Mhd Report

  • Upload
    priya91

  • View
    267

  • Download
    25

Embed Size (px)

Citation preview

A

SEMINAROn

MAGNETOHYDRODYNAMIC GENERATOR

\ vivek upadhyay

EE-32 (08054200108)

Affiliated to Uttar Pradesh Technical University, Lucknow

Electrical Engineering

Department Of

CERTIFICATEThis is certified that the seminar entitled MAGNETOHYDRODYNAMIC GENERATOR being submitted by CHANDRA KUMAR CHAUDHARI in partial fulfillment of the requirement for the award of degree of BACHELOR OF TECHNOLOGY in ELECTRICAL ENGINEERING, Uttar Pradesh Technical University, Lucknow under our supervision and guidance during the academic session 2007-08.

GuideMr. SURESH CHANDRA ASTHANA Mr. RISHI

FACULTY Electrical Engineering Department

H.O.D. ElectricalEngineeringDepartment

ACKNOWLEDGEMENT

I am highly obliged to the faculty members of Electrical Engineering Department of Babu Banarasi Das National Institute of Technology & Management, Lucknow for providing sincere guidance in preparing this report. I would also like to put forward my heartfelt thank to the faculty members of our department, specially Mr. Rishi Asthana, HOD, Electrical Engineering. I would also like to take this opportunity to thank Mr. Suresh Chand who provided their sincere advice at every step.

V ivek upadhyay EE-32 U PTU ROLLNO- 08054200108

CONTENTS

Introduction to MHD Introduction to MHD Generator. Principle of MHD Generator. MHD Generator Design Working of MHD Generator. Existing MHD generator of various types. Problem related to different type generator. Electrode used in MHD generator. Pamir 3-U MHD power system.

Result of acceptance test program on 3-U MHD power system. Advantages & Disadvantanges of MHD Generator. References

MAGNETOHYDRODYNAMICS (MHD)It is the academic discipline which studies the dynamics of electrically conducting fluids. The idea of MHD is that magnetic fields can induce currents in a moving conductive fluid, which create forces on the fluid, and also change the magnetic field itself. The set of equations which describe MHD are a combination of the Navier-Stokes equations of fluid dynamics and Maxwell's equations of electromagnetism. These differential equations have to be solved simultaneously, either analytically or numerically. Because MHD is a fluid theory, it cannot treat kinetic phenomena, i.e., those in which the existence of discrete particles, or of a non-thermal distribution of their velocities, is important.

INTRODUCTION TO MAGNETOHYDRODYNAMICS GENERATORS

The MHD (magnetohydrodynamic) generator or dynamo transforms thermal energy or kinetic energy directly into electricity. MHD generators are different from traditional electric generators in that they can operate at high temperatures without moving parts. MHD was eagerly developed because the exhaust of a plasma MHD generator is a flame, still able to heat the boilers of a steam power plant. So high-temperature MHD was developed as a topping cycle to increase the efficiency of electric generation, especially when burning coal or natural gas. It has also been applied to pump liquid metals and for quiet submarine engines. The basic concept underlying the mechanical and fluid dynamos is the same. The fluid dynamo, however, uses the motion of fluid or plasma to generate the currents which generate the electrical energy. The mechanical dynamo, in contrast, uses the motion of mechanical devices to accomplish this. The functional difference between an MHD generator and an MHD dynamo is the path the charged particles follow. MHD generators are now practical for fossil fuels, but have been overtaken by other, less expensive technologies, such as combined cycles in which a gas turbine's or molten carbonate fuel cell's exhaust heats steam for steam turbine. The unique value of MHD is that it permits an older single-cycle fossil-fuel power plant to be upgraded to high efficiency.

Natural MHD dynamos are an active area of research in plasma physics and are of great interest to the geophysics and astrophysics communities. From their perspective the earth is a global MHD dynamo and with the aid of the particles on the solar wind produces the aurora borealis. The differently charged electromagnetic layers produced by the dynamo effect on the earth's geomagnetic field enable the appearance of the aurora borealis. As power is extracted from the plasma of the solar wind, the particles slow and are drawn down along the field lines in a brilliant display over the poles. This type of thruster generates magnetic fields by passing an electric current through a liquid conductor, such as sea water. Using another magnetic field, the liquid can be pushed in a chosen direction, therefore generating thrust. You can easily make one of these devices from household materials and a couple of neodymium magnets. In the diagram below the small arrows represent the intersecting electric and magnetic fields. the large blue arrow represents the flow of water.

