevailing at the different network nodes, allover the day. The paper also addresses the identification of the optimal level of reactive power compensation (K) that will lead to the least possible GVR. Moreover the impact of both the network and load parameters on the optimal value of K is investigated..
Synchronous Voltage Source
Synchronous Voltage Source
Introduction
The synchronous voltage source is implemented by a multi-pulse inverter using gate turnoff (GTO) thyristors . It is capable of generating internally the reactive power necessary for network compensation, and is also able to interface with an appropriate energy storage device to negotiate real power exchange with the ac system. The paper develops a of power flow control using solid - state synchronous voltage sources for shunt compensation, series compensation , and phase angle control .
It also describes the unified powerflow controller that is able to control concurrently or selectively all three network parameters(voltage, impedance, angle) determining power transmission. compensation method of employing thyristor switched capacitors and reactors shows its superior performance, uniform applicability, smaller physical size, and lower overall cost. There are clear indications that solid-state synchronous voltage sources represent the next technology for ac transmission system compensation and power flow control.
This technology offers operating features, functional performance, and application flexibility unattainable by the presently used circuit arrangements. The synchronous voltage source can be considered an ideal 60 Hz generator that has no inertia and produces an almost sinusoidal output voltage with independently variable amplitude and phase angle, thus facilitating rapid, decoupled controls for reactive and real power exchange. It can be used uniformly to control transmission line voltage, impedance, and angle by providing reactive shunt compensation, series compensation, and phase-shifting.
Gas Insulated Substations
Gas Insulated Substations
Introduction
SF6 Gas insulated Substations (GIS) are preferred for voltage ratings of 72.5KV, 145KV, 245KV, 420KV and above. In such a situation, the various equipments like circuit breakers, busbars, isolators, and load break switches; current transformers, voltage transformers, earthing switches etc. are housed in metal enclosed modules filled with SF6 gas.
The SF6 gas provides the phase to ground insulation. As the dielectric strength of SF6 gas is higher than the air, the clearances required are smaller. Hence, the overall size of each equipment and the complete substation is reduced to about 10% of conventional air insulated substations. As a rule GIS are installed indoor. However outdoor GIS have also been installed earlier.
The various modules of GIS are factory assembled and are filled with SF6 gas at a pressure of about 3 Kg/ cm2. Thereafter they are taken to site for final assembly. Such substations are compact and can be installed conveniently on any floor of a multi - storied building or in an underground substation.As the units are factory assembled, the installation time is substantially reduced. Such installation are preferred in cosmopolitan cities, industrial townships, etc. where cost of land is very high and higher cost of SF6 insulated switch gear (GIS) is justified by saving due to reduction in floor area requirement. They are also preferred in heavily polluted areas where dust, chemical fumes and salt layers can cause frequent flashovers in conventional outdoor air-insulated substations. The GIS has monitoring system.
The gas density in each compartment is monitored. If pressured drops slightly, the gas is automatically tapped up. With further gas leakage, the low-pressure alarm is sounded or automatic tripping or lock out occurs. By this method we can save the space required for the substation to build up. This means that gas-insulated substation can be built in any metropolitan city. Many experiments are going on the use of SF6 gas
Superconductivity
Superconductivity
Introduction
SUPERCONDUCTIVITY is the ability of certain materials to conduct electric current with no resistance and extremely low losses. This ability to carry large amounts of currents can be applied to electric power devices such as motors and generators and to electricity transmission in power lines.
For example, superconductors can carry as much as 100 times the electricity ordinary copper or aluminium wires of same size.Scientists had been intrigued with the concept of superconductivity since its discovery in the early 1900 s, but the extreme low temperature the phenomenon required was a barrier to practical and low cost application.
This all changed in 1986 when a new class of ceramic super conductors were discovered that SUPERCONDUCTED at higher temperatures. The science of high temperature superconductivity (HTS) was born, and along with it came the prospect for an elegant technology that promises to supercharge the way energy is generated, delivered and used.At the heart of high temperature superconductivity lies a promise for the near future.
A promise for transmitting and using electricity with near perfect efficiency and much higher capacity, besides all this it also has a wide range of application like MRI scanning, maglev trains etc. This seminar shall discuss on the concepts of superconductivity, its classifications, its various properties and its applications.
We have completed the first electrical century ushered in by Thomas Edison . We are now entering a second electrical century, ushered in by High Temperature Superconductivity. .
