Electronic Drive Motors Used in Naval Vessels - Term Paper Example

Electric Drive Propulsion System The electric drive propulsion system being environmentally friendly are also very fuel efficient as compared to the traditionally used mechanical drive propulsion systems in the ships because of a number of reasons. The reason is very straight forward and easy to understand, a traditional mechanical drive propulsion system consists of two separate sets of turbines, one is for propulsion and the other one is for generating electricity for use for various activities on the ship whereas an electric drive propulsion system utilize only one set of turbines which serve both the purposes i.e. propulsion and generation of electricity for shipboard and other uses and run very often at the most optimum and fuel-efficient speeds. This ultimately results in increase in the Figure 1 Electric Powered Hybrid Ship [http://www.militaryaerospace.com/etc/medialib/platform-7/mae/articles/print-articles/volume-22/issue-12.Par.86459.Image.323.350.1.gif] overall efficiency of the ship and lesser consumption of fuel by the ship. According to an analysis of various ships conducted by the US Navy, the electric drive propulsion ships utilizes 10 to 25 percent lesser energy as compared to the traditional mechanical drive propulsion ships and thus are very likely to contribute to the Navy’s target of achieving environmental sustainability in consumption of fuel by its vessels and by the naval equipment (Baldwin & Baldwin, 2008). There other advantages of electric drive propulsion system because of being newer in technology it can incorporate in it the latest technology and can easily support the automated system and the various systems on the ship can be easily shifted to electric control and can easily be automated. Electric drive propulsion system can use the new propeller/stem configurations such as the podded propulsor which is very effective in increasing the fuel efficiency of the ships due the improvements in the hydrodynamic efficiency of the ships (Hobart, 1911). The incorporation of the podded propulsor system can help in further saving the fuels up to 15 percent. Figure 2 Podded Propulsor [http://accessscience.com/loadBinary.aspx?filename=YB001201FG0030.gif] While incorporating an electric drive system in a naval vessel there are other concerns beside the propulsion of the ship and the electricity required for the control room electrical panels and boards. The guns and other security equipment installed on a naval vessel are also mechanically operated and in order to convert the operation completely into an electric system the mechanical system installed on the ships will also needed to be converted to electric power. One solution is to use an integrated electric drive system with more advanced motor type known as the advanced induction motor AIM. But this type of electric motors can are only sufficient for the most primitive guns such as the DDG-1000 destroyer and cannot be used for the guns and security and combat equipments which require a larger power for their operation. The other technologies which can be used for powering the larger guns and combat equipment include permanent magnet motor (PMM) and high temperature super conducting synchronous motor (HTS). The conversion technology used should be efficient enough to convert and distribute the shipboard electrical power for the development of a propulsion system with more reliability, survivability and power quality. Permanent Magnet Motor A permanent magnet motor does not have a field winding on the stator frame and thus relies on permanent magnets to provide the magnetic field against which rotor field interacts to produce torque. The commutation under load on large motors can be easily improved by the use of compensating windings in series with the armature. The power consumption of the field winding can be easily eliminated by the use of permanent magnet fields (stators) and thus most of the large motors are dynamo types which utilize stator winding. The various operations on the ship and naval vessels powered by electrical systems require various different power ratings for the use in different types of equipments. Therefore different requirements of power ratings are fulfilled by the use of different types of motors. Permanent Magnet Motors are utilized for the equipment which requires relatively high power (Nasar, Boldea & Unnewehr, 1993). The permanent magnets cannot produce large flux and thus are very unlikely to produce the required power rating in the motor however this problem is resolved by the use of miniature permanent magnet motors that use high energy magnets made with neodymium or other strategic elements which are actually the alloys of various diamagnetic metals which include iron and boron. Miniature motors have the same structure as of the typical permanent magnet motors but they have at least three rotor poles to ensure starting regardless of rotor position. The linkage with the exteriors of the curved field magnets is formed by using steel tube housing. High Temperature Superconducting Synchronous Motors HTS or high temperature superconducting synchronous