ILLUSTRATION OF FORCES IN MHD SYSTEM

PRINCIPLE OF MHD GENERATOR

The Lorentz Force Law describes the effects of a charged particle moving in a constant magnetic field. The simplest form of this law is given by the vector equation.

F is the force acting on the particle (vector), Q is charge of particle (scalar), v is velocity of particle (vector), x is the cross product, B is magnetic field (vector).

The vector F is perpendicular to both v and B according to the Right hand rule

A VIEW OF MHD GENERATOR

MHD GENERATOR DESIGNFaraday generatorThe Faraday generator is named after the man who first looked for the effect in the Thames river (see History, below). A simple Faraday generator would consist of a wedgeshaped pipe or tube of some non-conductive material. When an electrically conductive fluid flows through the tube, in the presence of a significant perpendicular magnetic field, a charge is induced in the field, which can be drawn off as electrical power by placing the electrodes on the sides at 90 degree angles to the magnetic field. There are limitations on the density and type of field used. The amount of power that can be extracted is proportional to the cross sectional area of the tube and the speed of the conductive flow. The conductive substance is also cooled and slowed by this process. MHD generators typically reduce the temperature of the conductive substance from plasma temperatures to just over 1000 C. The main practical problem of a Faraday generator is that differential voltages and currents in the fluid short through the electrodes on the sides of the duct. The most powerful waste is from the Hall effect current. This makes the Faraday duct very inefficient. Most further refinements of MHD generators have tried to solve this problem. The optimal magnetic field on duct-shaped MHD generators is a sort of saddle shape. To get this field, a large generator requires an extremely powerful magnet. Many research groups have tried to adapt superconducting magnets to this purpose, with varying success.

Hall generatorThe most common answer is to use the Hall effect to create a current that flows with the fluid. The normal scheme is to place arrays of short, vertical electrodes on the sides of the duct. The first and last electrodes in the duct power the load. Each other electrode is shorted to an electrode on the opposite side of the duct. These shorts of the Faraday current induce a powerful magnetic field within the fluid, but in a chord of a circle at right angles to the Faraday current. This secondary, induced field makes current flow in a rainbow shape between the first and last electrodes. Losses are less than a Faraday generator, and voltages are higher because there is less shorting of the final induced current. However, this design has problems because the speed of the material flow requires the middle electrodes to be offset to "catch" the Faraday currents. As the load varies, the fluid flow speed varies, misaligning the Faraday current with its intended electrodes, and making the generator's efficiency very sensitive to its load.

Disc generatorThe third, currently most efficient answer is the Hall effect disc generator. This design currently holds the efficiency and energy density records for MHD generation. A disc

generator has fluid flowing between the center of a disc, and a duct wrapped around the edge. The magnetic excitation field is made by a pair of circular Helmholtz coils above and below the disk. The Faraday currents flow in a perfect dead short around the periphery of the disk. The Hall effect currents flow between ring electrodes near the center and ring electrodes near the periphery. Another significant advantage of this design is that the magnet is more efficient. First, it has simple parallel field lines. Second, because the fluid is processed in a disk, the magnet can be closer to the fluid, and magnetic field strengths increase as the 7th power of distance. Finally, the generator is compact for its power, so the magnet is also smaller. The resulting magnet uses a much smaller percentage of the generated power

