MAGLEV TRAIN

We have always thought of aeroplanes as the fastest mode of transportation. As it travels thousands of miles in an hour we do not mind the flight delays and also the risk in flying. There is no other alternative to planes that can travel such a great distance in minimum amount of time. Buses, cars, boats and even conventional trains seem to be too slow in comparison to planes.

Now a new transportation mode has occurred that can clearly compete with planes in both speed and safety. They are called MAGLEV trains. The full form and the basic working principle of MAGLEV is called magnetic levitation.

Magnetic Levitation
The principle of magnetic levitation is that a vehicle can be suspended and propelled on a guidance track made with magnets. The vehicle on top of the track may be propelled with the help of a linear induction motor. Although the vehicle does not use steel wheels on a steel rail they are still referred to as trains as by definition they are a long chain of vehicles which travel in the same direction. This is the definition of a MAGLEV train.




As the frictional parts are minimum in this type of technology, the MAGLEV trains are known to have more speed, smoothness and less sound.

Working of MAGLEV Train
The train will be floating about 10mm above the magnetic guiding track. The train will be propelled to move by the guide way itself. Thus, there is no need of any engine inside he train. The detailed working of MAGLEV train is shown in the figure below. The train is propelled by the changing in magnetic fields. As soon as the train starts to move, the magnetic field changes sections by switching method and thus the train is again pulled forward. The whole guide way is run by electromagnets so as to provide the magnetic effect.



Thus the power needed for the whole process is less when compared to a conventional electric train. Amongst the power used, only a little is used for the levitation process. But a higher percentage of power is needed to overcome air friction.

MAGLEV v/s Conventional Train
The main difference between both the trains is that conventional trains need steel wheels and a steel track for their movement and MAGLEV does not need wheels. They travel under the principle of electromagnetic suspension.

Another difference is in the engine used. MAGLEV trains do not need engines like conventional trains. The engine used for conventional trains provide power to pull a chain of compartments along steel tracks. In MAGLEV trains, the power to propel the train is provided by the magnetic fields created by the electric coils kept in the guidance tracks which are added together to provide huge power.

MAGLEV Track
The track along which the train moves is called the guide way. Both the guide way as well as the train’s undercarriage also have magnets which repel each other. Thus the train is said to levitate about 0.39 inches on top of the guide way. After the levitation is complete, enough power has to be produced so as to move the train through the guide way. This power is given to the coils within the guide way, which in turn produces magnetic fields, which pulls and pushes the train through the guide way.








The current that is given to the electric coils of the guide way will be alternating in nature. Thus the polarity of the coils will be changing in period. Thus the change causes a pull force for the train in the front and to add to this force, the magnetic field behind the train adds more forward thrust.

Commercial use of MAGLEV Trains
The first known commercial use of MAGLEV train was in the year 1984 in Birmingham, England, and the train was named MAGLEV itself. But due to less reliability, the train was stopped by 1994.
The most famous commercial MAGLEV train is the Shanghai MAGLEV train in Shanghai, China. The train can go in a top speed of 270 miles/hour with an average speed of 160 miles/hour.
Since these trains move on a cushion of air, there is no friction at all [except air friction]. The trains are also aerodynamically designed which enables them to reach great speeds like 300 miles/hour and so on. At 300 miles/hour you can travel from Rome to Paris in about 2 hours.
EMS and EDS Systems
Some of the greatest developers of the MAGLEV trains are Germany and Japan. Although the basic concepts used for the construction are the same, the prototypes used are different. German trains use electromagnetic suspension (EMS) system so as the bottom of the train is wrapped to a steel guide way. Thus levitation occurs between the electromagnets that are attached underneath the train and the guide way to about 1 centimetre. It also helps in keeping the train in levitation, when it is standing still. Such trains were tested to go on a maximum speed of about 300 miles/hour with passengers on-board.

In Japan, MAGLEV trains use a technology called electro-dynamic suspension (EDS) system, which causes the trains to move due to the repelling force of magnets. The main difference with EMS is that, the electromagnets used will be super cooled and superconducting. Such magnets are prone to conduct current even if there is no power supply. Thus EDS system helps to save more power than EMS system. But the cooling mechanism and thus the initial cost will be expensive.