Automatic Solar Tracker
Automatic Solar Tracker
Introduction
A new control scheme for a single phase diode clamped rectifier is proposed to achieve a unity power factor, balanced neutral point voltage and constant DC-bus voltage. Four power switches are used in the rectifier to generate a three-level PWM wave form on the rectifier terminal voltage.
The line current command is derived from a DC-link voltage regulator and an output power estimator. The hysteresis current Controller is used to track the line current command. To balance the neutral-point voltage, a capacitor voltage compensator is employed. The main advantages of using a three-level instead of a two-level PWM scheme are that the blocking voltage of each power switch is clamped to half the DC-bus voltage (if the off state resistance of power switches is equal),and the voltage harmonic on the AC side of rectifier is reduced.
A novel single phase neutral point diode clamped rectifier has been proposed to achieve high power factor, low current distortion, low peak factor, and stable capacitor voltages. The proposed rectifier can be controlled to operate in two- or-three level PWM.
Based on the model analysis, the switching signals of the power switches can be derived from the measured line current error and the mains voltage. Experimental results show a good line current waveform with almost unity power factor and low current harmonics to meet the requirements of IEC 1000-3-2 class A. The transient response due to load change is about one cycle and voltage drop is about 5V. According to measured results the proposed rectifier has the properties of high power factor, low current distortion and fast dynamic response, based on the proposed control algorithm.
Automatic Solar Tracker
Automatic Solar Tracker
Introduction
A new control scheme for a single phase diode clamped rectifier is proposed to achieve a unity power factor, balanced neutral point voltage and constant DC-bus voltage. Four power switches are used in the rectifier to generate a three-level PWM wave form on the rectifier terminal voltage. The line current command is derived from a DC-link voltage regulator and an output power estimator. The hysteresis current Controller is used to track the line current command. To balance the neutral-point voltage, a capacitor voltage compensator is employed. The main advantages of using a three-level instead of a two-level PWM scheme are that the blocking voltage of each power switch is clamped to half the DC-bus voltage (if the off state resistance of power switches is equal),and the voltage harmonic on the AC side of rectifier is reduced.
A novel single phase neutral point diode clamped rectifier has been proposed to achieve high power factor, low current distortion, low peak factor, and stable capacitor voltages. The proposed rectifier can be controlled to operate in two- or-three level PWM.
Based on the model analysis, the switching signals of the power switches can be derived from the measured line current error and the mains voltage. Experimental results show a good line current waveform with almost unity power factor and low current harmonics to meet the requirements of IEC 1000-3-2 class A. The transient response due to load change is about one cycle and voltage drop is about 5V. According to measured results the proposed rectifier has the properties of high power factor, low current distortion and fast dynamic response, based on the proposed control algorithm.
Introduction
Axial-field electrical machines offer an alternative to the conventional machines. In the axial-field machine, the air gap flux is axial in direction and the active current carrying conductors are radially positioned. This paper presents the design characteristics, special features, manufacturing aspects and potential applications for axial-field electrical machines. The experimental from several prototypes, including d.c. machines, synchronous machines and single-phase machines are given.
The special features of the axial-field machine, such as its planar and adjustable air gap, flat shape, ease of diversification, etc., enable axial-fled machines to have distinct advantages over conventional machines in certain applications, especially in special purpose applications. conventional radial field machines. The axial field electrical machines described in this paper are particularly suitable for d.c and synchronous machines where the double air gaps present no difficulties since these machines normally require fairly large air gaps to reduce the effect of armature reaction. One of the major objections to the use of AFMs lies in the difficulty on cutting the slots in their laminated cores..
Brushless Servomotor
Brushless Servomotor
Introduction
A Brushless Servomotor has been developed by using interdisciplinary mechatronics engineering. A mechanical switching device (commutator) is replaced by electronic circuits and controllers resulting in maintenance free and high performance servo drive. The brushless servomotor is an ac motor, in all respects and is in fact called the ac servomotor. Combined with a dedicated control device, the performance of the brushless servomotor is found to be equal to the performance of the high performance dc servo motor. In dc motor when the current flows in the electrical conductor, after passing through the brushes and the commutator in the magnetic field generated by permanent magnets N and S, torque is generated.
For getting a stable torque proportional to current, the line of magnetic force should intersect the direction of current at right angles in a dc motor. This is enabled by the use of rectifiers (a commutator and brushes).The brushless servomotor lacks the rectifiers that the de motor has, and has a device for making the current flow to fit the rotor position by controlling the power source. The increasing trend and need towards automated factories and sophisticated robotics would definitely make the use of servomotors more widespread..