WORKING OF MAGNETOHYDRODYNAMIC GENERATORIt is basically relates to the conversion of thermal energy to electrical energy using the magneto hydrodynamic principle which eliminates the turbine or engine used in conventional conversion systems. In MHD generators a conducting fluid is caused to flow through a channel placed between the poles of an electro magnet. An electric current is induced in the fluid at right angles to both the direction of fluid flow and the magnetic flux and is utilized by an external load connected across electrodes placed in contact with the fluid. A magneto-hydrodynamic (MHD) electric generator, works on the principle that any conductor of electricity that is moved through a magnetic field will generate in itself a current of electricity. This applies not only to copper wires (as in conventional generators), but to gases, which become conductors when they are made so hot that some of their atoms separate (ionize) into electrically charged particles. If forced through a magnetic field, a stream of ionized gas causes an electrical current to flow across it. The gas must be so hot (at least 4,000 F.) that it destroys many structural materials. Another problem is the poor conductivity of most gases big enough to supply commercial power. A major advantage: an MHD generator has no primary moving parts, with the exception of those in the relatively simple compressor. Coal is burn in a stream of compressed, preheated air. While passing through the flame, the air gets hotter, expands . A small amount of potassium chloride fed into it increases its ionization and makes it a better electrical conductor. Then the stream shoots into a hollow cone made of a heatresisting, nonconducting material . Electrical coils outside the cone create a strong magnetic field. As the gas speeds through, a powerful current of electricity flows across it and is collected by two electrodes inside the cone. From Nose Cones:-. Most of the electricity generated by the system comes from the electrodes, but waste heat can be harnessed to drive a conventional turbogenerator, adding importantly to the system's efficiency Most of the electricity generated by the system comes from the electrodes, but waste heat can be harnessed to drive a conventional turbogenerator, adding importantly to the system's efficiency. The estimation is that a 450,000-kw. coal-fired MHD generator will produce electricity with the sensational thermal efficiency of 55%. The best that conventional plants can do is 40%.

Even more exciting is the possibility of using the MHD system with a nuclear reactor. In this case the gas will probably be argon or helium, laced with cesium to make it more conductive. It will circulate through the reactor, then through the generator and back to the reactor again. This system will have to wait for the development of high-temperature reactor cores, but Project Rover, the Atomic Energy Commission's nuclear-rocket program, has shown that the prospects of this are promising.

DIAGRAM SHOWING ARRANGEMENT OF FORCES IN DIFFERENT

MODES OF GENERATOR DESIGN

Existing MHD generators are of various types1. Plasma:A fuel/air mixture seeded with an ionizing element is burned to produce a high temperature conducting gas mixture (plasma) which is expanded through the MHD channel. Plasmas1 are relatively poor conductors, even at the high operating temperatures employed (typically about 3000C) and superconducting (magnets with flux densities up to 6T are required to boost output. Because of the high operating temperature and flux density, plasma generators can only be considered for large scale systems.

2. Liquid Metal:In this type the conducting fluid is a liquid metal used in conjunction with a seperate thermodynamic working fluid to move it through the MHD channel. As high temperatures are not required to impart conductivity to the fluid as is the case with plasma generators lower temperature heat sources and lower strength magnets can be utilized making these generators more suitable for small scale installations. The two main types of such generators use a single phase or a two phase medium in the MHD channel.

Two Phase:The thermodynamic fluid is injected into hot liquid metal in a mixer ahead of the MHD channel. Combinations used or proposed are organic fluids and sodium-potassium eutectic mixtures for low temperature systems, water and tin for medium temperature systems, and helium and sodium or lithium for high temperature systems. The working fluid expands and the resultant two phase mixture of gas and liquid metal accelerates through the MHD channel producing electric power. From the MHD channel the mixture enters a nozzle where further acceleration occurs followed by separation of the components in a rotating separator. The metal passes through a diffuser which converts part of its kinetic energy to potential energy in the form of pressure sufficient to force it through the primary heat exchanger where it is reheated before returning to the mixer to continue the process. From the separator the vapour or gas still at high temperature passes through a regenerator where a proportion of its sensible heat- is transferred to the working fluid on route to the mixer. The partially cooled vapour or gas from the regenerator is then further cooled in a reject heat exchanger, vapour condensing to liquid which is pumped back to the mixer via the regenerator. In the case of a gaseous working fluid the cool gas from the reject heat exchanger is compressed and returned to the mixer via the regenerator

In MHD generators a conducting fluid is caused to flow through a channel placed between the poles of an electro magnet. An electric current is induced in the fluid at right angles to both the direction of fluid flow and the magnetic flux and is utilized by an external load connected across electrodes placed in contact with the fluid.