In EDS systems, the levitation distance is almost 10 centimetres above the guide way. This distance will need the use of rubber tires for the initial lift-off speed of the train [up to 62 miles/hour]. Since the EDS system produces superconducting magnetic field, people having pacemakers will have to be guarded from magnetic fields.

Advantages of MAGLEV
The main advantage is maintenance. There is no contact between the guide way and the train which lessens the number of moving parts. Thus the components that wear out is little.
Another advantage is the reduction in noise. As there are no wheels running along there is no wheel noise. However noise due to air disturbance will still be there.
The next advantage is high speed. As there are no frictional contacts, the train is prone to have more speed.
Another advantage is that the guide way can be made a lot thicker in uphill places, after stations and so on. This will help in increasing the speed of the train further.
Disadvantages of MAGLEV
The initial cost of MAGLEV trains are highly costly. The guide paths are also supposed to be more costly than conventional steel railways.

Environmental Friendliness of MAGLEV Trains
MAGLEV trains are more environmentally friendly than other types of trains.  In terms of energy consumption maglev trains are slightly better off than conventional trains. As there is no wheel friction with the ground, the resistive force gradually increases in the air friction. Thus the energy efficiency difference between a MAGLEV train and a conventional train is of very small margin.

Electrical and electronics latest seminars

EEE&ECE LATEST SEMINARS:


‘Cling-Film’ Solar Cells – A New Revolution for Renewable Energy

Scientists from the Universities of Sheffield and Cambridge have started a new research that promises to produce cost-effective and highly efficient cling film solar cells. The idea was first published in the journal “Advanced Energy Materials”. According to them, these solar cells can also be produced with much ease. This has clearly become a great advancement in the field of renewable solar energy.
To carry out the tests, the ISI Neutron Source and Diamond Light Source at STFC Rutherford Appleton Laboratory in Oxfordshire were used.
Until now, two types of solar cell materials are being used – plastic and silicon. When it comes to manufacturing of the material, plastic is known to be much much cheaper. Due to the simple manufacturing process, they can also be produced in huge quantities. When molecules having complex mixtures are spread on to a surface, the molecules move away from one another and start to accumulate at the top and bottom of the layer. Thus, a highly efficient solar cell is produced. This same principle was used by researchers to prove that by using much better and cost less manufacturing methods, where flexible layers of material are deposited over large areas like cling-film, highly efficient solar cell structures can be produced.
These solar cells are known to be useful for both home use as well as industrial use and since it is very cheap, it can be manufactured on a high-scale. Instead of using high-end fabrication methods to manufacture a certain semi-conductor nanostructure, high number of printing could be used to produce nano-scale films of solar cells that are much thinner than the width of a human hair. Such films can be used to produce cost-effective, light-weight solar cell panels.
According to Dr. Robert Dalgliesh, one of the researchers of the project, the work makes us understand the potential of the joint use of neutron and X-ray scattering sources such as ISIS and Diamond in solving modern challenges for society. Using such sources help in making a stronger internal structure for the solar cell. By studying the layers in the solar cell that is responsible in converting sunlight into electricity, the different processing steps that change the overall efficiency and affect the overall polymer solar cell performance is also known.
Since most of the energy consumed today is through non-renewable sources, the demand for something that generates energy through a renewable source like the Sun is needed for the coming years. Since no highly efficient system that is capable of converting sunlight into electricity has been found until now, the cling-film solar cell will clearly pave way for the new age of renewable energy
.

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Computer Clothing

There is a major movement going on in the electronics and computer industries to develop wearable devices for what’s being called Post-PC era. We are now at the dawn of that era and some of these devices are already making their way to the consumer market .Computerized clothes will be the next step in making computers and devices portable without having to strap electronics into our body. These digital clothes will able to perform some of the PC functions. These devices are small in size and portable. This apparel can be used to read our heart rate and breathing. The LED monitors could even be integrated into this apparel to display text and images.