motors are electromechanical systems that utilize superconducting elements for the transmission of low voltage currents through them. Because of the low resistance offered to the superconducting elements the efficiency of the transmission and conduction of current becomes relatively high as compared to the typical conduction of current through copper wires. The use of superconducting devices also utilizes a very little space and thus reduces the size of the equipment considerably. These motors utilize direct current electromagnet field winding on the rotor and thus can provide higher power rating to the various equipments on the ship. Figure 4 High Temperature Super Conducting Synchronous Motor [http://images.machinedesign.com/images/archive/stf1newjpg_00000039111.jpg] Recently such a motor with 1600 hp has been developed and researchers are conducting researches to further increase the power rating of such motors. The most important advantage of such a motor is the smaller size and high efficiency. The high efficiency of these motors is actually due to the low resistance of the HTS windings which operate at temperatures above absolute zero (National Research Council, 1995). The composition of the field windings of such motors is highly dependent upon the purpose they have to serve and according to the output power required. Mostly the field windings of HTS are made from alloys of metals and sometimes metallic crystalline compounds as well. The most commonly used metals and compounds are bismuth, strontium calcium oxide, silver, iron and boron. The core of the motor is constructed from air core which resolves the problems related to core losses and saturation. Electric ship technologies utilize a modular, scalable and highly reliable power distribution system which incorporates a hybrid design and these electric propulsion systems are very effective and can adapt to the requirements of the ship very easily. The various salient features of the electric drive propulsion system are: 1. The fuel consumption in the ships is substantially reduced by the use of bi directional capability. 2. Same system of electric motors can be utilized for propulsion as well as for supplying electricity to the shipboard. 3. The various load requirements of the ships including the electricity load of the shipboard can be met by modular expandability. 4. The design utilized for modular expandability is user friendly and contains all the features of a hot-swappable modular design. Figure 5 Power Conversion Modules and Panels for Naval Vessels [http://atg.ga.com/EM/defense/electric_ship/images/est-1.jpg] 5. The efficiency in power distribution can be ensured by redundancy in the power distribution system. 6. The power density in electric drive propulsion ships is increased by the use of semi-conductor devices. 7. The use of semi-conductor devices ensures very less loss of energy during conversion for various operations. 8. A detailed and extensive system of power management is incorporated in the propulsion system to ensure uninterrupted supply of power for meeting the various requirements of the critical loads. 9. The electric power quality and power efficiency is greatly enhanced by the use of semi conductor devices and power management system. 10. In order to replace the mechanical equipment, mechanical motors and power systems the electrical equipment should have a capability to operate at various power ratings in order to cater the demands of the different types of on board equipments which are present on the ship. This is achieved by the use of programmable multiple output voltages which can vary the power rating of the electric motors according to the requirement of the equipment to which they are attached. 11. Motors with programmable output voltages allow them an extensive degree of automation in the control of these equipment which can substantially reduce the crew and the required on board staff and sailors. 12. The maintenance of the electrical equipment is much easier as compared to the mechanical systems because of the degree of automation achieved in the electrical designs. The electrical designs allow the use of effective maintenance techniques like fault isolation and reconfiguration. 13. The fault isolation method is very effective in maintenance of the equipment because of its ability to get isolated from the whole system. The automated electrical equipment can easily be isolated from the system because it has been programmed to get isolated when required and the operator at the central control room can isolate the faulty equipment from the whole system during maintenance. This not only allows high degree of efficiency but also is very effective way of practicing safety of the maintenance staff during the maintenance operation. Figure 6 Advanced Ship Service Distribution [http://atg.ga.com/EM/defense/electric_ship/images/est-2-sm.png] 14. The various features of the design of the electrical propulsion system are very efficient and can easily adapt to any kind of ships therefore electrical drive propulsion system can very easily be used for naval ships. The automated and electronic control system makes it very easy for the ships to incorporate newer weapon technologies and combat equipments because of the high degree of flexibility and adaptability in the power systems. 