Producing alternating current through MHD generator:Producing an alternating current by maintaining a constant magnetic field and causing the liquid metal to periodically change its direction of flow through the MHD channel. This is effected by means of two closed vertical cylinders connected at the bottom by a horizontal pipe incorporating a MHD cell. The cylinders are partially filled with liquid potassium which acts as the conducting fluid. The primary heat source is nuclear and a primary heat exchanger is provided to vapourize potassium which is the thermodynamic working fluid. A reject heat exchanger is provided to condense the vapour. In operation high pressure potassium vapour from the primary heat exchanger is piped to the cylinders where it is admitted to one of them above the liquid potassium level through an inlet valve. At the same time an exhaust valve in the second cylinder is opened. This causes the liquid potassium to be forced from the first cylinder through the MHD channel to the second cylinder generating a current in one direction. The vapour exhausted from the second cylinder is piped to the reject heat exchanger where it is condensed to liquid and pumped back to the primary heat exchanger for reheating. Movement of the liquid metal is stopped by the head of the second cylinder where upon the inlet valve on the first cylinder is shut and the exhaust valve on the second cylinder is also shut. At the same time an inlet valve on the second cylinder is opened and an exhaust valve on the first cylinder is also opened, causing the liquid potassium to be forced back through the MHD channel in the reverse direction. This cycle is repeated continuously resulting in the generation of an alternating current

Main problems with these forms of generators are that:-

(a) The electrical output is in the form of direct current which is not easily converted to alternating current for general use because of the very low voltage and wide voltage and current swings. (b) The MHD cell internal resistance losses are high due to the presence of non-conductive vapour or gas bubbles in the liquid metal and the high temperature of the liquid metal. (c) The nozzle, separator and diffuser are sources of high losses.

Single Phase:It consists of a vertical U tube the limbs of which terminate in a tank, the tube and tank are filled with liquid metal. The liquid metal is heated at the bend of the U tube and a thermodynamic working fluid is injected into the metal at the base of one of the limbs. The working fluid vapourizes forming a two phase mixture which is less dense than the contents of the other limb and is thus forced upwards. The vapour and liquid metal separate in the tank whereby the vapour is then condensed and returned as liquid to the base of the first limb and the liquid metal runs into the second limb to maintain circulation. A MHD channel forms part of the second limb and converts the potential energy of the liquid metal in the tank to electrical energy. Because the fluid flowing in the MHD channel is single phase (i.e. liquid metal only), some of the problems of the two phase form such as large current and voltage swings are avoided. Also, the absence of vapour bubbles reduces the MHD cell internal resistance losses and the higher conductivity of the fluid in the cell allows the use of less powerful magnets. Furthermore, the high loss nozzle, separator and diffuser are eliminated.

Other Problems:(a) The electrical output is in the form of a very low voltage direct current. (b) MHD cell internal resistance losses increase as the temperature of the liquid metal increases. (c) Bubble slip relative to the liquid metal reduces efficiency. (d) A large mass of expensive liquid metal is needed. (e) The plant is very bulky. One of the main draw backs of the above systems is that they all produce low voltage direct current which must be converted to high voltage alternating current for trans mission and general use and this introduces further com plexities and losses.