CT scanning

CT scanning – computed tomography is a mechanism of getting the internal details of a section. It is a diagonostic imaging procedure in which anatomical information is digitally reconstructed from X-ray transmission data obtained by scanning an area from many directions in the same plane to visualize information in that plane. CT is a fast patient friendly and has the unique ability to image a combination of soft tissue, bone, lungs and blood vessels.

Data Compression Techniques

Data compression is the technique of converting an input data stream or the original data into another data stream which is shorter in length. There are many known methods for data compression. They are based on different ideas and are suitable for different types of data. But they all have the same principle that they compress data by removing the redundancy in the original data. Otherwise data compression can be looked up on as a change in representation from inefficient to efficient form.

Electromagnetic bombs

 Electromagnetic bombs are Weapons of Electrical Mass Destruction with applications across a broad spectrum of targets, spanning both the strategic and tactical. As such their use offers a very high payoff in attacking the fundamental information processing and communication facilities of a target system. The massed application of these weapons will produce substantial paralysis in any target system, thus providing a decisive advantage in the conduct of Electronic Combat, Offensive Counter Air and Strategic Air Attack. Generators would be useless, cars wouldn’t run, and there would be no chance of making a phone call. In a matter of seconds, a big enough e-bomb could thrust an entire city back 200 years or cripple a military unit. The basic principle used in an e-bomb is electromagnetic pulse effectEMP effect can result in irreversible damage to a wide range of electrical and electronic equipment, particularly computers and radio or radar etc. having military importance. Commercial computer equipment is particularly vulnerable to EMP effects.The technology base which may be applied to the design of electromagnetic bombs is both diverse, and in many areas quite mature. Key technologies which are extant in the area are explosively pumped Flux Compression Generators (FCG), explosive or propellant driven Magneto-Hydrodynamic (MHD) generators and a range of HPM devices, the foremost of which is the Virtual Cathode Oscillator or Vircator.

Electrical and chemical diagnostics of transformer insulation

This paper describes the application of two relatively new diagnostic techniques for the determination of insulation condition in aged transformers. The techniques are (a) measurements of interfacial polarization spectra by a DC method and (b) measurements of molecular weight and its distribution by gel permeation chromatography. Several other electrical properties of the cellulose polymer were also investigated. Samples were obtained from a retired power transformer and they were analysed by the developed techniques. Six distribution transformers were also tested with the interfacial polarization spectra measurement technique, and the molecular weight of paper/pressboard samples from these transformers were also measured by the gel permeation chromatography. The variation of the results through different locations in a power transformer is discussed in this paper. The possible correlation between different measured properties was investigated and discussed in this paper.

AUDIO SPOTLIGHTING

ABSTRACT

Audio spot lighting is a very recent technology that creates focused beams of sound similar to light beams coming out of a flashlight. By ‘shining’ sound to one location, specific listeners can be targeted with sound without others nearby hearing it. It uses a combination of non-linear acoustics and some fancy mathematics. But it is real and is fine to knock the socks of any conventional loud speaker. This acoustic device comprises a speaker that fires inaudible ultrasound pulses with very small wavelength which act in a manner very similar to that of a narrow column. The ultra sound beam acts as an airborne speaker and as the beam moves through the air gradual distortion takes place in a predictable way due to the property of non-linearity of air. This gives rise to audible components that can be accurately predicted and precisely controlled. Joseph Pompei’s Holosonic Research Labs invented the Audio Spotlight that is made of a sound processor, an amplifier and the transducer. The American Technology Corporation developed the Hyper Sonic Sound-based Directed Audio Sound System. Both use ultrasound based solutions to beam sound into a focused beam. Audio spotlight can be either directed at a particular listener or to a point where it is reflected.
The targeted or directed audio technology is going to a huge commercial market in entertainment and consumer electronics and technology developers are scrambling to tap in to the market. Being the most recent and dramatic change in the way we perceive sound since the invention of coil loud speaker, audio spot light technology can do many miracles in various fields like Private messaging system, Home theatre audio system, Navy and military applications, museum displays, ventriloquist systems etc. Thus audio spotlighting helps us to control where sound comes from and where it goes!