Contactless Energy Transfer System
Contactless Energy Transfer System
Introduction
Most mains operated equipment in use today is connected to the supply via plugs and sockets. These are generally acceptable in benign environments but can be unsafe or have limited life in the presence of moisture. In explosive atmospheres and in undersea applications special connectors must be used.
This paper describes a technique, the Contactless Energy Transfer System (CETS), by which electrical energy maybe transmitted, without electrical connections or physical contact, through non-magnetic media of low conductivity. CETS, which has been used to transfer upto 5KWs across a 10mm gap, employs high frequency magnetic coupling and enables plug in power connections to be made in wet or hazardous environmental conditions without the risk of electric shock, short-circuiting or sparking. Energy may be transmitted without the necessity for accurately manufactured plug and socket mechanisms and may be transmitted from source to load even when there is a relative motion. Load source voltage matching may be made inherent to the system
Super Conducting Generator
Super Conducting Generator
Introduction
The superconducting generator using super conductors in field winding is superior to conventional generator in terms of power system stability, generator efficiency, generator dimensions and weight. They have been expected as a key generator technology to realize large capacity more them 1GVA.. Recently for then advantages are pointed out compared to conventional generator like small internal impedance that is effective to make system voltages in deregulated power system. These technical merits have pushed the development of superconducting generator in Japan, US, Germany and other countries.
This paper covers the structural details of rotor and stator, the working and the cooling system for super conducting field windings. Also the main features and research and development on super conducing generator are covered briefly. . Fundamental technology for higher density and larger capacity is now under research. It is expected that superconducting generators becomes superior to conventional generators from economical and performance point of view. Superconducting generators are useful for solving problems appeared in power system and they are expected to the major source of electrical power in the coming decades..
Low voltage differential signaling (LVDS)
Low voltage differential signaling (LVDS)
Introduction
Low voltage differential signaling, or LVDS, is an electrical signaling system that can run at very high speeds over cheap, twisted-pair copper cables. It was introduced in 1994, and has since become very popular in computers, where it forms part of very high-speed networks and computer buses. LVDS uses the difference in voltage between two wires to signal information.
The transmitter injects a small current, nominally 3.5 milliamperes, into one wire or the other, depending on the logic level to be sent. The current passes through a resistor of about 100 to 120 ohms (matched to the characteristic impedance of the cable) at the receiving end, then returns in the opposite direction along the other wire. From Ohm's law, the voltage difference across the resistor is therefore about 350 millivolts. The receiver senses the polarity of this voltage to determine the logic level. (This is a type of current loop signaling). .
Solar Hybrid PVT Systems
Solar Hybrid PVT Systems
Introduction
The tending extinction of fossil fuels has already created an awareness to look for alternative sources of energy of which solar is most promising in a topical country like ours , where it is available in abundance .
The efforts are being made to utilize solar energy in building sector to fulfill the thermal as well as electrical requirements. Various thermal systems have being developed and commercialized for space and water heating . Work is being done on projects to generate electricity through photovoltaic convert ion. The efficiency of the photovoltaic conversion is inversely proportional to the temperature.
When the temperature rises, there are occasions when the PV conversion is very adversely affected leading to the system failure. The basic idea in the development of hybrid panel is to utilize the radiations not used for photovoltaic conversion, directly for thermal purposes and all radiations falling on the photovoltaic cell, which are partially used for PV conversion and the remaining heats up the cells. A suitable heat exchanger has been designed & attached to the photovoltaic panel to extract the heat from hybrid panel to give
1. Hot water for use in buildings
2. Increased PV efficiency.
This paper deals with the results obtained from glass to glass-laminated ONGC type PV module and the initial performance evaluation test of modified module along with its instrumentation.
Conditional Monitoring
Conditional Monitoring
Introduction
Transformers are a large part of the component structure of the electricity system. Knowing the condition is essential to meeting the goals of maximizing return on investment and lowering total cost associated with transformer operation.
In order to reconcile both decreasing maintenance spending and reliable service, condition based maintenance (CBM) is often proposed. The successful application of CBM lies in obtaining information transformers, so that, on the one hand, a critical condition will be noted early enough to take measures and on the other hand, so that only minimal maintenance is being applied to transformers still in good condition.
The paper covers the following areas.
General aspects of aging in transformers.
An overview of condition monitoring methodology with partial discharge patterns in focus.
Partial discharge measurement and diagnostics on power transformer using a multi channel digital PD detector.