ELECTRODE USED IN MHD GENERATOR:1. An MHD power generator comprising means for generating a weakly ionized plasma stream, a pair of electrodes made of magnetic material and arranged opposite to each other, means for defining a plasma passage between the pair of electrodes through which the plasma stream flows from the plasma stream generating means, means for cooling the pair of electrodes, and a plurality of output lines each connected to the mutually facing electrodes so as to take out an electric power generated there between. 2. An MHD power generator according to claim 1, in which said pair of electrodes are made of ferromagnetic materials. 3. An MHD power generator according to claim 1, in which said pair of electrodes each comprises a plurality of segmented electrodes with an insulating material disposed between the next adjacent segmented electrodes. 4. An MHD power generator according to claim 1, in which said pair of electrodes are made of ferromagnetic materials and said cooling means is adapted to permit the temperature of those surfaces of the electrodes which are in contact with the plasma stream to be maintained at 1200-1800 K. 5. An MHD power generator according to claim 1, in which said pair of electrodes each comprises a plurality of segmented electrodes with an insulating material disposed between the next adjacent segmented electrodes, the segmented electrodes each having a recess at that surface in contact with the plasma stream. 6. An MHD power generator according to claim 2, in which said ferromagnetic material has a maximum specific magnetic permeability of more than 1000. 7. An MHD power generator according to claim 1, in which that surface of the electrodes which is in contact with the plasma stream is coated with a coating material. 8. An MHD power generator according to claim 7, in which said coating material is a ceramic. 9. An MHD power generator comprising means for generating a weakly ionized plasma stream, a pair of electrodes arranged opposite to each other and comprising a block made of magnetic material and frame means made of an electrically and thermally conductive material and adapted to cover the block, a cooling medium passage provided in said frame means, means for defining a plasma passage between the pair of electrodes through which the plasma stream flows from the plasma stream generating means, means for supplying a cooling medium into the cooling medium passage to cool the electrodes, and a plurality of output lines each connected to the mutually facing electrodes so as to take out an electric power generated there between. 10. An MHD power generator according to claim 9, in which said pair of electrodes are made of ferromagnetic material.

11. An MHD power generator according to claim 9, in which said pair of electrodes are each constituted by a plurality of segmented electrodes connected so that an insulator is disposed between the adjacent segmented electrodes. 12. An MHD power generator according to claim 9, in which said pair of electrodes are made of ferromagnetic material and said cooling medium supply means serves to permit the temperature of those contact surfaces of the electrodes which are in contact with the plasma stream to be maintained within a range of 1200 to 1800 K. 13. An MHD power generator according to claim 9, in which said ferromagnetic material has a maximum specific magnetic permeability .mu. max of more than 1000. 14. An MHD power generator according to claim 9, in which those surfaces of the electrodes which are in contact with the plasma stream are coated with coating material. 15. An MHD power generator according to claim 15, in which said coating material is a ceramic

PAMIR - 3U MHD POWER SYSTEM:-

Pamir-3U MHD power system, shown, is a self-excited pulsed MHD generatordriven by three solid propellant plasma generators. The power system consists of three MHD channels designed and built by Nizhny Novgorod, which are placed between the electromagnet coils delivered by Nizhny Novgorod; three plasma generators designed and built by Soyuz; switching and protection equipment and a magnetballast resistor designed and built by Nizhny Novgorod; and the initial excitation subsystem (IES) and the control, measuring, monitoring, and recording subsystem (CMMRS), designed and built by IVTAN.' Textron was the system integrator and importer of the Pamir-3U equipment and overall project manager. The design requirements for the Pamir-3U MHD generator were established at the beginning of the program. The main system design parameters are listed in Table 1. The system design was based on the previously demonstrated, truck transportable, twochannel IVTAN Pamir-2 MHD power system hardware.' Because the specifications of the sponsoring agency required a higher power level, a third MHD channel was necessary.

The Pamir-3U MHD power system is designed for the conversion of the kinetic and thermal energies of the ionized pro-pellant combustion products flowing through the magnetic field to electrical energy. The main power unit components are shown in Fig. 2. These components are (1) plasma generators with MHD channels and stops; (2) a magnet system; (3) frame, (4), (5) shields; (6) stops; (7) supports; (8) buses; (9) strapping tapes; (10) base plate; and (11) plate. The shields (4) and (5) and the plate (11) are used for protection of the power unit components and the test site from the heating action of the high-temperature flow of combustion products. The material of the shields is a mineral glass-reinforced plastic of 12-mm thickness. The mass of the power unit with the plasma gen erators is 12,700 kg. The overall dimensions of the unit are a length of 4500 mm, a width of 2000 mm, and a height of 2080 mm

The magnet system is installed on. a frame that is attached to the base plate. The MHD channels are placed between four electrical magnets of the magnet system. The longitudinal axes of the MHD channels are inclined at an angle of 19 deg to the horizontal. The power-producing sections of the MHD chan nels are contained within the magnet system. The plasma generators rest on supports and are attached to them by a yoke with a metal band. The reactive force arising from the operation of the plasma generators is contained by the stops attached to the base plate. For electrical isolation and prevention of current leakage from the electrical circuit, which contains the electrodes of the MHD channel, the front and back ends of the plasma generators, and the propellant combustion products, there are mineral fiber glass-reinforced plastic insulated plates and isolation blocks made from the same material.