ASSYMETRIC DIGITAL SUBSCRIBER LINE (ADSL)

ABSTRACT
Digital Subscriber Lines (DSL) are used to deliver high-rate digital data over existing ordinary phone-lines. A new modulation technology called Discrete Multitone (DMT) allows the transmission of high speed data. DSL facilitates the simultaneous use of normal telephone services, ISDN, and high speed data transmission, e.g., video. DMT-based DSL can be seen as the transition from existing copper-lines to the future fiber-cables. This makes DSL economically interesting for the local telephone companies. They can offer customers high speed data services even before switching to fiber-optics.
DSL is a newly standardized transmission technology facilitating simultaneous use of normal telephone services, data transmission of 6 M bit/s in the downstream and Basic- rate Access (BRA). DSL can be seen as a FDM system in which the available bandwidth of a single copper-loop is divided into three parts. The base band occupied by POTS is split from the data channels by using a method which guarantees POTS services in the case of ADSL-system failure (e.g. passive filters).

EUVL

ABSTRACT

This paper discusses the basic concepts and current state of development of EUV lithography (EUVL), a relatively new form of lithography that uses extreme ultraviolet (EUV) radiation with a wavelength in the range of 10 to 14 nanometers (nm) to carry out projection imaging. Currently, and for the last several decades, optical projection lithography has been the lithographic technique used in the high-volume manufacture of integrated circuits. It is widely anticipated that improvements in this technology will allow it to remain the semiconductor industry’s workhorse through the 100 nm generation of devices. However, some time around the year 2005, so-called Next-Generation Lithographies will be required. EUVL is one such technology vying to become the successor to optical lithography. This paper provides an overview of the capabilities of EUVL, and explains how EUVL might be implemented. The challenges that must be overcome in order for EUVL to qualify for high-volume manufacture are also discussed.

Energy transmission system for an artificial heart- leakage inductance compensation

A power supply system using a transcutaneous transformer to power an artificial heart through intact skin has been designed. In order to realize both high-voltage gain and minimum circulating current, compensation of leakage inductances on both sides of a transcutaneous transformer is proposed. A frequency region which realizes the robustness against coupling coefficient and load variation is identified. In this region, the converter has inherent advantages such as zerovoltage switching (ZVS) or zero-current switching (ZCS) of the switches, high-voltage gain, minimum circulating current, and high efficiency. Artificial heart, energy transmission system, high efficiency, high-frequency converter, high-power density, high-voltage gain, inductance compensation, soft-switched converter, transcutaneous transformer, zero-current switching (ZCS), zero-voltage switching

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BiCMOS Technology

The need for high-performance, low-power, and low-cost systems for network transport and wireless communications is driving silicon technology toward higher speed, higher integration, and more functionality. Further more, this integration of RF and analog mixed-signal circuits into high-performance digital signal-processing (DSP) systems must be done with minimum cost overhead to be commercially viable. While some analog and RF designs have been attempted in mainstream digital-only complimentary metal-oxide semiconductor (CMOS) technologies, almost all designs that require stringent RF performance use bipolar or semiconductor technology. Silicon integrated circuit (IC) products that, at present, require modern bipolar or BiCMOS silicon technology in wired application space include the essential optical network (SONET) and synchronous digital hierarchy (SDH) operating at 10 Gb/s and higher. The viability of a mixed digital/analog. RF chip depends on the cost of making the silicon with the required elements; in practice, it must approximate the cost of the CMOS wafer, Cycle times for processing the wafer should not significantly exceed cycle times for a digital CMOS wafer. Yields of the SOC chip must be similar to those of a multi-chip implementation. Much of this article will examine process techniques that achieve the objectives of low cost, rapid cycle time, and solid yield