15. These ships due to their energy efficiency are environment friendly and comply with the new energy standards. 16. The high voltage electronics system are the most important and useful feature of the electrical design because it allows the efficient conversion of electricity for use on the ship. Competitors in Market Electric Drive Propulsion System incorporated in naval ships is a very innovative technology and is currently in the developmental stages and researches are being conducted to develop the technology to start production on a larger scale so that all the naval vessels and ships could be transferred to this technology. Being a new and innovative technology, the advantages are numerous and thus there are no considerable competitors in the market. The only technology which can be considered as a competitor is the traditional mechanical drive propulsion ships but the differences in the efficiency are high enough to make EDPS (Electric Drive Propulsion Ships) far better than the mechanical ones (Polmar, 2005). Figure 7 Solar Powered Ship [http://www.solarnavigator.net/images/solar_transporter_ship_orcelle.jpg] Solar powered ships also offer some competition to the technology but the issue with solar power ships is that a large amount of power required for the equipment installed on the ship cannot be derived from solar panels. The initial cost of the solar powered ships is also very high as compared to the cost of these vessels. Moreover the large solar panels required for providing a large amount of power to the vessels are very difficult to incorporate in the design of the ships and increases the size of the ship considerably (Porche, Willis & Ruszkowski, 2004). The technology has been recently tested in the US Navy and some commercial laboratories and is proven to be durable and sustainable. Funds have been allocated to research in this field and naval vessel with a 230 rpm 5 MW propulsion motor is expected to be developed by the end of 2012. Environmental Considerations The technology used in Electric Drive Propulsion System is much more efficient as compared to the traditional mechanical drive propulsion system and thus consume much less fuel making this technology environmentally friendly and sustainable. The US navy is very much concerned about the fuel consumption by its large fleets and naval vessels and wants to incorporate environment friendly technologies so as to minimize their contribution towards the carbon footprint of the world. In the current global scenario with the imminent threat of global warming the institutions and governments are planning to shift towards renewable energy sources and are also improving the energy efficiency of current non renewable fuel (fossil fuel) powered vehicles and equipment. Under such circumstances the US navy is more than willing to use such technologies which are more efficient and minimize the use of fossil fuel until the development of renewable energy powered naval vessels. So keeping in mind the environmental considerations, these naval vessels are very efficient and environment friendly and should be adopted with immediate effect. Large diesel engine powered ships and naval vessels are generally not good for environment because of their low efficiency and the ships have to run at less than the optimum speeds during various points of their journey which further reduces their efficiency thus these ships cannot be considered as environment friendly. However in electric drive propulsion, the propulsion if ship is done through electric motors and the electricity is generated through diesel powered generators on the ship. Both the technologies and systems have diesel as the same source of energy but electric drive naval vessels are considered environment friendly while the diesel drive ships are not considered as environment friendly, this is because of the following reasons: 1. The efficiency of the electric drive ships is much better as compared to the efficiency of diesel drive ships. 2. The diesel drive ships utilizes diesel powered motors for propulsion which does not operate at optimum speeds during various phases of the journey which reduces efficiency and increases the maintenance cost however the electric drive vessels utilize the electricity generated by the diesel generators on the ship. This allows the diesel generators to operate at the optimum speed and maximum efficiency all the time even if the electric motors for propulsion have to vary their speeds, thus reducing the fuel consumption and maintenance costs. 