The electrical assembly is made of flat copper buses, (8), which are shown in Fig. 2. The bus cross sections are 100 mm X 10 mm and 80 mm X 100 mm. The buses with a direct operating voltage of 2.5 kV are insulated from the power unit components, which are grounded. For the purpose of decreasing the contact resistance, a tin coating with a nickel precoat is applied to the bus contact surfaces. The bus connections are made with standard fasteners. The plasma generators use a cesium-seeded solid rocket propellant. The BP-10F plasma charge propellant is a doublebased compound (nitrocellulose and nitroglycerin) with a 95/5 aluminum/magnesium alloy (-20% by mass) and cesium nitrate (-10% by mass) added to the propellant mixture. The SPK-10M and SPK-14S plasma charge compositions are similar, but use potassium nitrate instead of cesium nitrate. The actual percentages varied slightly from batch to batch. The thermal power released during Pamir-3U operations is approximately 600 MW. Under these operating conditions, the combustor stagnation temperature was estimated to be -3900 K, and the MHD channel inlet electrical conductivity was estimated to be in the range of 50 - 60 mho/m. More complete details of the burning rate characteristics of each batch are provided in Ref. 1. The plasma generators were similar in design and performance to those used for the Pamir 2 system.

2. Pamir-3U system power unit.The variations of the plasma generator parameters - mass flow rate (18.5 - 26.0 kg/s), operating time (7.4 - 10.5 s), and combustion pressure (34 - 52 atm) - are caused by variations of the burning rate of the propellant, as well as by the dependence of the burning rate on the initial charge temperature, which is normally 5 - 35'C. For operation of the MHD power system in the maximum pulse-duration mode, a special modification of the plasma generator with the initial charge temperature of O'C and an enlarged throat area of 80 cm' was analyzed and approved for use during the acceptance test program. Similarly, a separate analysis was approved for plasma generator charge operation at 40'C for the acceptance tests. This analysis, which results in the approval of only the plasma charge batch being assessed, is based on archival data of pre-vious batches, mechanical and

chemical data of the batch of interest, and actual performance data of the batch during operation. If the appropriate criteria are satisfied, operation at initial charge temperatures outside of the 5 - 350 C range is possible. The Pamir-3U MHD generator is a Faraday-type generator with continuous electrodes. The generator operates at a relatively high pressure to keep the Hall parameter relatively low. The MHD channel consists of three areas: inlet, power-producing zone, and outlet. In the inlet area, the combustion products are accelerated up to a Mach number of 2.4. In the power- producing zone, the MHD energy conversion occurs. The outlet area is intended for the exhaust of the combustion products and the protection of the magnet system from the heat load of the gas flow. The MHD channel is a heat-sink unit. The heat protection is achieved through heat absorption by the design components that are made from heatabsorbing materials: ceramics and mineral fiberglass-reinforced plastic. The channel exit temperature was estimated to be -3000 K.

(3)Pamir-3U magnet system.The power-producing zone of the MHD channel consists of two electrode walls with constant divergence and two parallel insulating walls. The inlet area is 159 mm X 159 mm, and the exit area is 159 mm X 258 mm. The length of the MHD power-producing zone is 1008 mm. The Pamir-3U magnet system principal views are shown in Fig. 3. The magnet system consists of four round electromagnets: (1) one left electromagnet; (2), (3) two middle electromagnets; (4) and one right electromagnet; (5), (6) which are separated by glassreinforced plastic inserts; and (7) tightened by three studs; (8) commutating buses; and (9) protected from the exhaust gases by shields. The right and the left electromagnets each consist of a single electromagnet and cover, and the middle electromagnets, which differ from each other by the commutation of the current buses, consist of two single electromagnets.