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Grid Network

ABSTRACT

Grid is as an emerging technology for enabling resource sharing and coordinated problem solving in dynamic multi-institutional virtual organizations. In the grid environment, resources may belong to different institutions, have different usage policies and pose different requirements on acceptable requests.
one of the fundamental operations needed to support location independent computing is resource discovery .It is the process of locating relevant resources based on application requirements of a user.
The description of a resource is essential for automated resource discovery and search, selection, matching, composition and interoperation, invocation and execution monitoring; different middle-ware specifies different rules for describing a resource. Hence, the information gathered from these diverse sources tends to be semantically heterogeneous and needs to be correlated.
Efficient resource discovery needs uniform unambiguous resource description. To date there is no universal resource description language common to all state of art grid middleware. Different grid middleware systems have different methods of resource description and it is not yet known how well these can interoperate. Hence, there is a need to utilize semantic matching of these resource descriptions.

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IEEE 802.11n –Next Generation Wireless Standard

ABSTRACT

The newest standard in Wireless LAN is called 802.11n. 802.11 is an industry standard for high-speed networking. 802.11n is designed to replace the 802.11a, 802.11b and 802.11g standards. 802.11n equipment is backward compatible with older 802.11gab and it supports much faster wireless connections over longer distances. So-called “Wireless N” or “Draft N” routers available today are based on a preliminary version of the 802.11n. The beta version of this standard is used now in laptops and routers. 802.11n will work by utilizing multiple input multiple output (MIMO) antennas and channel bounding in tandem to transmit and receive data. It contains at least 2 antennas for transmitting data’s. 802.11n will support bandwidth greater than 100 Mbps and in theory it can have a speed of 600 Mbps.It can be used in high speed internets, VOIP, Network Attach Storage (NAS), gaming. The full version will be implemented in the laptops and in the LANs in upcoming years

Adaptive Piezoelectric energy harvesting circuit

This paper describes an approach to harvesting electrical energy from a mechanically excited piezoelectric element. A vibrating piezoelectric device differs from a typical electrical power source in that it has a capacitive rather than inductive source impedance, and may be driven by mechanical vibrations of varying amplitude. An analytical expression for the optimal power flow from a rectified piezoelectric device is derived, and an “energy harvesting “ circuit is proposed which can achieve this optimal power flow. The harvesting circuit consists of an ac-dc rectifier with an output capacitor, an electrochemical battery, and a switch-mode dc-dc converter that controls the energy flow into the battery. An adaptive control technique for the dc-dc converter is used to continuously implement the optimal power transfer theory and maximize the power stored by the battery. Experimental result reveal that the use of the adaptive dc-dc converter increases power transfer by over 400% as compared to when the dc-dc converter is not used.

ANN Based Power System Restoration

Power System Restoration (PSR) has been a subject of study for many years. In recent years many techniques were proposed to solve the limitations of predetermined restoration guidelines and procedures used by a majority of system operators to restore a system following the occurrence of a wide area disturbance. This paper discusses limitations encountered in some currently used PSR techniques and a proposed improvement based on Artificial Neural Networks (ANNs). This proposed scheme has been tested on a 162-bus transmission system and compared with a breadth search transmission system. The results indicate that, this is a feasible option that should be considered for real time applications.
Artificial Neural Networks (ANNs) are computational techniques that try to obtain a performance similar to that of human’s performance when solving problems. The building block of ANN is Artificial Neuron, which has got structural & functional similarities with biological neurons. ANN is also an efficient alternative for problem solutions where it is possible to obtain data describing the problem behavior, but a mathematical description of the process is impossible. The proposed restoration scheme is composed of several Island Restoration Schemes (IRS). Each IRS is responsible for the development of an Island Restoration Plan when the power system is recovering from a wide area disturbance.

projects on robotics

Bluetooth based Robot for Metal Detection Applications

Title of the project: Bluetooth based Robot for Metal Detection

Applications

Domain: Robotics, Wireless Communication

Software: Embedded C, Keil, Proload

Microcontroller: AT89S52

Power Supply: +9V, 500mA Regulated Power Supply

Display: Television

Crystal: 11.0592MHz

Communication Device: RF Module

Transmitter: STT – 433MHz

Receiver: STR – 433MHz

Applications: Industries, Process Control, Domestic and Automotives

ABSTRACT

Path Finder was sent to Mars in 1998. This was a great achievement which detected the secrets of “Mars”. This project deals with RF controlled robot. This robot is prototype for the “Path Finder”.