Optimum VAR Control
Optimum VAR Control
Introduction
A complex method for the optimum VAR control of radial primary power distribution networks dealing with the proper selection and installation of shunt capacitors is developed here. The problem is examined both on an annual and a long-term basis.
First objective functions and relative algorithms, which determine the kind, the size, the minimum numbers the locations and the adjustments of the possibly installed standard capacitors are developed. Then all these are embodied in a complex software package, which examines all the technically acceptable VAR control solutions.
It compares them economically and finally proposes the more profitable.In this, a complex method for the optimum VAR control of a radial primary distribution network with capacitors is developed. The problem is examined both for constant and growing annual peak load buy developing relative software packages. Realistic data of the examined networks such as lateral branches, conductor sizes, load distribution and variation are taken into account. The target in every case is the determination of the kind, size, minimum number, location and possible adjustments of standard capacitors which effect the techno economically var control. This is achieved by utilizing previous considerable methods dealing with the examined problem which however are adapted to new objective functions and they are modified so as to over come their weaknesses and to optimize the necessary computing time..
The Global Voltage Regulation
The Global Voltage Regulation
Introduction
Based on closed form expressions for the power frequency voltages and currents in a typical distribution network, the voltage regulation VR at any time point during the day could be evaluated. It will depend primarily on the network configuration, the daily load curve, the load density and its power factor as well as level of the reactive power compensation.
The computed at a certain time t can give a useful indicator for the voltage constancy over the network at that time point. The concept of Global Voltage Regulation is introduced. The GVR is defined as the root mean square value of the voltage regulation over the daytime as t varies from 0 to 24 h. Accordingly , it takes into account the effect of both the geometrical dimensions of the distribution network and the daily temporal variation of the voltage regulation .
The theoretical value GVR =0 corresponds to the ideal case in which the voltage is constant at all nodes ,all the time. Hence GVR can be considered as a representative figure of merit describing the supply quality regarding the voltage values prevailing at the different network nodes, allover the day. The paper also addresses the identification of the optimal level of reactive power compensation (K) that will lead to the least possible GVR. Moreover the impact of both the network and load parameters on the optimal value of K is investigated..
Synchronous Voltage Source
Synchronous Voltage Source
Introduction
The synchronous voltage source is implemented by a multi-pulse inverter using gate turnoff (GTO) thyristors . It is capable of generating internally the reactive power necessary for network compensation, and is also able to interface with an appropriate energy storage device to negotiate real power exchange with the ac system. The paper develops a of power flow control using solid - state synchronous voltage sources for shunt compensation, series compensation , and phase angle control .
It also describes the unified powerflow controller that is able to control concurrently or selectively all three network parameters(voltage, impedance, angle) determining power transmission. compensation method of employing thyristor switched capacitors and reactors shows its superior performance, uniform applicability, smaller physical size, and lower overall cost. There are clear indications that solid-state synchronous voltage sources represent the next technology for ac transmission system compensation and power flow control.
This technology offers operating features, functional performance, and application flexibility unattainable by the presently used circuit arrangements. The synchronous voltage source can be considered an ideal 60 Hz generator that has no inertia and produces an almost sinusoidal output voltage with independently variable amplitude and phase angle, thus facilitating rapid, decoupled controls for reactive and real power exchange. It can be used uniformly to control transmission line voltage, impedance, and angle by providing reactive shunt compensation, series compensation, and phase-shifting.
Gas Insulated Substations
Gas Insulated Substations
Introduction
SF6 Gas insulated Substations (GIS) are preferred for voltage ratings of 72.5KV, 145KV, 245KV, 420KV and above. In such a situation, the various equipments like circuit breakers, busbars, isolators, and load break switches; current transformers, voltage transformers, earthing switches etc. are housed in metal enclosed modules filled with SF6 gas.
The SF6 gas provides the phase to ground insulation. As the dielectric strength of SF6 gas is higher than the air, the clearances required are smaller. Hence, the overall size of each equipment and the complete substation is reduced to about 10% of conventional air insulated substations. As a rule GIS are installed indoor. However outdoor GIS have also been installed earlier.
The various modules of GIS are factory assembled and are filled with SF6 gas at a pressure of about 3 Kg/ cm2. Thereafter they are taken to site for final assembly. Such substations are compact and can be installed conveniently on any floor of a multi - storied building or in an underground substation.As the units are factory assembled, the installation time is substantially reduced. Such installation are preferred in cosmopolitan cities, industrial townships, etc. where cost of land is very high and higher cost of SF6 insulated switch gear (GIS) is justified by saving due to reduction in floor area requirement. They are also preferred in heavily polluted areas where dust, chemical fumes and salt layers can cause frequent flashovers in conventional outdoor air-insulated substations. The GIS has monitoring system.