3. The electricity from the generators on the ship can be utilized for powering the motors for the operation of various guns and combat installations on the ship which are to be powered by less efficient mechanical motors in a mechanically driven ship. 4. The generators installed on these vessels comply with the emission standards provided by UNEP and US Technological, Safety and Ethical Issues The only objection which has been raised by the various economic and defense analysts on the production of these ships is the money required to be spent on the research for developing this technology and also the initial capital required for the construction of such naval vessels. Since the navy is already suffering budget deficits because of the hike in fuel prices, it does not have large funds to spend on the research and it also cannot afford to buy and construct a large number of such ships. Thus drawing a cost benefit analysis various experts have stated that the savings that will be generated by the improvement in energy efficiency and reduction in fuel consumption will be far lesser than the money that needs to be spent on the development and construction of these vehicles. The technological experts argue that there are other technologies including the solar powered ship technology which is far better in efficiency and in fact do not needs any fuel should be used as an alternative to the traditional mechanical powered ships. However they fail to provide agreeable solution to the problems related to the solar powered ships with regards to their large size and high initial capital required for their construction. Some other technological issues due to the power quality issues and harmonic distortion on the shipboard equipment include: a. Increase in the reactive losses on the electronic equipment of the control boards. b. Improper operation of the sensitive electronic equipment due to electromagnetic interference. c. Poor power quality can result in equipment breakdown as a consequence of increased insulation stresses d. Increase in the resonance phenomena and electromagnetic signature These issues can be resolved through effective power quality monitoring and using efficient conversion mechanisms. General Opinion regarding the Technology The naval research is exploring ways to power all its ships with electricity; however the opinion of the public and the experts is divided on the issue. People are generally concerned about the large sums of money being spent on the development of the technology which is far less efficient than other technologies and is not supposed to achieve the desired objective of filling the large budget deficit of the navy. According to a survey conducted on internet, most of the people actually do not want their tax money to be spent on a technology which is aimed at decreasing the budget deficit of the navy and is actually not efficient enough to do so. The awareness among the masses about the potential of solar technology is the actual reason behind this criticism because they think that utilizing solar technology which is much more energy efficient and sustainable would be a better idea than this because the pay back is much faster in that and solar powered vessels are environmentally very friendly with zero carbon emissions. Some of the people have questioned the need of development of these vessels for the navy and think that since it is the time of pulling our troops back from Afghanistan and Iraq, we should not be spending this much money on our naval vessels because most of the Americans do not want to indulge in such a long distance war in future. With the internal issues like the social security finances and the reconstruction process being carried out in flood and tornado stricken areas most of the people do not want to spend anything on the development of military at this time. The economic and defense analysts however have not criticized the idea to this extent and have acknowledged the advantages of the technology, but the cost benefit analysis drawn by most of the analysts state that the return in the form of reduction in the consumption of fuel is much lesser as compared to the initial capital required for the development of the technology. Future Prospects The future of the technology is very bright because of the interest navy is taking in the technology and is actually spending large sums of money for the development of these ships. The recent mandates from the defense department and the Congress have asked all the military and governmental institutions to cut their fuel consumption levels by increasing the energy efficiency. Certainly energy efficiency is a matter of deep concern for the government and think tanks because of two primary reasons: 1. The highly uncertain and fluctuating prices of fuels do not allow the organizations and institutions to follow their budget. 2. The deteriorating condition of the global environment and global warming has greatly increased the concerns of international community regarding the consumption of non renewable fossil fuels. The states and the organizations which do not follow the guidelines provided by the United Nations Environment Program are subjected to great criticism. Moreover under the recent mandates issued by the Congress all the governmental institutions and departments must comply with the recommendations of the Environmental Protection Agency. The high costs of fuel have recently caused problems in fulfilling the requirements of fuel by the large fleets of the navy. Under these circumstances the Navy has decided to move towards alternative approaches in powering their large fleets in order to improve efficiency and