This robot is controlled by a RF remote. This can be moved forward and reverse direction using geared motors of 60RPM. Also this robot can take sharp turnings towards left and right directions. This project uses AT89S52 MCU as its controller. A high sensitive induction type metal detector is designed using colpitts oscillator principle and fixed to this robot. Also a wireless camera with voice is interfaced to the kit.

When the robot is moving on a surface, the system produces a beep sound when metal is detected. This beep sound will be transmitted to remote place.

Simultaneously the images around the robot will be transmitted to remote place.

User can monitor the images and metal detection alarms on Television.

The RF modules used here are STT-433 MHz Transmitter, STR-433 MHz Receiver, HT640 RF Encoder and HT648 RF Decoder. The three switches are interfaced to the RF transmitter through RF Encoder. The encoder continuously reads the status of the switches, passes the data to the RF transmitter and the transmitter transmits the data.

This project uses 9V battery. This project is much useful for mines detection and surveillance applications

latest electrical seminars

Magneto-Optical Current Transformer

INTRODUCTION

                An accurate electric current transducer is a key component of any power system instrumentation. To measure currents power stations and substations conventionally employ inductive type current transformers with core and windings. For high voltage applications, porcelain insulators and oil-impregnated materials have to be used to produce insulation between the primary bus and the secondary windings. The insulation structure has to be designed carefully to avoid electric field stresses, which could eventually cause insulation breakdown. The electric current path of the primary bus has to be designed properly to minimize the mechanical forces on the primary conductors for through faults. The reliability of  conventional high-voltage current transformers have been questioned because of their violent destructive failures which caused fires and impact damage to adjacent apparatus in the switchyards, electric damage to relays, and power service disruptions.

                With short circuit capabilities of power systems getting larger, and the voltage levels going higher the conventional current transformers becomes  more and more bulky and costly also the saturation of the iron core under fault current and the low frequency response make it difficult to obtain accurate current signals under power system transient conditions. In addition to the concerns, with the computer control techniques and digital protection devices being introduced  into power systems, the conventional current transformers have caused further difficulties, as they are likely to introduce electro-magnetic interference through the ground loop into the digital systems. This has required the use of an auxiliary current transformer or optical isolator to avoid such problems.

                It appears that the newly emerged Magneto-optical current transformer technology provides a solution for many of the above mentioned problems. The MOCT measures the electric current by means of Faraday Effect, which was first observed by Michael Faraday 150 years ago. The Faraday Effect is the phenomenon that the orientation of polarized light rotates under the influence of the magnetic fields and the rotation angle is proportional to the strength of the magnetic field component in the direction of optical path.

                The MOCT measures the rotation angle caused by the magnetic field and converts it into a signal of few volts proportional to the electric currant. It consist of a sensor head located near the current carrying conductor, an electronic signal processing unit and fiber optical cables linking to these two parts. The sensor head consist of only optical component such as fiber optical cables, lenses, polarizers, glass prisms, mirrors etc. the signal is brought down by fiber optical cables to the signal processing unit and there is no need to use the metallic wires to transfer the signal. Therefore the insulation structure of an MOCT is simpler than that of a conventional current transformer, and there is no risk of fire or explosion by the MOCT. In addition to the insulation benefits, a MOCT is able to provide high immunity to electromagnetic interferences, wider frequency response, large dynamic range and low outputs which are compatible with the inputs of analog to digital converters. They are ideal for the interference between power systems and computer systems. And there is a growing interest in using MOCTs to measure the electric currents.

MOCT-PRINCIPLE

                The Magneto-Optical current transformer is based on the Faradays effect. Michael Faraday discovered that the orientation of linearly polarized light was rotated under the influence of the magnetic field when the light propagated in a piece of glass, and the rotation angle was proportional to the intensity of the magnetic field. The concept of Faraday Effect could be understood from the Fig.1.