For the convenience of the MHD channel installations, the upper inserts (6), shown in (3) are removable, and the lower inserts are fixed to the middle electromagnets (2 and 3), and the right electromagnet (4). Commutating buses (8) are mounted in the lower part of the magnet system and brought out through the insert windows of the single electromagnet. The magnet coils are made of copper and are wound in an ellipsoid shape. There are 64 turns per coil. Each coil is insulated through the application of case insulation and its impregnation with an epoxy compound, followed by pressure and temperature polymerization of the insulation. The magnetic field in the magnet central region is 0.247 and 0.204 T/kA for the two side magnets. The magnet temperature at the end of a test run is less than 100'C, and the magnet cooldown time for the next test is less than 24 h. The IES, which is based on the use of a battery bank, is used to provide the electrical energy necessary for the initial magnetic field over the MHD channel working volume. The system includes a current source, charger, switching, protection and interlock devices, and transducers and measuring instrumentation. The CMMRS includes the computer for control and recording of the test parameters, the ignition unit used for plasma generator initiation, the control board, the primary electric power supply system, and the connecting cables and fiber-optic lines. The number of channels for measurement and recording is 16, which includes six electrical current measurements, four voltage measurements. four pressure measurements, and two spare channels.

SYSTEM OPERATION:The MHD generators are connected in a series/parallel arrangement. During the initial stage of self-excitation, all three of the MHD generator channels supply power to the electromagnet. During nominal steady-state operating conditions, all three MHD channels operate in the circuit with the electromagnet, but two of them, connected in parallel circuits, also supply power to the load. Figure 4 shows a circuit diagram of the power unit, load circuit, initial excitation system, and the magnet circuit. The detailed description of the Pamir-3U pulsed portable MHD power system and its parameters has been presented in Ref.1.

Pamir-3U MHD power system electrical circuit. The MHD power systen operates in the following manner. For the initial state of the MHD power system, all components and subsystems are in the ready mode and available for service. At the very beginning of the operating process, the thyristor switches, VS, are closed (switch Q is closed) by a command from the CMMRS that initiates a discharge from the IES for 1.5 - 1.6 s. Based on the analysis of the operation of the IES, approximately 0.5 s before the magnet current is expected to achieve 3 kA, the CMMRS generates a command to start the plasma generators. This process initiates the MHD channel electrode warm-up, which results in a decrease of the electrode voltage drop. When the magnet current reaches 3 kA, the CMMRS generates a command to the contactor, CM1, and connects the MHD generators to the magnet system, and the MHD power system selfexcitation process begins. When thevoltage of the MHD generators exceeds the voltage of thestorage battery, the thyristor switches, VS, disconnect the IES from the magnet system automatically. Then, the switch Q is opened by a command from the CMMRS, and the IES cunent is switched off. For current limitation and in case of excess magnet current over the maximum allowable value, the disconnectors DCI and DC2 switch a ballast resistor into

the circuit by a command from the CMMRS. During the self-excitation process, when the magnet current increases up to the specified value, but not more than 16 kA, the CMMRS generates a command to connector CM2 that switches the load into the circuit. After the operation ends, the energy stored in the magnet system is dissipated in the resistances of the magnet system and of the protection unit, PU.

RESULT OBTAINED DURING ACCEPTANCE TEST PROGRAMA preliminary acceptance test program, consisting of five power tests and several preliminary tests, was conducted during August 1994 at Geodesiya Research and Development Institute, Krasnoarmejsk, Russia. During this test program, net power levels as high as 15 MW. were obtained. Operation of the system in various operating modes was demonstrated, and several tests were conducted where the resistance was variedduring the hot-fire test run. The final Pamir-3U MHD power system acceptance test program was conducted at Aerojet Corporation, Sacramento, California, and consisted of eight hot fire tests. The performance levels of the power system were confirmed during these tests A maximum peak power of 14.9 MW. and a maximum average power of 14.0 MW, were obtained. While these power levels were slightly below the 15-MW. goal, these levels were achieved with plasma charges that were slightly below average in performance. Thus, any subsequent tests performed with plasma charges with average or above average performance would be expected to easily achieve the 15-MW. net output power objective. The general relationship between temperature conditioning of the plasma charges, burn rate, stagnation pressure, and output produced by the Pamir-3U system was confirmed. Because of the limited amount of test resources available, specific comparisons at identical operating points with different combustion pressures (thermal conditioning temperatures) were not performed. However, the general trend of increased power output for increased operating pressures was consistent with the results that have been obtained previously. During the acceptance test program, all elements of the Pamir-3U facility performed as expected. Except for a few minor anomalies, the entire test operation proceeded without any flaws or test delays caused by the equipment. All Pamir-3U MHD power system and facility components were undamaged during the testing and are ready for subsequent tests. All consumable items performed according to their specifications and lifetime requirements. The test program demonstrated that the Pamir-3U performed according to specification, that a test rate of three hot-fire tests per week can be achieved, and that maintenance and supporting operations can be adequately performed during the nontest periods. No damage was incurred by any of the system and subsystem components during the test program..