The gas density in each compartment is monitored. If pressured drops slightly, the gas is automatically tapped up. With further gas leakage, the low-pressure alarm is sounded or automatic tripping or lock out occurs. By this method we can save the space required for the substation to build up. This means that gas-insulated substation can be built in any metropolitan city. Many experiments are going on the use of SF6 gas
Superconductivity
Superconductivity
Introduction
SUPERCONDUCTIVITY is the ability of certain materials to conduct electric current with no resistance and extremely low losses. This ability to carry large amounts of currents can be applied to electric power devices such as motors and generators and to electricity transmission in power lines.
For example, superconductors can carry as much as 100 times the electricity ordinary copper or aluminium wires of same size.Scientists had been intrigued with the concept of superconductivity since its discovery in the early 1900 s, but the extreme low temperature the phenomenon required was a barrier to practical and low cost application.
This all changed in 1986 when a new class of ceramic super conductors were discovered that SUPERCONDUCTED at higher temperatures. The science of high temperature superconductivity (HTS) was born, and along with it came the prospect for an elegant technology that promises to supercharge the way energy is generated, delivered and used.At the heart of high temperature superconductivity lies a promise for the near future.
A promise for transmitting and using electricity with near perfect efficiency and much higher capacity, besides all this it also has a wide range of application like MRI scanning, maglev trains etc. This seminar shall discuss on the concepts of superconductivity, its classifications, its various properties and its applications.
We have completed the first electrical century ushered in by Thomas Edison . We are now entering a second electrical century, ushered in by High Temperature Superconductivity. .
Automatic Solar Tracker
Automatic Solar Tracker
Introduction
A new control scheme for a single phase diode clamped rectifier is proposed to achieve a unity power factor, balanced neutral point voltage and constant DC-bus voltage. Four power switches are used in the rectifier to generate a three-level PWM wave form on the rectifier terminal voltage.
The line current command is derived from a DC-link voltage regulator and an output power estimator. The hysteresis current Controller is used to track the line current command. To balance the neutral-point voltage, a capacitor voltage compensator is employed. The main advantages of using a three-level instead of a two-level PWM scheme are that the blocking voltage of each power switch is clamped to half the DC-bus voltage (if the off state resistance of power switches is equal),and the voltage harmonic on the AC side of rectifier is reduced.
A novel single phase neutral point diode clamped rectifier has been proposed to achieve high power factor, low current distortion, low peak factor, and stable capacitor voltages. The proposed rectifier can be controlled to operate in two- or-three level PWM.
Based on the model analysis, the switching signals of the power switches can be derived from the measured line current error and the mains voltage. Experimental results show a good line current waveform with almost unity power factor and low current harmonics to meet the requirements of IEC 1000-3-2 class A. The transient response due to load change is about one cycle and voltage drop is about 5V. According to measured results the proposed rectifier has the properties of high power factor, low current distortion and fast dynamic response, based on the proposed control algorithm.
Automatic Solar Tracker
Automatic Solar Tracker
Introduction
A new control scheme for a single phase diode clamped rectifier is proposed to achieve a unity power factor, balanced neutral point voltage and constant DC-bus voltage. Four power switches are used in the rectifier to generate a three-level PWM wave form on the rectifier terminal voltage. The line current command is derived from a DC-link voltage regulator and an output power estimator. The hysteresis current Controller is used to track the line current command. To balance the neutral-point voltage, a capacitor voltage compensator is employed. The main advantages of using a three-level instead of a two-level PWM scheme are that the blocking voltage of each power switch is clamped to half the DC-bus voltage (if the off state resistance of power switches is equal),and the voltage harmonic on the AC side of rectifier is reduced.
A novel single phase neutral point diode clamped rectifier has been proposed to achieve high power factor, low current distortion, low peak factor, and stable capacitor voltages. The proposed rectifier can be controlled to operate in two- or-three level PWM.
Based on the model analysis, the switching signals of the power switches can be derived from the measured line current error and the mains voltage. Experimental results show a good line current waveform with almost unity power factor and low current harmonics to meet the requirements of IEC 1000-3-2 class A. The transient response due to load change is about one cycle and voltage drop is about 5V. According to measured results the proposed rectifier has the properties of high power factor, low current distortion and fast dynamic response, based on the proposed control algorithm.