 

Fig. 1

Generally, this phenomenon can be described as follows:

                                       q = Vdl    …………Eq(1)

‘q’ is the Faraday rotation angle,

‘V’ is the Verdet constant of magneto-optical material

‘B’ is the magnetic flux density along the optical path

‘l’ is the optical path

When the linearly polarized light encircles a current carrying conductor eq(1) can be rewritten as according to Ampere’s law as

 q =nmVI           ………….Eq(2)

‘I ‘is the current to be measured,

‘m’ is the permeability of the material,

‘n’ is the number of turns of the optical path.

                The Faraday effect outlined in eq(2) is a better format to apply to an MOCT, because the rotation angle in this case is directly related to the enclosed electric current. It rejects the magnetic field signals due to external currents which are normally quite strong in power system.

 

Fig. 2

                The typical application of the Faraday effect to an MOCT is clear from fig(2). A polarizer is used to convert the randomly polarized incident light into linearly polarized light. The orientation of the linearly polarized light rotates an angle q after the light has passed through the magneto-optical material because of Faraday Effect. Then another polarization prism is used as an analyzer, which is 45 ⁰  oriented with the polarizer, to convert the orientation variation of the polarized  light into intensity variation of the light with two outputs, and then these two outputs are send to photo detectors. The purpose of using the analyzer is that photo detectors can only detect the intensity of light, rather than the orientation of polarizations. The output optical signals from the analyzer can be described as,

P₁ = (1 + Sin 2q )

P₂ = (1 - Sin 2q )

P₀ is the optical power from the light source,

q is the Faraday rotation angle,

P₁ and P₂ are the optical power delivered by the detectors.

                In order to properly apply Eq(2) in the MOCT design by making the optical path wrap around the current carrying conductor, the optical path has to be folded by reflections. Total internal reflections and metal reflections are good ways to achieve this. However reflections introduce phase shift; hence change the polarization state of the light. The optical prism has to be designed to keep the light going through the MOCT linearly polarized. In order to stimulate the behavior of the polarized light reflect through the glass prism of an MOCT, ie to maintain the light traveling through the glass prism to be linearly polarized and also for the analysis of the effects of dielectric and metal reflections on the linearly polarized light, a computer programme is written in FORTARN  language. Stimulation results include information such as polarization state change at each reflection and the overall responsibility of the optical sensor.

DESIGN

 

Fig. 3

                Fig (3) shows the structure of this MOCT. The optical sensor consists of two separate clamp-on parts. In each part of the device, linearly polarized light is arranged to pass through the optical glass prism to pickup the Faraday rotation signal. The polarization compensation technique is applied at each corner of the prisms, so that the light passing through the prism remains linearly polarized. At the other end of the prism, a silver mirror reflects the light beam so that light beam comes back to its sending end via the same route while accumulating the Faraday rotations.

 

Fig. 4

            The two halves can be assembled around the conductor. Thereby, the rotation angles from the two halves of the sensor [Fig.4(a)] are added up in the signal processing unit so that the total rotation angle (q1+q2 ) is the same as the rotation angle q from the optical path shown in Fig4(b), which is two turns around the conductor

 

Fig. 5

                Fig. 5 shows the structure of the housing for the clamp-on MOCT. The optical glass prism polarizes, and lenses are completely sealed in the housing by epoxy, so that they are free of environmental hazards such as dust and moisture. This structure avoids the use of magnetic material to concentrate the magnetic field as found in some other MOCT design and Hall Effect current measurement devices. There for it is free from the effect of remanent flux, which could affect the accuracy of the current measurement.