ADVANTAGES OF MHD SYSTEMMHD reduces overall production of hazardous fossil fuel wastes because it increases plant efficiency. In MHD coal plants, the patented commercial "Econoseed" process developed by the U.S. (see below) recycles potassium ionization seed from the fly ash captured by

the stack-gas scrubber. However, this equipment is an additional expense. If molten metal is the armature fluid of an MHD generator, care must be taken with the coolant of the electromagnetics and channel. The alkali metals commonly used as MHD fluids react violently with water. Also, the chemical byproducts of heated, electrified alkali metals and channel ceramics may be poisonous and environmentally persistent. MHD is attractive to engineers because it has no moving parts, which means that a good design might be silent, reliable, efficient and inexpensive. Also known as a caterpillar drive for submarines, this was popularized in the movie The Hunt for Red October as being a "silent drive," an undetectable stealth super weapon in submarine warfare. In reality, the current traveling through the water would create a great amount of gases, and thus noise. In the 1990s, Mitsubishi built several prototypes of ships propelled by an MHD system. These ships were only able to reach speeds of 15 km/h . A number of experimental methods of spacecraft propulsion are based on magnetohydrodynamic principles. In these the working fluid is usually a plasma or a thin cloud of ions. Some of the techniques include various kinds of ion thruster, the magnetoplasmadynamic thruster, and the variable specific impulse magnetoplasma rocket. Japan began sea trials of a prototype magnetic ship. Yamato 1 is propelled by two MHD (magnetohydrodynamic) thrusters that run without any moving parts. When completed, the MHD ship should be able to attain speeds of more than 100 knots (125 miles or 200 kilometers per hour), with little noise. This is several times the top speed of todays ships, which are slowed down by turbulence created by the ships propellers. MHD works by applying a magnetic field to an electrically conducting fluid. The electrically conducting fluid used in the MHD thruster of the Yamoto 1 is seawater. If fuel cells become common, MHD propulsors may have lower costs in some applications than electric motors driving propellers.

Diagram of yamato1

DISADVANTAGES OF MHD SYSTEMMHD generators have not been employed for large scale mass energy conversion because other techniques with comparable efficiency have a lower investment and operating cost. Advances in natural gas turbines achieved similar thermal efficiencies at lower costs, with simpler equipment than an MHD topping cycle. To get more electricity from coal, it's cheaper to simply add more low-temperature steam-generating capacity. If high efficiency is needed in a new plant, coal gasification feeding molten salt or solid oxide fuel cells is expected to have superior efficiencies because the fuel cell bypasses the inherent inefficiencies of a heat engine. However, MHD generators for fossil fuels are inherently expensive. A certain amount of electricity is required to maintain sustained magnetic field over 1 T. Because of the high temperatures, the walls of the channel must be constructed from an exceedingly heatresistant substance such as yttrium oxide or zirconium dioxide to retard oxidation. Similarly, the electrodes must be both conductive and heat-resistant at high temperatures, making tungsten a common choice. The major problem with MHD is that with current technologies it is more expensive than a propeller driven by an engine. The extra expense is from the large generator that must be driven by an engine. Such a large generator is not required when an engine directly drives a propeller.

REFERENCES www.google.com http://en.wikipedia.org www.evilmadscientist laboritries.com www.Energy Conversion and Management.com http://verdantpower.com www.encyclopedia.com