minimize the consumption of fuel. Electric propulsion systems are being considered as a very good alternative because they can provide 10 to 25 percent reductions in the fuel consumption by improving efficiency (Mikellides & Mikellides, 2011). The Navy has started the production of electric powered ships for the seven DDG 1000 Zumwalt class destroyers and the construction started in 2008 is scheduled to complete by 2012. In the first phase two ships are said to be delivered each of which will feature 78 megawatts generators for powering the electric propeller as well as the shipboard electrical equipment and electric motors to operate the guns and combat equipment. The use of electric powered ships is not new to the navy and the use of these ships dates back to 1913 when electric propellers were used in supply ships in the navy, however the current developments in the electrical and electronic technology have increased the advantages of these ships to new levels. Now the automation of the whole systems on the ships can be easily done now and the guns and the combat equipment can easily be controlled as compared to the control in case of equipment controlled by mechanically powered motors. Automation and electronic control of equipment has allowed the navy to reduce the staff and crew on the ships. Considering all these advantages, the navy is willing to finance the research that is required for the development of this technology and has also started constructing these ships. The efficient distribution of energy in these naval vessels is only due to the greater degree of control that this system offers through efficient management of energy according to the power required for the various operations on the ship. In order to achieve the set targets of reducing the fuel consumption by the naval fleets, navy will have to shift towards these ships in near future. Alternative Technologies Electric Drive Motors are being incorporated in ships and naval vessels because of the low efficiency and high fuel consumption of the diesel motors. There are other technologies which are considered as an alternative to the diesel powered naval vessels; an overview of the alternatives suggested by technological expert is as under: 1. Fuel Cell Technology: Fuel cell technology is being developed to reduce the consumption of fuel for the Navy shipboard applications. Fuel cells can provide with much more energy than generated from combustion. The proposed fuel cells can be installed on diesel powered ships, and the power from the diesel motors will only be utilized for propulsion thus reducing the fuel consumption considerably. The only disadvantage is the high initial cost of development and production (Weaver & Reidy, 2002). 2. Gas Turbines with greater Efficiency: Gas turbines with greater efficiencies can be used instead of the simple cycle gas turbines and can reduce the fuel consumption of the mechanical drive naval vessels. The disadvantage is the large size and very high initial costs. 3. Naval Nuclear Propulsion Program: Nuclear propulsion is very low in cost and construction but poses the problems of nuclear waste. 4. Sails Powered Naval Vessels: Sails powered naval vessels are also being proposed to be used by the navy for the reduction of fuel bills of navy however this type of ships cannot be used for the combat ships and can only be employed for supply ships. The disadvantage of unfavorable winds can be resolved with the help of using kite-assisted propulsion which allows better control. 5. Solar Powered Naval Vessels: Solar powered naval vessels are also being developed but there are many challenges associated with this technology as the solar powered naval vessels will be very large in size and will require batteries with very large storage capacities. Conclusion Electric Drive Motors used in naval vessels can be considered as one step forward for bringing revolution in ship technology because the major aim of the technology is to reduce the fuel consumptions and increase efficiency. The technology though environmental friendly and efficient than the previously used mechanical drive motors is not the final solution because the fuel employed is also the non renewable fossil fuel but this is a step forward towards the development of the technologies which do not require fossil fuels. References Baldwin, C., & Baldwin, R. (2008). US Navy Fighting Vessels. Paw Prints. Hobart, H. (1911). Electric Propulstion of Ships. Harper. Mikellides, I. & Mikellides, P. (2011). Electric Propulsion: theory and computation. John Wiley and Sons Nasar, S., Boldea, I., & Unnewehr, L. (1993). Permanent Magnet, Reluctance and Self Synchronous Motors. CRC Press. National Research Council. (1995). Materials for High Temperature Semi Conductor Devices. National Academies. Polmar, N. (2005). The Naval Institute guide to the ships and aircraft of the U.S. fleet. Naval Institue Press. Porche, I., Willis, H., & Ruszkowski, M. (2004). Framework for Quantifying Uncertainty in Electric Ship Design. National Defence Research Institute. Weaver G., Reidy R. (2002). World Fuel Cell: an industry profile with market with market prospects to 2010. Elsevier. Read More