MAGNETO-OPTICAL SENSOR

                Almost all transparent material exhibits the magneto-optical effect or Faraday Effect, but the effect of some of the material is very temperature dependent, and they are not suitable for the sensing material. The optical glasses are good candidate for the sensing material, because the Verdet constants are not sensitive to the temperature changes, and they have good transparency properties. They are cheep and it is easy to get large pieces of them. Among the optical glasses SF-57  is the best choice, as it has larger Verdet constant than most of the other optical glasses. And MOCT made out of these materials can achieve higher sensitivity. In the MOCT, from Eq (2), the total internal rotation angle is,

q                        » q₁+ q₂ » 2mVI         

Where I is the current to be measured,

                     m = 4p x 10^-7 H/m

     V=7.7 x 10² degrees/Tm at a wavelength of  820nm

Therefore q = 1.9 degrees/ KA.

                Different optical fibers are designed for different usage. The single mode fiber has very wide bandwidth, which is essential for communication systems, but it is difficult to launch optical power into the single mode fiber because of it’s very thin size. While large multimode fiber is convenient for collecting maximum amount of light from the light source, it suffers from the problem of dispersion which limits its bandwidth. In the situation of power system instrumentation, only moderate frequency response is required and in MOCT, the more optical power received by the detectors the better signal to noise ratio can be achieved. Therefore, the large core multi-mode optical fiber is used here to transfer the optical signals to and from the optical sensors.

ELECRONIC CIRCUIT FOR THE MOCT

 

Fig. 6

                Fig. 6 shows the schematic diagram of the electronic circuit for the clamp-on MOCT. In order to make use of the dynamic range of the digital system as well as the different frequency response requirements of metering and relaying, metering signal (small signal) and relaying signal (large signal) are treated differently. Two output stages have been designed accordingly. One stage, which has 1 KA dynamic range, is for power system current metering, and other stage, which operate up to 20 KA, provides power system current signals for digital relay systems.

                In each part of the device, the sum of the two receiving channels signals, which have the same DC bias aI₀, differenced at junction with a reference voltage V_ref from the power level adjustment potentiometer. Then an integrator is used to adjust the LED driver current to maintain 2aI₀ to be the same as the V_ref at the junction. Because the reference voltage V_ref is the same for both the sides, the DC bias aI₀ and the sensitivities  2aI₀ of the two halves of the clamp-on MOCT are considered to be stable and identical.

                The difference of the two receiving channels signals 2aI₀ (2Sinq₁) and 2aI₀ (2Sinq₂) in each part of the device are added directly and then fed through an amplifier for the small signals. At the same time these two signals are processed digitally to do a sin^-1 calculation on each and then summed together for the large signal situation when the non-linearity of the MOCT can no longer be ignored. The ratio responses of the two output stages of the clamp-on MOCT are designed as 10V/KA and 0.5V/KA and frequency responses are 4KH_Z and 40 KH_Z respectively.

APPLICATION

                The MOCT is designed to operate in a transparent manner with modern electronic meters and digital relays, which have been adopted for a low energy analog signal interface. Typically, the design approach is to redefine the interface point as to input the analog to digital conversion function used by each of these measurement systems.

ADVANTAGES OF MOCT

1.      No risk of fires and explosions.

2.      No need to use metallic wires to transfer the signal and so simpler insulation structure than conventional current transformer.

3.      High immunity to electromagnetic interference.

4.      Wide frequency response and larger dynamic range.

5.      Low voltage outputs which are compatible with the inputs of digital to analog converters.

DISADVANTAGES OF MOCT

1.      Temperature and stress induced linear birefringence in the sensing material causes error and instability.

2.      The accuracy of MOCT is so far insufficient for the use in power systems.

CONCLUSION

                This paper presents a new kind of current transducer known as magneto optical current transducer. This magneto optical current transducer eliminates many of the drawbacks of the conventional current transformers. In an conventional current transformers, there is a chance of saturation of magnetic field under high current, complicated insulation and cooling structure, a chance of electro magnetic interference etc.

                By applying Faraday’s principle this transducer provides an easier and more accurate way of current measurement. This MOCT is widely used in power systems and substations nowadays. And a new trend is being introduced, which known as OCP based on adaptive theory, which make use of accuracy in the steady state of the conventional current transformer and the MOCT with no saturation under fault current transients.